Note: this page contains a large number of photos and diagrams. Current overall page download size is around 35 MB! Depending on your internet access, the page may take a while to completely download. Please be patient! I will split up the page in due time.

©2004-2022 F. Dörenberg, unless stated otherwise. All rights reserved worldwide. No part of this publication may be used without permission from the author.

Latest page updates: January 2022 (inserted section on bombing)

Previous updates: December 2021 (added ref. 230Q5, 230Q6, 230R13); 28 May 2021 (note: now about 800 literature references provided on this page, almost all downloadable!); April 2020 (started complete overhaul & expansion of this page).

red-blue line


The World War 2 Bernhard/Bernhardine radio navigation and command upload system of the  Luftwaffe is described in great detail on this website. It is a "rotating radio beam system" for fighter aircraft navigation and guidance:

Berhard station

Fig. 173: The Luftwaffe rotating beacon ground station "Bernhard" Be-10 at Hundborg/Denmark

(source: www.gyges.dk, used with permission; US gov't = no ©)

But where does this system fit within the domain of radio navigation? First, we will briefly zoom out. Radio navigation is one of the radio aids to aviation:

  • Communication (two-way):
  • ground-air, with air traffic control facilities
  • air-air, with other aircraft
  • Navigation:
  • Long-distance
  • Short-distance
  • Secondary aids (ground-operated or airborne radio Direction Finding systems, Distance Measuring Equipment)
  • Approach and landing (in particular "blind" landing, i.e., solely with reference to instruments, and with limited or absent visual contact with the runway environment, etc.)
  • Collision avoidance:
  • hazardous weather phenomena (ground-based and airborne weather radar for potential turbulence conditions; detection of low altitude windshears (incl. microbursts) on the flight path while in the airport area by ground-based and airborne doppler-radar for predictive ( = forward-looking) detection. The latter was introduced in 1994 by the Bendix company. Non-radar based reactive detection systems also exist).
  • terrain (radar/radio altimeters, ground mapping radar, and since the late 1990s: EGPWS/TAWS = GPS + 3D terrain/obstacle/airport database)
  • other aircraft (e.g., transponder-based). Of course, the opposite also exists, e.g., intercept radar used by fighter aircraft.

Also see p. 18 Trenkle Funkführungsverfahren.

"Radio Direction Finding" (D/F), Radio Location, Radio Guidance and Navigation"? This remainder of this page provides an overview of the history of the radio navigation domain, through the end of World War 2. The purpose is not to add yet another survey or taxonomy without verifiable and publicly accessible references, and rife with errors or omissions based on local-only view due to lack of foreign language skills, associated unawareness of foreign R&D, or the usual lazy copy-and-paste from other bad sources. Instead, to present an historic overview with documented origins, undistorted by persisting propagandistic or nationalistic versions of history. With extremely few exceptions, history school books reflect the "winner's" point of view, and WW2 is no exception whatsoever. I did take the liberty to place some accents based on my personal curiosity and interests, including as a pilot and user of such systems in modern times. And, like Humpty Dumpty put it so well in Lewis Caroll's "Through the looking glass": "When I use a word, it means just what I choose it to mean — neither more nor less..."


"I don't trust those high-frequency thingies. One time I flew to southern Germany and landed inadvertently in northern Germany - all because of your high-frequency thingies!"

A. Hitler

"Radio-navigation requires boxes with coils, and I hate boxes with coils!"

H. Göring

Source: ref. 5


First, we need to introduce some basic terminology regarding air navigation (which, of course, is very similar to nautical navigation). Also see ref. 185X1. Rather than describing this textually, I will let the figure below speak for itself:


Fig. 41: Some basic terminology of air navigation - very similar to nautical navigation

Directional radio-frequency (RF) waves were discovered during the late 1880s. Starting in the early 1900s, concepts, techniques, and devices were invented and developed, to apply RF to direction-finding and navigation. So, we have to introduce some more terminology:

  • Radio direction finding (RDF). As the name suggests, this is a technique for determing the direction to or from a radio transmitter. I.e., determining Angle of Arrival (AoA) or Angle of Depature (AoD), respectively. The transmitter station can be fixed-base (stationary) or mobile, and cooperative or not ( = "enemy"). The direction is measured and expressed relative to a reference direction at the D/F station or at that transmitter station. The reference direction is typically True North, local Magnetic North, or the longitudinal axis of the vehicle (ship, aircraft, land vehicle, surfaced submarine). A distinction is made between:
  • RDF (D: "Fremdpeilung"): RDF-ing of a mobile transmitter station by a receiver station with known position. If this RDF-ing is done to assist navigation of the mobile station, then 2-way radio communication between the two stations is required.
  • Reverse-RDF (D: "Eigenpeilung"): RDF-ing by a mobile receiver station of a fixed transmitter station with known position. This can be done autonomously by the mobile station.
  • Radio location, a.k.a. radio positioning: determing the position (own or of a target) by radio means. This is also known as taking a "position fix", or "fix" for short. The position can be the absolute 2D position within some coordinate system on the face of the earth, or a relative 2D position ( = D/F direction + distance/range), or the 3D position of an aircraft ( = 2D position + altitude).
  • Radio navigation, in particular in-flight. One of the mantras that I remember well from my own pilot training, is about the top priorities of every pilot/navigator: always "aviate" ( = fly the airplane), "navigate" ( = figure out where you are, where you're going, and how to get there in 4D), and "communicate" (primarily with Air Traffic Control) - in that specific order of priority! Radio navigation is pre-dated by the following other forms of navigation, even though those were/are also used by airplane navigators, in particular on trans-oceanic and trans-polar routes, out of range of radio nav stations:
  • Pilotage: visual navigation by reference to landmarks and man-made objects on the ground (or in the water). This is also known as "contact flying". So-called "steel-beam navigation" followed railway tracks (UK: railroad), also referred to as the "iron compass".
  • Celestial navigation: based assessing the angle between one or more celestial bodies (stars, sun, moon, planets) and the horizon. This method has been used by mariners since ancient times. Most of these methods require the knowledge of time (e.g, local noon). Ref. 185Y1, 185Y2. Before the establishment of dependable inertial and satellite navigation (GPS, etc.), aircraft navigators used periscopic sextants during long distance flights beyond radio range (e.g., transoceanic and polar regions).
  • A related technique is Dead Reckoning (DR). It estimates the current position, based on a previous position fix (or known position), and an estimated position-change. The latter is based on estimated speed, direction, drift and elapsed time since that previous fix. The same approach can be used to estimate position at some time in the future, based on current position (known or estimated) and conditions. An automated form of DR is the inertial navigation system (INS). Such systems use multiple linear motion and rotation sensors: accelerometers and gyrospcopes (either mechanical, ring-laser, or fiber-optic) or nanotechnology (e.g., Micro-Electro-Mechanical Systems, MEMS).

Clearly, the above radio-based activities are of strategic and tactical importance during times of armed conflict, and preparation therefore. Which also explains why corresponding RF-based countermeasures (interference, jamming, locate-and-destroy, etc.) have a similar level of importance.

Radio air navigation taxonomy

Fig. 3: Simplified taxonomy of radio-based location and navigation technology for aviation - through WW2

(note: lists of examples are not necessarily exhaustive; radar for non-navigational purposes is beyond the scope of this taxonomy)

Air navigation without radio

Fig. 3: The alternative to radio navigation....

(source: 1987, unknown)

Note that "determining" position or direction is actually "estimating", based on measurements or observations. Estimations always have an "accuracy" and a "precision". These terms are often confused, and even used interchangeably - which they are not! Simply put, "accuracy" expresses how close estimates are to the true value. "Precision" expresses how close multiple estimates of the same true value are to each other, i.e., "repeatability".

Note that with a single transmitter/DF-station pair, only a direction ( = bearing angle) can be determined - not position. The result of D/F-ing is basically a continuous straight (or great-circle) line of possible positions, emanating from the position of the D/F station, through the position of the transmitter, and beyond. This is a linear Line of Position (LoP, a.k.a., "position line"; D: "Standlinie"). See the left-hand panel of Figure 42 below.

Important: without further information, the position of the target on an LoP is not known! For a given position of the D/F or transmitter station, the LoP can be drawn on a map ("chart" in navigation parlance). Note that the bearing from a ground station to the aircraft (or vice versa) should not be confused with the aircraft's heading ( = the way the nose is pointing), nor with the aircraft's course ( = direction of the ground track, which is affected by wind).

Line of Position

Fig. 42: Linear, circular, and hyperbolic Lines of Position

Some other RF methods do not determine direction, but rather the distance ( = range) between an observer/anchor station and the "target". All points with the same distance to the anchor station now lie on a circle that is centered on that station. That is, all these points combined form a circular LoP. See Figure 42. Again, without further information, the target's position on an LoP is not known. Through air and space, radio waves propagate at the speed of light: close to 300000 km/sec, or close to 30 cm ( = 1 foot) per nanosecond. Now you know how long a nanosecond is! This finite-speed property makes it possible to use radio waves for determing distance: speed x time = distance traveled. The standard methods are as follows:

  • An fixed or mobile anchor station transmits a radio-wave pulse. That pulse is scattered from, and reflected by, the surface of the target. The target may be a cooperative/friendly, or non-cooperative/enemy aircraft, ship, land vehicle, or surfaced submarine. A reflected pulse is received back at the anchor station. The pulse has made a round-trip - to the target and back. The total time-of-flight (ToF) of the radio waves covers twice the distance between station and target. By measuring the time-difference (delay) between transmitting a pulse and receiving the echo, that distance (a.k.a. "range") is known. This is the "ranging" (D: "Enfernungsmeßung") part of what is called "Radio Detection and Ranging" (acronym: "radar") since late-WW2. The range from a radar station on ground to an airborne aircraft is actually "slant range", which is not the same as "down range". The latter is distance-over-ground, measured along the earth's surface, to the point on that surface, directly below the aircraft.
  • Rather than bouncing a radio pulse of a target, an "interrogator" station can transmit a pulse (or coded sequence thereof), and a compatible mobile "transponder" station replies with another pulse (or sequence thereof) on the same or (usually) different radio frequency. Transponders typically apply a pre-defined reply-delay. Again, half the round-trip time (minus any reply-delay) is equivalent to slant range. Modern transponders are required to apply a 3.0 ± 0.5 μsec reply delay.
  • The interrogator and transponder roles can be reversed: an airborne interrogator and a ground-based transponder. The latter is often co-located with a radio navigation beacon. The common post-war implementation of this is called Distance Measuring Equipment (DME).
  • In the world's first transponder-based ranging system (in 1927 patent nr. 632304 by Koulikoff & Chilkowsky), there were two interrogator/transponder stations. One initiated a pulse, and from thereon, the two stations ping-ponged the pulse. The resulting beat-tone was a measure of the distance between them.
  • Instead of transmitting and replying with a pulse signal, it is also possible to transmit a tone-modulated continuous wave (CW) signal, have the transponder send this back (typ. with a reply-delay) on a different frequency, and measure the phase-difference between the two signals. This round-trip difference represents a time-shift, hence distance. To avoid distance ambiguity, the wavelength of the transmitted tone has to be longer than the round-trip distance. E.g., a 10 kHz modulation tone has a wavelength of about 33 km (≈20 statute miles).

OK, just one more type of LoP to discuss! Above, we covered using the "time-difference = 2x round-trip distance" approach. It resulted in circular LoP's. This can be expanded to a system with not one but two anchor stations with known position. Of this station pair, one is referred to as the "master", the other a "slave". The master transmits an omnidirectional pulse. Upon receipt, the slave also transmits a pulse, on the same frequency. I.e., the slave is synchronized to the master. Both pulses are received by the target, where they arrive at slightly different times. Again, we have a time-difference (Time-Difference-of Arrival, TDoA). However, now this time-difference is equivalent not to a distance, but to a distance-difference! It is the difference between 1) the distance between the target and the master station, and 2) the distance between the target and the slave station. All points that have the same absolute distance difference, lie on two open curves. They are two branches of one hyperbola. The two anchor stations are the "foci" of the hyperbola. The two mirror-image curves of each hyperbola pass symmetrically between these foci. In fact, as with the linear and circular LoPs, there is an infinite family of LoP's. In this case, covering all possible distance-differences. Depending on the +/- sign of the distance difference, the target lies on one curve or on the other. So, we now have hyperbolic LoP's. See Figure 42.

In analogy with the various circular LoP methods, the same hyperbolic LoP's can also be created by pair of master-slave anchor stations that transmit a continuous-wave carier signal instead of pulses. Again, the slave is synchronized to the master. But now the LoP represents a fixed phase difference between their (continuous) transmissions, instead of a fixed time difference between pulse-pair receptions. But a phase difference between two sinewaves (audio or RF) of the same frequency is equivalent to a time difference.

As repeatedly mentioned above, without further information, the position of the target on an LoP is not known! It could be anywhere on the LoP - within the reception coverage area of the radio aids. How can this be resolved? By combining two or more independent lines of position into a point of position (PoP). For this approach to work, we need LoP's that intersect. I.e., LoPs that cross, or at least touch each other. This can be achieved with linear, circular, and hyperbolic LoP's, as illustrated in Figure 43:

Line of Position

Fig. 43A: Combining Lines of Position to estimate position

It should be intuitively obvious from this figure, that creating an accurate, clear and concise equivalent textual description is a rather tall order, and not necessarily more comprehensible or instructive. So, I will not attempt to do so. That said, a couple of words anyway...

The case of two "crossing linear LoP's" is standard classical triangulation (D: "Kreuzpeilung") - the simplest form of multi-lateration. This has been used since many centuries, if not millenia. Note that it works both ways: two (or more) fixed D/F stations can determine the position of a mobile transmitter. This was also done in the early days of radio D/F, and the position estimated by the D/F stations was reported to the transmitter station (ship, airship) via radio. Conversely, a mobile D/F station can determine its own position by using two (or more) beacon stations with known position. Accuracy ( = uncertainty) of the position estimate depends primarily on the angle between intersection LoPs. I.e., distance between the beacon pair or D/F station pair, as wel as the distance from the target to the baseline between the beacon or D/F station pair.

We can also combine a linear LoP (bearing) and a circular LoP (range). These two LoP's can be obtained with two spatially separated anchor stations: one D/F station and one range-finding station. Once can also combine a linear LoP and a circular LoP into a single system, at a single anchor station. Radar is a prime example of this. Two independent and spatially separated range-finding stations generate two overlapping circular LoP's. Conversely, a mobile interrogator station may determine the range to two spatially separated transponder stations with known position. Generally, two overlapping circles intersect at two points, not one - unless the target is located exactly on the straight baseline between the two anchor stations. I.e., there generally is ambiguity as to which of these two points is the actual position of the target. Overlapping hyperbolic LoP's can also have two intersect points.

Of course, the concept of positioning by means of intersecting LoP's also applies to hyperbolic LoP's. This is done with a chain of (at least) three anchor stations, one of which is the master to which the remaining stations of the chain are synchronized. Early such systems used maps (charts) with a lattice of hyperbolic LoP's, like the pink and light blue lines in the right-hand panel of Fig. 43 above. Each line of the lattice was marked with the associated time-difference.

Navigation is based on measurements. So we are interested in accuracy and precision of those measurements. Whereas these terms are related, they are definitely not the same! Unfortunately, they are used interchangeably by many people! Simply put: accuracy expresses how close measurements are to the true value, amount of inaccuracy is error. All measurements have some degree of uncertainty that may come from a variety of sources. whereas precision expresses how close repeated measurements of the same true value are to each other. I.e., repeatbility / reproducibility. An example of the importance of this difference is the simple "heading hold" mode of the automatic pilot of a ship or airplane. When activated, it ensures that the nose of the vehicle keeps pointing in the direction ( = heading) it had, at the moment the mode was activated. Here, the actual value of that momentary heading is completely irrelevant. As a matter of fact, the compass that provides the heading information may totally inaccurate and be as much as 180° off - no problem! A heading-hold mode will work just fine, as long as the heading information is precise, such that sign and amount of deviation from a reference heading are correct. Of course, in other cases - such as "intercept and hold a particular selected heading value", we are interested in both accuracy and precision. Unfortunately the terms error and uncertainty are often used interchangeably to describe both imprecision and inaccuracy

Likewise, when combining LoP's to make a position estimate. Note that This is inherently the case with direction finding systems that use radio beams

intersecting LoP's

Fig. 43B: The effect of Linear LoP crossing angle on the uncertainty of a trilateration position estimate

(note: distance from Station A and from B to the LoP-intersection is the same in all three cases, as is the "beam" aperture)

The situation is different when the intersecting LoP's have an accuracy that is independent of the distance from the stations - as is the case with radar and transponder type systems:

intersecting LoP's

Fig. 43C: Uncertainty areas when combining LoP's

All necessary basic methods for, and concepts of, radio D/F and radio location/positioning were patented by 1935! See the time-line diagram below:


Fig. 44: Time-line of primary radio direction-finding/location/navigation patents through 1935

(source: patent table-3)

Note: basically nothing fundamentally new has been added by subsequent radio D/F, positioning, and navigation methods, including those that are based on satellites (Global Navigation Satellite System (GNSS) uses radar to verify position of the satellites, and a "GPS" receiver performs 3D multi-lateration based on time values received from at least three satellites), WiFi networks (WPS), mobile/cellular telephone networks, etc!


Finding a direction by means of radio, implies using directive (directional) radio transmission or reception. This directivity is implemented with the antenna system at the transmitter station or at the receiving station.

An EM wave is called "vertically polarized", if the E (= electrical) field is vertically polarized. The H (magnetic) field is always perpendicular to the E field.

EM wave E & H field EM E-field dipole

Fig. XX: Linearly polarized EM wave (left) and E-field of such a wave inducing current in an aligned dipole antenna

(image source: (left) wikimedia.org CC license; (right) wikimedia.org, CC license)

Nautical authorities considered fog signalization in coastal areas and on rivers to be of prime importance. Air-acoustics warning devices, such as fog horns, sirens, whistles, guns, and bells, do no allow clear determination of direction, nor of distance. Around 1905, underwater (submarine) acoustic systems were introduced for marking obstacles and lightships, and to avoid ship-to-ship collisions during fog. Sounds were generated with underwater bells, and received with hydrophones (one on each side of the ship's hull). While at sea, this enabled reasonable determination of the direction to the signal source. In coastal areas, their use was limited to marking lightships, as the sound waves must basically be received head-on.

In Germany, fog signalling devices was the realm of the Prussian Building Authority ("preußische Bauverwaltung"), which was part of the Royal Prussian Ministry of Public Works ("Königlich-Preußisches Ministerium der öffentlichen Arbeiten"). It was very expensive to install acoustic underwater systems fixed to the sea bed. Also, the high cost of on-board equipment and their maintenance was only affordable for large ships. Therefore, in 1906, the Building Authority started to investigate directional radio signals for fog signaling, under the direction of Privy Councillor ("Geheimrat") Walter Körte. Ref. 187A1, 187A6. The Government Secretary ("Regierungsbausekretär") of the Building Authority proposed that, at times of fog, lighthouses should transmit radio signals that could be received by small ship-board receivers, with an automatically rotating parabolic antenna that would stop turning and point in the direction of the transmitter. Körte contacted the Telefunken company mid-1906, who informed him that they had already been experimenting with directional radio waves - thusfar without satisfying results.

During 1906-1908, the Prussian Building Authority performed radio direction-finding tests. These initial lab and field tests were partly done with support from the physics department of the scientific institute Urania-Berlin and equipment from the Telefunken company. Field tests took place July-August 1906 near the then-Prussian Baltic port city of Swinemünde, about 160 km northeast of Berlin (since October 1945: Świnoujście, on the Polish side of the new border). Ref. 187A5-187A7. Test signals from Swinemünde were received by a steamer at 16 nautical miles (≈30 km). The ship-board receiver used a directional parabolic antenna system (ref. 187A7). Possibly a wire antenna configured, e.g., per Fig. 2 in ref. 229E2 was used. During the 1920s, there were experiments with rotating parabolic reflectors by the Marconi company in Britain, but at VHF frequencies, ref. 228V1-228V14. Such parabolic systems were heavy, large, cumbersome, expensive, and therefore considered unsuitable for boats and small ships. To be effective, the focal length of the parabolic antenna had to be larger than a quarter wavelength! Ship-board direction-finding systems also required ship-specific calibration due to the metal hull and structures. At the same time, similar ship-board DF experiments by their French counterparts came to the same conclusions. In parallel, the Italians Artom, Bellini, and Tosi also pursued radio direction-finding (ref. 184E), but with a different antenna system arrangement. The latter approach was evaluated by the German Imperial Postal Administration ("Reichspostverwaltung"), and was deemed too large and complicated to be promising. These conclusions are not surprising for the large radio wavelengths that were practicable at the time. Also, receivers were still without electronic tube (valve) amplifiers.

Some interesting examples of RDF and R-RDF systems:

  • Komet (FuSAn 712) / Komet-Bord (FuG 124); RDF system (with acccuracy +/- 1.5° ?). Ref. 2C4, p. 123. Ref. 6G.
  • Antenna system comprised concentric rings of (vertical) antennas for multiple operational HF frequencies (short wave; 3-25 MHz); angular spacing of 3° --> 120 antennas per ring, used pair-wise (diametrically opposed) at a time [? inverse of Telefunken Kompaß - TBD], in combination with omni-directional antenna at center of the rings. Development / evaluation / experimental 1941- EOW.
  • Proved impossible/impractical to properly adjust/calibrate. Development and evaluation was done from 1941 through the end of the war (vs. abandoned per ref. 6D). Large HF ground station with an antenna array with 127 (120?) masts and 19 control huts (boxes?), with "Kometschreiber" bearing recorder/indicator in the aircraft (FuG124). Ref. 8. Experimental stage only (Bordeaux/France, Kølby/Denmark vs. Wullenweber HFDF at Kølby, ref. 230S1).
  • Ref. 20: Experimental installation with single antenna pair at Ahlimbsmühle/Germany (ca 50 km north of downtown Berlin). A complete system was also installed 1944 in the Ismaninger Moos bog area, ca. 15 km northeast of downtown Munich, but never operational. Circle diameter 2λ. Primary frequencies 5470 kHz (λ ≈ 55 m), 8345 (λ ≈ 36 m), 11455 kHz (λ ≈ 26 m).  Ref. 210F (November-1944 Luftwaffe map): Ko-1, just southwest of the village of Kølby/Denmark, planned or under construction, and the  Ko (no #) north of Munich/Germany. Ref. 210D (June-1944 Luftwaffe map): Ko-4, near Bucharest/Romania, planned or under construction. Ref. 230S1. Add map extracts? Ko-2, Ko-3? Add pano photo, SES. Combine photos into new ref. 230S2 Expand ref. 20 (pp. 64 ff)

Note that even with a single radio navigation system that only provides a Linear LoP (bearing value), the distance to/from the station can be estimated, and therewith the position! The "trick" is part of basic pilot training (well, at least it was, when I got my license). It is based on simple trigonometry: the arctangent of a right-angled triangle with a 1° angle is close to 1/60 or 1-in-60. It also requires a simple flight maneuver, time measurement, and the knowledge that there are 60 sec in a minute. The resulting rule-of-thumb is simple enough for learning by heart, and is quite helpful when "lost".

Line of Position

Fig. xxx: The simple 1-in-60 procedure for estimating distance to/from a Non-Directional Beacon (NDB)

The above distance and time estimates assume that the airplane is flying at a constant speed. Of course, the accuracy of the estimate depends not only on the accuracy of the bearing and time measurements, but also on the 1:60 approximation, and on winds aloft (as this affects speed and direction over ground). This method can be used by airborne as well as by a ground-based direction finding stations. It is referred to as the wingtip-bearing-change method, bow-to-bow bearing method, and double-the-angle-on-bow method. This method originates in marine navigation.

An interesting RDF-based navigation application is the "Zeppelin-Telefunken" multi-lateration approach-to-landing system of 1936/37. Ref. 235P9. Like airplanes, airships land with the nose turned into the wind, preferable directly upwind (to minimize lateral drift). The system in question used three landing beacons simultaneously. These three beacons (A, B, and C) were mobile: each comprised a truck-mounted 20 watt long-wave transmitter and a telescopic antenna mast. Beacons A and B were placed several kilometers upwind and downwind, respectively, of the airship mooring ( = anchor) tower at the airfield. A third beacon, C, was placed several km to the right of the mid-point between A and B. See the figure below.

Zeppelin Telefunken landing beacon system

Fig. xx: The Telefunken 3-pointer RDF instrument and the Zeppelin-Telefunken "blind" approach & landing procedure

(source: adapted from ref. 235P9)

When approaching its landing position at night or during times of reduced ground visibility, the airship would use the "A" RDF system to determine its bearing to/from beacon A and determine its position, by taking a bearing to a known navigation beacon or broadcast radio station in the area. The position estimate would then be used to navigate to a waypoint about 10 km directly downwind of the landing point between the three beacons. From there, the airship would fly upwind on the extended line between beacons A and B. The bearings to these beacons was continuously indicated by the vertical A and B pointers of a special 3-pointer instrument. See the figure above. If the A and B needles were aligned with the vertical lubber line, the airship would be on the extended A-B line. The airship would then move upwind along this line, until the deviation pointer for beacon C was horizontal. At that point, the airship was exactly above the mooring tower. It would then maintain position, typically at an altitude of about 60-100 m above ground (≈200-330 ft), lower the handling lines (ropes), descend, and then have its nose attached to the mooring tower. Ref. 41A-41D.

Clearly, for this to work, the airship had to be equipped with a triple RDF installation. There was a standard long-wave Telefunken RDF "cruise & approach" receiver" (D: "Zielflugempfänger" for 300-1800 m wavelengths (167-1000 kHz). In addition, there were two long-wave D.B.G. "bad weather landing" RDF receivers (D: "Zielfahrt"; 800-2000 m wavelengths, 150-375 kHz). All were remote controlled. D.B.G. was the Deutsche Betriebsgesellschaft für drahtlose Telegraphie m.b.H. company (also abbreviated Debeg and DEBEG). It was founded in 1911, in response to a conflict between Telefunken and Marco regarding maritime radio stations. D.B.G. primarily marketed maritime and RDF radio equipment made by Telefunken, Siemens, Lorenz (later also from Drake, Eddystone, ITT, Dancom, Sailor, and Scanti) - simply under its own brand and with its own equipment labels. Their in-house product development was very limited.

The figure below shows the control gondola (D: "Führergondel") underneath the hull of the 245 m long (800 ft) Luftschiff Zeppelin ("Zeppelin Airship") LZ 129 "Hindenburg". The RDF-room (D: "Peilraum") was in the aft part of the gondola.

Zeppelin Telefunken landing beacon system

Fig. xx: Control gondola and three RDF receivers of the LZ 129 "Hindenburg"

(source photos: adapted from ref. 41E and 187F2)

Two of the RDF antennas were installed forward of the gondola. The smaller loop, nearest the gondola, was connected to one of the D.B.G. receivers. Per ref. 41B/C it was a 2-turn loop. The larger loop was shared by the Telefunken and the second D.B.G.receiver, via transformer coupling. There was a metal ring on both sides of each loop antenna. Their purpose was to compensate for reflections and other influences by the steel frame of the airship. In addition, there two large crossing RDF wire-loop antennas on top of the hull, and at least one simple omni-directional "sense" antenna. Such antennas are used to resolve the 180° directional ambiguity that is inherent to loop antennas. There were two 3-pointer instruments: presumably one in the radio/RDF room, the other in the control room in the bow of the gondola.


Clearly, "radio" navigation per definition requires some form of "radiation". VLF to SHF microwave. Before 1887, the only human-made pollution of the electromagnetic (EM) spectrum was sparks generated with quarz flint stones to ignite fires, and tiny triboelectric effects such as observed by the Greek Thales of Miletus about 2600 years ago, when he rubbed a piece of amber - which about 2000 years later gave us the word electricity (amber = ἤλεκτρον "elektron" in Greek, "electrum" in Latin).

Rather than providing a wordy treatise on the history of radio transmitter technology, I will simply refer to the time-line diagram below and to ref. 186A-186Y.

Early transmitter technology

Fig. 45: Simplified time-line of radio transmitter technology through 1940

(source: ref. 186A-186W)

Private industry had continued to improve the spark-gap transmitter (D: "Knallfunkensender", "Knatterfunkensender"). This type of transmitter is based on using high voltage pulses to generate an electrical spark, like the spark plugs of an automobile combustion engine. The final major improvement to the spark gap transmitter was proposed by Max Wien in 1906 (ref. 186C): the so-called “tonal” or "singing" quenched-spark transmitter (D: "Löschfunkensender", "Tonfunkensender"; F: "transmetteur à étincelle musicale", ES: "transmisores de chispa sonora"). He subsequently joined the Telefunken company, where his idea was developed and commercialized. See further below. In parallel, the C. Lorenz Company (ref. 263A) had bet on Valdemar Poulsen's "spark-less" light-arc transmitter (D: "Lichtbogensender") technology. Telefunken had unsucessfully attempted to bypass Poulsen's patent during 1906-1908, then rejected the light-arc transmitter as inferior (ref. 187B).

Whereas spark gap transmitters were used on-board aircraf. For practical reasons, arc lamps and radio-frequency machine generators where not. All three technologies were doomed by the advent of vacuum tube transmitters. The demise of spark transmissions was not only caused by their inefficiency, but also by their very large occupied radio frequency bandwidth. This often caused interference, and severely limited the number of operating frequencies (so-called "tunes") that could be used simultaneously. Therefore, the International Radiotelegraph Conference of 1927 (ref. 186H) decided to immediately forbid new spark transmitter installations on land, and per 1 January 1930 in ships and aircraft (except low power). Not only installation of new stations, but also the use of undamped wave "spark" transmissions was phased out: first forbidden below 375 kHz as of 1 January 1930, then forbidden from land-based stations per 1 January 1935, and completely by 1 January of 1940 (except with less than 300 W power supply consumption, i.e., no more than about 150 watt transmitted power). §2 of article 4 of the adopted regulations also implied an immediate ban on all amateur radio use of spark transmitters. But by that time, simple vacuum tube telegraphy transmitters had already become relatively inexpensive and very efficient compared to sparkers.

The first aircraft-to-ground one-way and two-way wireless telegraphy (W/T) transmissions appear to have taken place in the USA mid-1910, with a small spark transmitter ("Morse code"). The first air-to-ground radio telephony (R/T, "voice") transmission took place about five years later, with a small 1-tube transmitter. Early aircraft had very limited propulsion power and payload. The latter is the carying capacity of the aircraft for items that are necessary to the purpose of the flight: fuel, passengers, freight, equipment, ordnance such as bombs, etc. Radio equipment comprises transmitter(s), receiver(s), associated instruments and control panels, and sometimes dedicated power supply (battery packs) or conditioner. The equipment has weight and takes up space, that is then no longer available for other payload items. Compared to ground-based radio equipment, airborne radio equipment must work reliably under significant vibration levels, temperature and pressure variations - difficult for early vacuum tube technology. High-power radios may imply larger and heavier power generators. Vacuum tube technology did make it possible to build radio-frequency amplifiers. This also greatly improved receiver sensitivity, and, hence, significantly increased the range of radio communication and navigation. Finally, antennas typically protrude from the fuselage or wings and cause drag - which reduces fuel range and maximum speed.


Directional radio beacons can be thought of as the radio equivalent of optical rotating beacons: nautical lighthouses.

In October of 1906, USA patent nr. 833034 was awarded to Lee de Forest for his "Aerophare" (misspelled "aerophore" in the patent). It proposes some form of directional antenna (e.g., parabolic reflector, or a slanted mono-pole antenna per ref. 186Q1) that is slowly rotated, and a spark gap transmitter. Note that the parabolic/cylindrical reflector was not new: it was invented by Heinrich Hertz during his late 1880s experiments, used in 1900 by Jonathan Zenneck (ref. 186G), by Lee de Forest in 1901, and in 1902 by Karl Ferdinand Braun. The latter also invented the Cathode Ray Tube (CRT, Braun's Tube, D: "Braun'sche Röhre") and the oscilloscope in 1897, the capacitor-inductor oscillator circuit in 1901, and a rotable directive transmitter in 1905. It is unclear to what extent de Forest's beacon was ever built and tested.

The motor also powers a generator and rotates a "signalling wheel" disk, in sync with the antenna. The disk has notches and a contact that interrupts the generator voltage, before it is up-transformed and passed to the spark gap. The notches implement a distinct pattern of "Morse code" dots & dashes for each of azimuth/compass sectors, e.g., 16. So, de Forest's contribution is limited to the code disk and application to radio location / navigation.


Fig. 46: Lee de Forest's December 1905 "Aerophare" concept of a rotating directional beacon with sector identification transmission

(source: adapted from US patent 833034)

In 1909, the Prussian Building Authority considered the quenched-spark transmitter to be sufficiently mature, and abandoned mobile radio direction-finding receivers. Instead, it decided to pursue a directional radio beacon on land, and a relatively simple standard receiver on-board. Mid-1909, it was proposed to build two transmitter stations on Müggelsee Lake (about 20 km southeast of the city center of Berlin), ref.187A5:

  • A Bellini-Tosi system on the site of the Royal Inland Fisheries Institute (D: "Königliches Institut für Binnenfischerei") at Friedrichshagen. This comprised two orthogonal antenna pairs, and an Artom radio-goniometer to rotate the directivity of the antenna system. It possibly was as large as 36 m tall (≈120 ft), and 127 m wide (≈415 ft) at the base (p. 351 in ref. 186L).
  • A directional transmitting station to the east of there, on higher terrain outside the nearby village of Rahnsdorf. The antenna system was to comprise 32 masts that supported 16 dipole antennas in a star configuration. The dipoles were to be aligned with standard compass directions. The dipoles were to be energized in sequence, to obtain a (stepwise) electro-mechanically rotating radio beam - the world's first rotating radio navigation beacon! Per ref. 2A, the switching mechanism was motorized. A separate Morse-code-like sequence of "dots" and "dashes" was to be transmitted by each dipole. Most likely, this was exactly the same scheme as used during follow-on tests around 1912 at Cape Arkona (see further below). The receiver station determined the direction from which the transmitted signals arrived ( = Angle of Arrival, AoA), based on identifying the dipole from which the smallest signal was received.


Fig. 46: Map of Müggelsee (ca. 4.3x2.6 km / 2.7x1.6 miles) with Friedrichshagen and Rahnsdorf

(source: "Pharus-Plan Berlin-Oberspree 1919" tourist map)

During 1912-1913, the offices and labs of the Maritime Navigation Markers Test Site (D: "Seezeichenversuchsfeld") of the Maritime Navigation Markers Office (D: "Seezeichenausschuss") of the Ministry of Public Works were built next to the Fisheries Institute (ref. 187A2-187A3, also right-hand image in Fig. 46 above), and their facilities moved there from Berlin-Tiergarten.

The mention of a Bellini-Tosi (B-T) system for transmitting is somewhat unusual. Such systems (two crossing loop antennas with radio goniometer coupling) were primarily used as DF receiving stations, not transmitter stations. Also, a 3-mast B-T would have been non-standard. Per ref. 187A7, only one small 16-dipole transmitting station was built on Müggelsee Lake. Per ref. 187C1-187C3 (Telefunken, 1912), there were actually two transmitter stations, one of which had a rather large 16-dipole antenna system: a diameter of 200 m (≈660 ft). Telegraphy engineer Franz Kiebitz (at that time working at the Imperial Postal Administration) participated in the receiving tests from a boat on the lake.

Per ref. 187A5, two medium-wave frequencies were proposed to be used: around 2.4 and 3 MHz (wavelength of 125 and 100 m, respectively). This coulds explain the simultaneous proposal for two transmitter stations. These frequencies were roughly the demonstrated practical upper limit of spark transmitters at the time. However, these two frequencies are actually too close together to warrant two separate installations, or even two test series. Per ref. 187A7, the actual antenna system was small. However, per ref. 187C1-187C3 (Telefunken, 1912), the actual circular antenna installation had a diameter of about 200 m (≈660 ft). That would have been more appropriate for a standard ½ wavelength wire dipole, resonant on an operating frequency around 300/(2x200) ≈ 0.715 MHz = 715 kHz. Undoubtedly, small standard commercial quenched spark gap transmitters from Telefunken were used. They had an operating frequency of ca. 500-1000 kHz. However, there is no law of physics that states or implies that an antenna will not radiate efficiently, unless it is dimensioned so as to be resonant at the operating frequency. Shorter dipoles could have been used (with loss of directivity), with appropriate impedance adaptation between the transmitter output and the antenna (which causes loss of power). Then again, the stated qualification "small" is relative, and no reference is provided, such as the electrical wavelength or the physical size of a human. Note that either way, even a diameter of 200 m was small compared to the wavelength of several km (!) of early transmitter systems.

You may wonder "16 does not divide nicely into the 360° of a compass. So, why 16 dipoles and not 18?" Astronomers already divided the circle into 360 degrees in antiquity. However, the magnetic compass came into use only about 1000 years ago. Initially, sailors referred to eight principal wind directions: north, northeast, east, etc. I.e., the four cardinal directions and the four intercardinal (= ordinal) directions. As nautical compasses improved, the compass rose ("scale") was further divided into eight "half winds", to form the 16-wind compass rose. A further split added 16 "quarter winds", for a total of 32 "compass points" (D: "nautische Strich", "Kompassstrich"). Each point of the 32-wind rose represents a compass sector of 360°/32=11¼°.

The Minister of Public Works explicitly stated in a letter of November of 1909, that the Prussian Building Authority went public with their system concept, in order to make it "unpatentable" (ref. 187A1, 187A5). Per § 1 and §2 of the German patent law of 1891 (applicable in 1909): "Patents are only awarded for new inventions that have a commercial application" and "An invention is not considered new, if at the time of filing, the invention has already been published within the last 100 years, or has evidently been used within the country such that an other expert could use it." Therefore, the publication indeed effectively blocked such a patent.

The transmitter antenna system comprised dipole antennas, because 1) they have a clear directional radiation pattern, and 2) their construction is very simple.

NOTE that in some old literature and patents, the term "dipole" is used for each "dipole half" (a.k.a. "leg") and each "half" is considered and counted as a separate antenna. Likewise, the words "transmitter" ("Sender") and "receiver" ("Empfänger") are often used for the transmitting or receiving antenna, not for the device that energizes the antenna with radio-frequency signals or converts radio signals captured by the antenna to audio signals. Also be aware that through the 1940s, there are cases where "Ultra High Frequency" (UHF) is used as the frequency-equivalent of the "ultra short wave" (D: "Ultrakurzwelle", UKW) band. The prefix "ultra" simply means "beyond" in Latin. In modern times, the frequency band above HF (3-30 MHz) is actually the "Very High Frequency" (VHF) band of 30-300 MHz, whereas UHF is 300 MHz - 3 GHz. 

The next figure shows the doughnut (torus) shaped radiation pattern of a dipole antenna:

Dipole pattern

Fig. 47: Radiation pattern of a dipole in "free space"

Dipole pattern

Figure 48: 2D dipole pattern

The cross-section of the doughnut has a "figure-of-8" shape. This is very directional, with a sharp null direction along the two radiating elements. I.e., through the center of the doughnut hole. Note that the "null" minimum is much sharper than the flat maximum. Hence, the "null" is preferred for direction-finding.

However, this 3D pattern is only valid in so-called "free space". That is, very far away from ground, from reflective objects, and from objects that can electrically couple with it. Typically not stated in textbooks, is that doughnut represents "total gain" of the antenna. This is the combination of "vertical gain" (i.e., the relative strength of the radiated vertically polarized field) and "horizontal gain". These gains have quite different patterns! The closer a dipole is to ground (or an equivalent horizontal reflecting ground plane), the more of its radiated energy will be reflected upward. The antenna becomes a "cloud warmer" when used for transmission! With decreasing installation height, the 3D total-gain pattern becomes oblong, shorter and taller. That is: less directive. For low angles (i.e., closer to the ground), the "total gain" radiation pattern becomes peanut shaped - still directive, but not as much as in free-space. The "vertical gain" and "horizontal gain" patterns remain quite directional. See Figure 48 below.

Some older literature (e.g., ref. 187C1-187C3 (Telefunken, 1912), 187E1-E2) only appears to consider "vertical gain", which has its maximum in the extended in-line direction of the dipole wires. However, the "horizontal gain" and "total gain have their (larger) maximum broadside to these wires, and a "null" in-line with the wires. This may explain some mixed test results at that time, with horizontal and vertical antennas on the receiver side...

Dipole pattern

Fig. 49: Radiation pattern of a dipole close(r) to ground

Clearly, the radiation pattern is symmetrical. It has a "null" or minimum direction in two opposite directions. Likewise, it has a maximum in two opposite directions. These bi-directional min and max directions are at right angles (90°, orthogonal). These symmetries pose a problem for direction-finding methods that are based on detection of the min or max direction. There are always two such opposite directions. I.e., there is always a 180° ambiguity! Note that this direction-finding ambiguity problem is exactly the same when using a rotating or rotable symmetrical pattern on the transmitter side, or on the receiver side. Such direction-finding systems provide a Linear Line of Position, as discussed in the previous section. The ambiguity can only be resolved by additional information: triangulation with another station, or being able to exclude one of the two LoP directions by other methods (e.g., one LoP direction is over land, whereas the receiver is at sea).

Due to delays and "adverse cirumstances", the Building Authority performed no further tests during 1909-1910. However, the tests at Müggelsee Lake had been successful enough to warrant construction in 1911 of a new antenna system, this time at the Fog Signal Test Station (“Funknebelsignalversuchsstation”) at Cape Arkona. Arkona (misspelled Arcona in some literature) is located 250 km due north of the center of Berlin, on the tip of the Baltic isle of Rügen - Germany´s largest island. This site was chosen to test under realistic operational conditions, and also such that in case of successful completion of the tests program, the system could be used to secure shipping traffic of the state rail ferry between Sassnitz (Saßnitz) on Rügen, and Trelleborg on the southern tip of Sweden (≈100 km).

Contrary to the installation at Friedrichshagen, this time it was a large antenna system. It comprised 32 short masts (2.6 m, ≈8.5 ft), evely spaced on a circle with a diameter of 115 m (≈377 ft), with a tall mast (2.6+43.8=46.4 m, ≈152 ft) at the center. Sixteen dipoles were strung from the central mast. Ref. 187C1-187C3. The dipoles were arranged radially, in a star configuration, i.e., one for every 11¼ degrees. The center of this star, the feedpoint of the dipoles, was raised more than the tips of the dipoles. Such dipoles are also called "inverted-V" dipoles. The span of the dipoles was about equal to the diameter of the circle. For standard half-wavelength dipoles, this implies a medium-wave operating frequency of about 300/(2x115) = 1.3 MHz = 1300 kHz. Due to the size of the installation, it was decided to involve the Telefunken company. To reduce cost and expedite construction, Telefunken recommended an antenna configuration that was different from the one used at Müggelsee Lake. The Müggelsee configuration turned out to be more suitable. So, the Building Authority decided to continue without Telefunken. Maybe this is why the 1912 Telefunken publications on this topic (ref. 187C1-187C3) mention Friedrichshagen but not Arkona!


Fig. 50: 1911 site plan for the Fog Signal test site at Arkona, with encoding of 16 dipole signals

(source: adapted from de.wikipedia.org, retrieved 15 April 2020)

During the summer of 1912, the Building Authority conducted a second series of tests, this time with an antenna arrangement "similar to that used at Müggelsee Lake, with minor modifications". Construction of this station was completed by October of 1912. It was a small system: eight 20 m tall wooden masts (≈66 ft), evenly spaced around a circle with a diameter of 40 m (≈130 ft), and a transmitter equipment shed near the center. See the photo below. There appears to be a support mast with a ball on top, just to the left of the shed. It is only about half as tall as the other masts, and is not at the center of the circle.


Fig. 51: The eight wooden antenna masts and small equipment shed at the Arkona test site - 1912

(source: 187K)

These antennas were installed within the earthen walls of the 12th century slavic Jarosmargburg hillfort. Remnants of the eight tripod masts and the associated tie down stakes were recorded in an archeologic site survey of 1921:


Fig. 52A: A 1921 archeological survey of the medieval Jarosmarburg site on Cape Arkona

(source: adapted from de.wikipedia.org; original 1921 survey drawn by Robert Koldewey; tripod masts marked blue, stakes marked red)


Fig. 52B: The tip of Cape Arkona in modern times - approximate location of the antenna ring is marked with a yellow circle

(source original unedited photo: unknown)

A much larger antenna circle would not have fit within these earthen walls. The 1921 survey also did not record remnants of a larger circle of masts. So the large antenna system must have been installed somewhere else on the Cape, outside the walls. Note that the entire terrain inside these walls slopes upward towards the cliffs on the eastern side, with a rather steep 6% grade ( ≈3 m rise across the 40 m circle).

Tests were conducted through the end of 1912, using ship-board receivers on a passenger steamer and on one of the rail ferries. These were basically still simple, passive crystal sets ("Detektorempfänger"). Direction finding was possible out to 32 nautical miles (≈60 km), and signals could be distinginguished all the way to Trelleborg (≈100 km). Due to lack of funding, tests could not be repeated under various sorts of bad weather conditions and day/night variations in radio propagation. Possible improvements were considered in 1913 and planned to be implemented and tested at Arkona in 1914, with equipment of the Building Authority, Telefunken, and of the company “Dr. Huth-Berlin”. However, World War I interfered with this plan. War can indeed be quite a nuisance and a kill-joy...

Per ref. 187A7, tests with this small system showed that an accuracy of half a compass point (i.e., ≈6°) was feasible, based on averaging. But doesn't eight masts imply only four dipole antennas?! So, how was this demonstrated directivity obtained? Well, even in Germany, there was no law that dipoles had to be straight! Four dipoles in a star configuration gives you eight dipole halves, evenly spaced by 360°/8=45°. These halves can also be connected as horizontal-V dipoles (bent dipoles), instead of straight dipoles. This way, the "null beam" can be steered in twice as many fixed paired directions, thereby doubling the achievable bearing accuracy without changing the numebr of dipoles. See the figure below (c.f. the 3-dipole example on p. 421 in ref. 186A). The aformentioned Franz Kiebitz actually conceived the required "half angle" antenna switching arrangment:


Fig. 53: Sixteen "null" (or "maximum") directions obtainable with 8 dipoles

(the four possible straight dipoles are marked in green; source antenna switching arrangement: Fig. 1067 in ref. 187R)

Down to a V-angle of 45°, the general shape of the far-field dipole radiation pattern is not very sensitive to that angle. It is also not very sensitive to the sag of the dipole wires towards their feed-point at the center of the circle. But even so, there would still only be 16 paired "null/minimum" (or "maximum") directions spread out over 360°... Note that with 16 dipoles, the same technique would result in 16x2=32 paired "null" directions. Of course, this would have made the antenna switching system significantly more complicated! But that's not all! The system concept requires that the receiver station identify the dipole with the strongest or weakest signal in the direction of the receiver. For this to work, all dipoles must generate the same field strength. This was basically done by ensuring that all dipoles had close to the same antenna current when connected to the transmitter ("it is antenna current that radiates"). For identical dipoles and a homogeneous environment, this is relatively straightforward. This only required a single adjustment of the coupled coils at the output of the transmitter. However, when the dipole configuration is changed from "straight" to "shallow V" or "sharp V", the feed point impedance of the dipole changes significantly. This would then have required switcheable adjustment of the coupling coils, or switching between at least two sets of such coils. This was definitely a disadvantage with respect to simply doubling the number of dipoles. Note that the available literature does not mention how fast any of the above systems rotated. Of course, for proof-of-concept testing and application to navigation of ships, this was not of prime importance.

As mentioned above, the Prussian Building Authority first contacted the Telefunken company in 1906, at which time the company was already investigating directional radio transmissions - without much success. The Authority first engaged Telefunken in 1911 for the activities at Arkona. In 1907, Austrian-born Alexander Meißner (also spelled Meissner) joined Telefunken in Berlin, where he worked on radio direction-finding, radio location, directional radio transmission, and associated antenna technology. Ref. 187G, 187L. Meißner (also) pioneered transmitters using radio tubes/valves, and conceived a vacuum-tube feedback oscillator around the same time (1911-1913) as did F. Lowenstein, L. de Forest, E. Reisz, C.S. Franklin, H.J. Round, E.H. Armstrong, I. Langmuir, O. Nussbaumer, S. Strauss, A. Sinding-Larsen, and others. Due to near-insuppressible worldwide nationalism (at least regarding inventions), rather lax patent criteria notably in the USA, general ignorance regarding "invention" vs. "patent", and limited understanding of foreign languages, typically only one of these names is recognized and credited in any individual country.

But anyway, in 1911, Meißner developed what became known as the "Telefunken Kompass Sender". Ref. 184AE, 187C-187H. This literally translates to "compass transmitting station". Note that this is the opposite of the term "radio compass" in the English language, which is a radio direction finding receiving installation. As is clear from his 1912 US patent 1135604, Meißner's system makes several important practical improvements to the rotating dipole-beam system of the Prussian Building Authority:

  • Sequentially transmitting an identical signal (e.g., a short pulse) via the dipoles, instead of a dipole-specific pulse-sequence or tone.
  • Using a timing signal to announce the start of the rotation sequence. This could be a single pulse or a station identifcation code, distinct from the signal transmitted via the dipoles. Of course, this signal now had to be transmitted in a non-directional/omni-directional manner, as it had to be received throughout the entire coverage area of the beacon. A natural choice would be to start the dipole sequence with the dipole that has its null in the north-south direction. The the timing signal would then be equivalent to a North-signal.
  • Patent text page 1 (numbered lines 94-96) proposes to create the required non-directional pattern by simultaneously connecting all dipoles in parallel. From a switching point of view, this not as easy as it sounds. Possibly, this was the configuration tried by Telefunken at Arkona and deemed problematic by the Building Authority... However, the patent also proposes a separate omni-directional "umbrella" antenna (lines 99-101 on text page 1, lines 16, 19, 20 on page 2, and in patent figure 2 shown in Fig. 54 below). Consistent with this, the commutator/distributor in the patent figure connects to the dipoles as well as to an omni-antenna. The latter is accommodated just like an additional dipole would have been, by simply adding two contacts to the commutator.
  • Note that the same transmitter is used for the non-directional transmission as for the directional transmissions. During non-directional transmssion, the radio energy is spread out evenly in all 360° directions, instead of being concentrated in the figure-of-8 beam of single dipole. Hence, the received omni-signal is always weaker than the strongest dipole signal.
  • As shown in patent figure 2, the omni and dipole antennas would share a central mast. The dipole legs are no longer straight: each leg is bent into an inverted-V, and the dipole feed point is near ground level. This is not to be confused with an inverted-V dipole: it has straight legs, and the feed point is higher than the tips of the dipole.
  • The dipoles switching part of the Building Authority system was motorized. A rotary contact arrangement would have been the logical choice. That system also had secondary motorized switching mechanism for creating the dipole-specific "dot" and "dash" pulse sequences. In the patent diagram, this is implemented as an interupter disk in series with the signal from the transmitter. Unfortunately, there are no details available of the Building Authority system that allow us to determine if, or to what extent, Meißner's commutator was different.
  • Significantly simplifying the telegraphist's job at the receiver station. It was no longer needed to interpret the various dot/dash dipole signals. Instead, he simply had to measure the time between the north/time-signal and passage of the weakest dipole signal. The patent proposes a special stopwatch for this purpose. Its needle rotates at the same speed as the antenna commutator.

Interestingly, Meißner's patent was filed in August of 1912, after Telefunken 1912 publications such as ref. 187C1-187C3, and after Telefunken demonstrated a working scale model at the April 1912 Allgemeine Luftfahrzeug-Ausstellung (ALA) aviation exhibition in Berlin, ref. 187M! The patent obviously lists Meissner as inventor. For some reason, it does not list any assignee, even though he was working at Telefunken. There is no equivalent German patent, and elsewhere, there only appears to be one in The Netherlands (octrooi nr. 981, filed July 1912). The same switched multi-dipole star-configuration, but now for radio direction finding receiving purposes, appears in the 1919 German patent 423014 about inductive leader-cable systems for ship navigation.

Telefunken Kompass-Sender

Fig. 54: Cross-section of the antenna system, the transmitter/commutator, and the Telefunken stopwatch

(source: diagram adapted from Meißner's 1912 US patent 1135604; also Fig. 3 in ref. 187C1-C3; stopwatch adapted from Fig. 2 in ref. 187D)

The face of the Telefunken stopwatch shows a circle with 34 tick marks, see Fig. 54. The ticks at the 12 and 6 o'clock position are marked "z" for "Zeit", i.e., reception of the time signal, ref. 186G4. There is one tick mark pair for each dipole antenna. I.e., 32 ticks in total. They are counted from 0 to 31, where "North" = 0 and "South" = 16. The ticks for the cardinal and intercardinal points of the compass are marked with the standard corresponding German letters N, O, S, W, and NO, SO, SW, NW, respectively. Note that the stopwatch does not have a conventional hand (needle), but a double one - across the entire watch face. It represents the two null-directions of a dipole antenna, and the associated 180° ambiguity.

According to ref. 187C1-187C3, the Telefunken Compass transmitted the north/timing signal after each half revolution of the commutator. This makes perfect sense. During a full commutator revolution, each of the 16 dipoles is energized twice, and the receiver station observes two null-passages. If the north/time signal were only sent once, then the second of these null passages would normally be wasted, and double the time between measurements. Note that with a single north-time-signal, using the second null instead of the first, does not change the measured bearing angle, with its 180° ambiguity. The antenna commutator turned at 2 rpm, i.e., one full revolution every 30 sec (though ref. 187F2 states 1 rpm). Hence, half a revolution took 15 sec.

The principle of the Telefunken Compass system is illustrated in the animation below. In this animation, the audio pulse tone is 1000 Hz, the standard for Telefunken quenched spark transmitters, see further below. The tone is not sinusoidal, but a "spark" spike with a decaying tail (see top left-hand corner of Fig. 45 above). This replicates the rough sound of a quenched spark tone. I have included some background static noise, for added realism.

One cycle of the "Telefunken Kompass Sender" system (note: in reality, the time scale & stopwatch needle would move smoothly)

(move mouse/cursor over image to show player controls)

Reports that the system achieved an accuracy of about 3-4° (e.g., ref. 187C1-187C3, 1912), may refer to accuracy of reading the angle on the stopwatch (ref. 2A) or after averaging multiple "null" passages. The average human reaction time to aural stimuli is about 0.25 sec, which would correspond to 6°/sec x 0.25 sec ≈ 1.5°. A significantly improvement the system accuracy would have required an impractical number of dipoles (ref. 184L, 1921).

A prototype of Meißner's Kompaßstation was built and tested at a Telefunken test site in Berlin-Gartenfeld (spelled Gartenfelde in old Telefunken publications). This is an 800 m (≈½ mi) wide triangular area, surrounded by canals. It is located between Berlin-Spandau and what had been the canon and rifle shooting ranges of the Imperial Artillery ("kaiserliche Artillerie") and home of the 1st Prussian Airship Battalion ("1. preußische Luftschiffer-Batalion") at Reinickendorf. The ranges were closed after near-misses with boats on the adjacent lake and a granade hitting a residential house in 1908. The former shooting range and airship area became Berlin-Tegel airport in 1948. Gartenfeld was acquired by the Siemens company late 1910 and was appended to Siemensstadt ("Siemens Town"), adjacent to the south. The Siemens Gartenfeld Cable Works ("Kabelwerk Gartenfeld", part of the Pirelli company since 1998) closed in 2002.

Telefunken Kompass-Sender

Fig. 55: Section of a 1912 map of greater Berlin; the blue triangle marks Gartenfeld island

(source: adapted from wikipedia.org)

Per ref. 187C1-187C3, the central mast of the prototype antenna system was about 20 m tall. This is consistent with the roof ridge of the equipment shed in the photo below being about 2.5 m above ground.


Fig. 56: The Telefunken Compass test site at Gartenfeld near Berlin-Spandau

(source: ref. 187C2)

The figure below shows three photos of Meißner's antenna commutator system. The photo at the center was taken inside the equipment shed in Fig. 56 above. The photo on the right was taken at Telefunken's equipment exhibition at the June 1912 International Radiotelegraph Conference in London (ref. 187D). It was decided at this same conference to relegate transmissions of telegraphy signals used exclusively for direction-finding and location of ships to wavelengths up to 150 m (i.e., frequencies above 2 MHz).

Let's first look at the left-hand photo. It corresponds to Meissner's 1912 US patent 1135604. At the top is a ring with porcelain insulators: one pair for each of the 16 connected dipole antennas and one omni-antenna), each with a ball-shaped contact at the bottom. It appears that these balls could "swing" to and from the central support. The antenna feed-line wires were connected just above the ball contacts. Below this ring are the two rotating arms of the commutator. There is a porcelain insulators at the end of each arm, again with a ball-shaped contact, now pointing upward. Just below the rotating arms are two slip rings that rotate with the arms. Each of the associated sliding contacts is mounted on a vertical rod, with a porcelain insulator at the base. Just above these insulators, the rods are connected to a quenched spark transmitter.

Telefunken Kompass-Sender

Fig. 57: The "Meißner" motorized transmitter distributor / antenna commutator

(source: (left) ref. 187C2 (also in 187C1 & C3); (center) ref. 187C2; (right) ref. 187D)

Also note the vertical disk between the motor and one of these two insulators. The motor is down-geared, and drives the disk and the rotating arms in synchrony. The disk has a series of cams/notches that actuate a normally-closed switch contact. One of the two connections to the transmitter is passed through this contact. This allowed a short Morse-code station identification to be transmitted instead of the start/North pulse signal, while the commutator was connected to an omni-directional antenna. Note that there is no such disk near the commutator-motor in the center and right-hand photos. In the center photo, it appears to be mounted on a small shelf against the outside wall, below a set of eight porcelain insulator disks. This disk has its own motor, so it was not synchronized to the commutator.

In the center and right-hand photo above, the transmitter is mounted directly below the base plate of the commutator. See the next figure. It is a Telefunken model "0,5 T.K." quenched-spark gap transmitter. As the model designator suggests, it had an output power of 0.5 kW. It dissipated over 1 kW. There is a large spiral inductor on the front side of the transmitter. It is made of copper tape. Behind this coil, there are three "Leyden jar" capacitors, connected in parallel. Combined, the inductor and capacitors determine the operating frequency of the transmitter. The frequency was adjustable by selecting taps on the front of the coil. Standard frequency range of the "0,5 TK" was ca. 500-1000 kHz, equivalent to a "medium wave" wavelength of 300-600 m. This could be customized down to 330 kHz (900 m, longwave). Next to the antenna-current meter, there is a frame in which a stack of porcelain insulators and copper electrode disks (with 0.2-0.3 mm mica insulating spacer rings) is compressed. This is a 10-section series spark gap "Funkenlöschstrecke": the actual quenched spark gap device! The copper disks were partially silver plated. They had a large diameter, to increase cooling and thereby improve "quenching" of the sparks. In the center and right-hand photos above, three additional copper-tape coils are visible below the transmitter. They are part of an adjustable antenna tuning circuit.

Telefunken Kompass-Sender

Fig. 58: Telefunken quenched-spark transmitter model "0,5 T.K." used in the early model "Kompass Sender"

(source: (left) ref. 187C; color photos adapted from ref. 186D)

The transmitter was powered by an AC motor-generator. It converted standard 220 V / 50 Hz AC power to 220 V / 500 Hz. A step-up transformer increased the latter to the required high voltage: ca. 8000 volt. The number of spark gaps depended on the desired transmitter power, e.g., 60 gaps for 35 kW. The rpm of the motor-generator was adjustable. This allowed ±30% variation of the nominal tone of the transmitted amplitude-modulated radio signal: 500 Hz AC power generated a 1000 Hz tone, as the transmitter "fires" each half-wave of the AC power (i.e., twice per 500 Hz cycle).

The Telefunken "0,5 TK" sales brochure mentions a range of 100-150 km over land (200 km at night), and 200-300 km over open sea (400 km at night), when using 20-30 m tall T-antennas at both the transmitter and receiver. The 1.5 kW model "1,5 TK" also operated on 500-1000 kHz and had an advertised range of 700 km. Ref. 186D, 186J1.

In 1912, a complete chain of 33 of such beacons was proposed, spaced 50 - 100 km along the entire "political border" of Germany (ref. 187C1-187C3, 187H):

Telefunken Kompass-Sender

Fig. 59: Map of the Telefunken Compass beacon chain along the border of the German Reich, as proposed in 1912

(source: ref. 187H)

The beacon stations were to have used Telefunken ½ kW transmitters, powered by the local electricity grid, and be fully automated: no need for operating staff/personnel.

In 1914, the US Navy began to evaluate radio direction finding systems on Fire Island, a narrow barrier island along the south side of Long Island, New York. The Navy Bureau of Equipment purchased a Bellini-Tosi directional receiver system and a Telefunken Compass transmitter system. Construction drawings of the foundations of the "Telefunken Aerial" and the "Telefunken Compass Building" are dated July 1914 - June 1915 (ref. 187P). Actual testing probably took place in 1916 (ref. 187E1). Per ref. 187N, the central mast was about 30 m tall (100 ft) and the dipole antennas spaced 20°. This spacing implies eight dipoles, so the spacing was actually two compass points, i.e., 2 x 11¼° = 22½°. As shown in Fig. 53 above, it would have been possible to transmit with one compass point spacing. That same reference states that the commutator shorted out all dipoles, except the one being used to transmit. It also states that a different code letter was transmitted via each dipole. I.e., Telefunken had "borrowed" the scheme from the original system of the Prussian Building Authority and Lee de Forest's patent! Demonstrated bearing accuracy was about 5 - 10°, which was deemed acceptable for rough navigation of commercial vessels, but not for war-time military vessels.

In the end, only two "Telefunken Compass" stations were built in Germany. They were constructed early 1917 and were operational through the end of WW-1 (November 1918). One station was built at the village of Bedburg-Hau, on the southeast side of Cleve in Germany, just south of where the river Rhine crosses into The Netherlands. These days, the "Funkturmstraße" (lit. "Radio Tower Street") in Hau is a reminder of exactly where the station was located. Cleve is spelled Kleve since a German spelling reform of July 1935, and is spelled Cleves in English. In 1939, a large "Knickebein" fixed-beam station was built in Materborn, on the west side of Cleve. The second Compass station was built at Tondern, ca. 43 km northwest of Flensburg. This area was Danish territory before 1864 and after World War 1, with the village name spelled Tønder. There was an airship base of the German Imperial Navy ("kaiserliche Marine") on the north side of the village. The two stations were used by German ships, submarines, and for long-range navigation of dirigibles built by the Zeppelin, Parseval, Schütte-Lanz, and Basenach companies (ref. 1, 2, 185G, 185H, 235L). When airship losses became unsustainable (they were an easy prey), they were phased out and replaced by "Groß-Flugzeuge" ("G-Flugzeuge" = "large aircraft" bombers) and "Riesen-Flugzeuge" ("R-Flugzeuge" = "Giant aircraft" longe range bombers, with wings spans of 28-55 m ≈ 90-180 ft). These also used the Compasses. The German military referred to these beacons generically as "Richtungssendeanlage" (RSA), i.e., directionally transmitting station.

Over southwestern England, the Line of Position of the two Compass stations crossed at a sharp angle. Not surprisingly, it was found that this made the position estimates less accurate. This is illustrated in the Figure 43B above.

Obviously, the beacons were deactivated at the end of WW-1. The station at Cleve was dismantled in 1926, on orders of the Belgian occupational forces in that area (ref. 187J). Note: upon German default on WW-I reparation payments, French and Belgian troops invaded the German Rhineland area from January of 1923 until July of 1930. This  basically the German area west of the Rhine river, i.e., all the way up to just north of Cleve, and a strip along the east bank. The industrial Ruhr area was occupied until August of 1925.

According to ref. 187R, the main wooden antenna mast stood 75 m tall (≈245 ft). Per ref. 187J, the trellis mast was made of American pitch pine, a dense high-strength hard wood. Thirty (!) dipoles were suspended from the top of the main mast, down to sixty support masts (standard "Telegraphenstangen", i.e., telegraph/telephone poles) that were spaced evenly on a circle with a diameter of 2x125=250 m (≈820 ft). Note: ref. 187R mentions both 125 and 130 m as diameter. The support masts were 12 m (≈40 ft) tall. There were five evenly spaced "crow's nest" platforms on the main mast, see Fig. 60 below. The dipole wires were strung from each support mast to an insulator on the outside the upper platform, i.e., several meters below the top of the mast. Hence the top of the antennas was ca.70 m above ground level. From there, the wires went all the way straight down and were attached to an insulator at each platform. This implies that there was no separate omni-directional antenna, and that omni-directional transmission was done via all dipoles simultaneously, as confirmed by the schematic in Fig. 61 below.

Telefunken Kompass-Sender

Fig. 60: The wooden central mast of the Telefunken "Kompass Sender" near Cleve (left) and Tondern (center)

(source: ref. 187J (left), Fig. 1090 and Fig. 1085 in ref. 187R)

Compared to older implementations, the number of dipole antennas was increased from 16 to 30. This improved direction-finding accuracy to ca. 2°. Per ref. 187R, there was no Meißner-commutator between the transmitter and the dipoles. Instead, there was a very large toroidal coil ("Trommelspule", "Ringspule") with a diameter of 2 m (6.6 ft)! This coil comprised 720 wire-turns with 60 evenly spaced taps for the 30 dipole antennas. Inside the coil, similar to the Meißner-commutator, an arm rotated. There was a sliding brush at both ends of the arm. It connected via slip rings to a 4 kW Telefunken quenched spark transmitter (possibly a model "4 TV", ref. 186J1). Compared to the standard radio goniometer, this toroidal coil had a more homogeneous coil field, and rotation did not cause undesirable capacitance variation (ref. 184B), and associated frequency variation.

Telefunken Kompass-Sender

Fig. 61: The transmission control system of the Telefunken Kompass stations at Kleve and Tönder

(source: adapted from Fig. 1091 in ref. 187R)

A large number of cam disks was used to transmit the various Morse-code identifier and timing signals, and to switch between the directional and the omni-directional antenna configuration. At the center of the diagram above, there is a cam disk marked "Flimmerzeichen" , i.e., "blinker". Its purpose is to transmit rapid short pulses instead of a constant signal, to improve accurate detection by the receiver station of the signal null/minimum.

The shafts of the cam disks were driven by a system made by the company Carl Zeiss (renowned for its lenses and scientific instruments) in the city of Jena, about 225 km southwest of Berlin. The drive system was regulated by an accurate clock (±0.2 sec/day), made by the Riefler precision-clock company in Munich. For omni-directional transmission, all dipole wires were connected together by bridging the two sliding brushes, while one side of the transmitter was connected to ground/earth.

Per ref. 187R, the Telefunken Kompass stations at Cleve and Tondern used the following transmision sequence, see Fig. 62:

  • First, the station at Cleve ("Station C") repeatedly transmitted its identifier ("Stationszeichen"), the Morse-code letters "CCC", 3x "─ • ─ •", during 42 sec. This was an omni-directional transmission.
  • This was followed by the "start" sequence ("Loszeichen"): the Morse-code punctuation character "=" (dash-dot-dot-dot-dash, "─ • • • ─"), followed by the letters "O" (dash-dash-dash, "─ ─ ─") and "S" (dot-dot-dot, "• • •"). The last "dot" of this sequence was the actual start signal. This sequence was also transmitted omni-directionally.
  • Then a constant tone signal ("Peilungsstrich") was transmitted with rotating directivity for 80 sec, at two rpm. So, receiving stations would observe a signal null/minimum every 15 sec.
  • Finally, a termination signal ("Schlußzeichen") was sent, again omni-directionally: the Morse-code procedure sign (prosign) AR (for the Morse procedure word "new page", dot-dash-dot-dash-dot, "• ─ • ─ •"), followed by the punctuation character ":" (dash-dash-dash-dot-dot-dot , "─ ─ ─ • • •"). The final "dot" coincided with "north" passage of the null-direction, exactly 90 sec after the last "dot" of the "start" sequence.
  • Ten second laters, the station at Tondern ("Station B") would start its 90 sec sequence, but used the Morse-code letters "BBB" (3x "─ • • • ") as station identifier.
  • Both stations transmitted on the same radio frequency, around 165 kHz (1800 m, long-wave).

Telefunken Kompass-Sender

Fig. 62: Relative timing of the Cleve and Tönder Telefunken Kompass stations

(source: Fig. 1088 in ref. 187R)

During 1918, civilian radio listeners in The Netherlands (a neutral country during WW1) became aware of regular transmissions by "mysterious" directional radio stations in Germany, with cyclically varying signal strength. Their observations, conjectures, and conclusions were discussed in several issues of the monthly magazine of The Netherlands' Telegraphy Association, ref. 187Q1-187Q9. These private observations were supplemented with measurements by several direction-finding and listening stations of the Royal Netherlands Navy, Army, and several schools. For example, for the "c" station, the following was observed:

  • Transmission sequences started at 4 minutes past the full and half hour.
  • Each sequence started with omni-directional transmission that consisted of:
  • five groups of three letters "C" (5x3x "─ • ─ •"),
  • then the Morse-code prosign AS (used for both "wait" and for ampersand, i.e., the character "&", "• ─ • • •"),
  • and finally the group "EEE", i.e., three "dots" ("•"). The last "dot" would have signified the "start stopwatch" signal.
  • On other occasions, the "C" station sent its sequences every 15 minutes:
  • the C-series,
  • followed by the "double dash" punctuation character "=" (dash-dot-dot-dot-dash, "─ • • • ─ ")
  • and finally the punctuation character ":". The latter character is "dash-dash-dash-dot-dot-dot" ("─ ─ ─ • • •). Again, the last "dot" signified the "start stopwatch" signal.
  • Some observations only mention gradually increasing and decreasing signal strength, i.e., not stepwise. Others reported that the directional transmission sequence comprised long dashes of about three seconds each (ref. 187Q1).
  • Note that for an antenna system with 16 dipoles, this implies one revolution in 60 seconds, with a 0.75 sec pause between dashes. I.e., as if there was a commutator switches between consecutive dipoles.
  • Some observations mention passage of 5 or 6 minimums during a 90 sec cycle. I.e., 15 sec between minimums. This is consistent with the 2 rpm rotational speed.
  • Based on the received sound, it had to be a "fluitvonkstation", literally a "whistling spark station", i.e., a quenched spark transmitter.

By triangulation, listeners determined that the "C" station was the Telefunken Radio Compass at Cleve, and "B" the station at Tondern. All participating receiving stations were within 100-200 km (≈ 60-125 mi) from beacon "C". Signals received from that beacon never disappeared completely during the minimums. I.e., the minimums of the radiation pattern were not true "nulls". The receivers were 175-500 km (≈ 110-310 mi) from beacon "B". During the long (wide) minimum, no signal was received. Only one listener ever claimed to have heard an "é" ("dot-dot-dash-dot-dot", "• • ─ • •") station.

The 1919 Reichs Patent nr. 328279 of Leo Pungs and Hans Harbich (both of Telefunken's competitor C. Lorenz AG) proposes to replace the toroidal coil with an arrangement of two concentric cylindrical coils, the outer one being a stationary non-contact drum armature ("Trommelspule") with a special coil winding scheme, the inner one rotating and coupled to the transmitter (see Fig. 1083 in ref. 187R). Mr. Pungs (author of ref. 187R) also patented a special stop-clock for use with a Radio Compass (RP 328274, May 1917), to accurately measure the time between two successive null/minimum signal passages, instead of between the North/Start-signal and the first null/minium passage.

Of course, the original Telefunken "Kompass Uhr" stopwatch could still be used, with its nautical "compass points" scale (see Fig. 54). However, a special high-resolution direction-finding stop-clock "Peiluhr" was developed, see Fig. 62 below. Its single-hand made a step every 0.1 sec, making its rotation seem continuous. This, combined with the high number of dipoles (30 vs. 16) and the goniometer instead of a commutator, the obtainable accuracy was improved to about 1° (ref. 187R).

Telefunken Kompass-Sender

Fig. 63: "Peiluhr" direction-finding clock for use with the Telefunken Kompass

(source: Fig. 1089 in ref. 187R)

As Meissner mentions in his 1928 German patent 529891, the accuracy that could be obtained with the Telefunken Compass system depended on the stopwatch operator and the relatively low rotational speed of the beacon. This required averaging of several consecutive bearing measurements, a rather time-consuming process that was only acceptable for slowly moving boats and ships. His patent proposes to replace the stopwatch with an optical indicator that "somehow" rotates synchronously with the beam of a beacon that rotates at very high speed (e.g., 20 rps = 1200 rpm!). The pulses received from sweep-by of the rotating beam would be converted to two almost-stationary light spots (spaced 180°) at the corresponding positions on a compass scale.

This was basically the end of the line for this first generation of rotating-beam radio navigation beacons - until the latter half of the 1920s...


During first decades of the 20th century, there was a lot of experimentation going on in the field of directional antenna systems (ref. 185M), the use of directional radio reception and transmission, in particular for maritime navigation. Most of it contributed to knowledge and experience, but did not lead to long lived applications. As shown above, the latest version of the Telefunken Compass was the first operational continuously rotating beam beacon. An interesting British example of a large rotating beam system is the one constructed in 1920 on the small isle of Inchkeith in the Firth of Forth, some 10 km northeast of downtown Edinburg/Scotland. Ref. 228V6. It was a cooperation of the Marconi company (designed and developed by Charles Samuel Franklin) and Trinity House, in its role as General Lighthouse Authority (which, by the way, had no authority in the Scottish part of Great Britain). It was based on Marconi's late 1890s and 1916 experiments in Italy with rotable parabolic cylindrical reflectors and 2-3 m wavelength (100-150 MHz), ref. 228V14. Heinrich Hertz was the very first to use this type of radio reflectors (1888, ref. 228V16). The Marconi beacon had two such reflectors, installed back-to-back, and with an aperture of 8 m. However, instead of a solid metal surface, these reflectors were "curtain" screens, each made up of about two dozen parallel vertical wires, spaced about 30 cm (1 ft). Also see the 1919 US Marconi/Franklin "reflectors" US patent nr. 1301473. A solid surface would have been much too heavy, expensive, and with a very high wind load. A spark transmitter with a wavelength of 4 m (75 MHz) was used. This initial beacon at Inchkeith was operated for about a year, and tested with the steamship "S.S. Pharos" during the fall of 1920. A vertical monopole transmitter antenna was placed on the axis of symmetry of each parabola, typically about ¼ wavelength in front of it. This configuration generated two sharp radio beams in opposite directions, sweeping at a constant speed of ½ rpm (one revolution in 2 minutes = one beam passage per minute!), very much like an optical lighthouse. The spark transmitter operated on a wavelength around 4 m (ref. 228V2), i.e., a frequency around 70 MHz (VHF). Ship-board, only a simple receiver installation was required (ref. 228V8). However, due to the beacon's operating frequency, it had to be a special short-wave receiver, which was not standard equipment... Ref. 228A. Around 1921/1922, the initial beacon was replaced with a larger one. The antenna system was about 10 m tall (32 ft per ref. 228V5), with arms of similar length (ref. 185F, p. 34). During the spring of 1922, it was tested with the "S.S. Royal Scot" of the London & Edinburgh Steamship Co. Beam patterns were determined at wavelengths of 4.28 m, 5.54 m, and 6.14 m, i.e., at 70, 54, and 49 MHz.

Inchkeith beacon

Fig. 64: The  antenna of the Marconi Rotating Beam system - under construction on Inchkeith

(source: (left image) Fig. 5 in ref. 228V6 & Fig. 12 in ref. 228V14, (right image) ref. 228V1; see Fig. 106 in ref. 228V7 for a different view)

Inchkeith beacon

Fig. 65: Receiving antennas for the Marconi Rotating Beam system on the "S.S. Royal Scot"

(source: adapted from ref. 228V1)

To enable the receiving station to determine its bearing from the beacon, these beacons sent a distinct Morse signal at each of 64 half-compass-points, i.e, every 5.625°. See see Fig. 65B below. I.e., the same approach as pioneered by Lee de Forest's 1905 concept and the 1909 stepwise rotating beam system of the Prussian Building Authority. The 360° dots-and-dashes sequence of the Marconi beacon was transmitted at an equivalent leasurely Morse Code Speed of about four words per minute (4 WPM ≈ 200 dots, dashes, and inter- & intra-character spacing). So no trained Morse code operator was required to use the system. A bearing accuracy of a quarter compass point was obtained (≈2.8°). Ref. 228V2, 228V3.

Marconi beacon morse codes

Fig. 65B: The Morse Code letter designations of the 64 half-compass-points

(source: adapted from Fig. 11 in ref. 228V14)

Ca. 1923, Marconi erected a second revolving double-reflector beacon: next to the South Foreland Light Station (lighthouse), just to the northeast of Dover/England, right above the famous white cliffs. Ref. 228V11. However, it had a flat reflector instead of parabolic. See Figure 66 below. Like the Inchkeith beacon, it rotated at 0.5 rpm. It operated on a wavelength of 6 m (50 MHz), and had a range of 50-100 miles. Around 1928, Marconi abandoned his rotating beam developments, in favor of his commercial radio communication activities.

Marconi South Foreland beacon

Fig. 66: South Foreland lighthouse with Marconi revolving beam beacon to the right - ca. 1930

(source: photo adapted from St. Margaret's Village History, inset adapted from ref. 228V11)

In 1916, the British government established the Department of Scientific and Industrial Research (DSIR). The Department formed the Radio Research Board (RRB) in January of 1920. In 1925, (Sub-)Committee "C" (Directional Wireless) of the Board initiated preliminary tests of a radio beacon system with a loop antenna that rotated through 360°. Loop antennas have radiation pattern similar to dipole antennas, i.e., a figure-of-eight shape, with two null/minimum directions that are spaced by 180°, and two flat maximum directions. See Fig. 48 above and Fig. 67B below. Using rotating loops for direction-finding reception was common practice, and based on reciprocity, the same directional pattern applies to transmission. This was not a novelty at that time (ref. 228A). These tests were performed by the Royal Aircraft Establishment (RAE) based at Farnborough airfield, located about 50 km (≈33 miles) southwest of downtown London. The test installation was set up at Gosport's WW1 RAF airfield (at nearby Ft. Monckton per ref. 228B, 228D, 228S2), located on the Channel coast near Portsmouth, about 60 km southwest of Farnborough. The beacon was erected 1925 (ref. 228Y, 1926 per ref. 228Z). It operated on a wavelength of 707 m (424 kHz) and the loop antenna was a 5x5 ft (≈1.5x1.5 m) square, with six turns of wire (ref. 228R). To reduce the wire's loss resistance (important, as the antenna was extremely small compared to the wavelength), the wire comprised 1458 insulated strands of SWG 40 wire ( = 0.1118 mm diam). Ref. 228R, 228S1. Experiments showed that for open-sea ranges up to 50-60 miles, all observed bearings agreed to within 5° of bearing estimated with other methods (themselves with 1-2° accuracy), and about 70% of all cases agreed within 2°. During subsequent experiments with ships anchored at 90-100 miles, the bearings agreed within 4°. At distances beyond 60 miles, noticeable night-effects were observed, as with other DF methods. These effects were more serious beyond 90 miles. Ref. 228C, 228D.

Early 1928, it was concluded that these experiments were promising enough to warrant full-scale trials with a more permanent beacon. The decision to proceed was taken shortly thereafter. The costs and the work were to be shared by the Air Ministry and Trinity House. Ref. 228K. In November of 1928, the cost was estimated at GB£5k, ref. 228J. Based simply on the inflation rate data for general goods and services, this would be equivalent to about £316 thousand in 2019 (≈€360k, ≈US$428k). The site selected for these trials was the Orford Ness, for its coastline location and for financial reasons. As the name suggests, Orford Ness is a headland, or "ness". There are no records of monstrous nessy beings ever having been sighted here - at least not of the aquatic kind and not more than in the local human population. This narrow peninsula is some 15 km (≈9 miles) long, and is separated from the Suffolk/England mainland by the Alde-Ore estuary. The widest part of the ness is off the village of Orford, about 130 km (≈80 miles) northeast of downtown London. The ness was acquired by the British War Department in 1913/14. The ness became the site of the first Royal Flying Corps (RFC) air research station in 1913. The associated military airfield became operational in 1915. The ness remained a restricted military site through 1982, including WW2 radar development, atomic and conventional weapons research, and over-the-horizon radar trials.

Formal purpose of the trials with the Orfordness (one word!) Beacon was to test practical utility for various classes of ships and for aviation, investigate transmitter power requirements vs. operating frequency for a certain desired operating range, investigate limitations regarding siting, and estimate operating and maintenance cost for full-scale operation. However, per communications from the Air Ministry to the Treasury, the Ministry's actual motivation was the importance to RAF aerial navigation, in particular at night, and for direction-finding with standard on-board radio equipment. Ref. 228F2, 228K. Construction of the building for supporting the rotating-loop antenna and for housing the associated radio equipment, started in January of 1929. The beacon building is located 475 m west of the 1792 Orford Lighthouse, also located on the ness. The beacon officially entered into service on 20 June 1929, after some initial test flights by the RAF.

Orfordness Beacon

Fig. 67A: The Orfordness Beacon with barracks to the left and electrical "power house" to the right

(source: adapted from Orford_Ness_23, © 2008 Simon James, Creative Commons Attribution-Share Alike 2.0 Generic license)

The ground level of the beacon building is an octagonal concrete box with an external buttress at each corner. This concrete base is close to 3 m heigh (≈10 ft), ref. 228Q. Applying this dimension as a reference to available photos, the pointed roof of the beacon building is about 5 m across and the tip of the roof at about 10.5 m (≈35 ft) above ground. The upper structure housed the transmitter and motor drive for the antenna. It is timber framed and covered with tarred wooden clapboard (weatherboard) siding. This is why the National Trust (who acquired the Ness from the UK Ministry of Defence in 1993) named it the "black beacon". Entry to the upper levels is via external stairs. The delapidated beacon building was restored in 1994. The original timber central drive shaft of the loop antenna is still inside the building. The beacon was powered via cables by large (30 kW) WW1-vintage generators at the airfield site on the ness. The brick powerhouse in the photo above (about 6x8 m in size) housed a much smaller generator. It was built early 1933, to reduce operating costs and also to serve a new bombing range that was under construction at the time.

The loop antenna was a small multi-turn "frame coil" loop of about 3x3 m square (10x10 ft, ref. 228M3). The loop was vertically oriented and mounted on a vertical wooden shaft that poked through the roof of the beacon. No other technical details are available regarding this antenna. It rotated with a speed of 1 rpm, i.e., 6° per sec. To ensure accuracy of the system, this speed had to be constant and precise. A "phonic motor" was used to achieve this (ref. 228K). Its concept was invented by Poul la Cour in Denmark in 1885 and patented by him in Britain in 1887. Ref. 228P. It was originally used to synchronize telegraphy and teleprinter systems, as well as J.L. Baird's television system. In essence, it uses a stable electric oscillator to drive a synchronous motor. Since the 1920s, this was implented with a simple electronic audio tone generator. Its signal drives an electromagnet that is coupled to a mechanical tuning fork and continuously excites the fork. Tuning forks can only oscillate at a specific audible frequency (hence "phonic"). The resulting precise, constant fork vibration is captured via capacitive coupling. This signal is then amplified to the required power level for the synchronous AC motor. The fork's frequency was based on the rpm set-point and the number of poles per phase of the AC motor. Deriving an audio frequency from a highly stable and precise source, like a high frequency quarz crystal oscillator, was neither practicable, nor were such oscillators and the necessary frequency dividers available at the time. Per ref. 228L, this drive system maintained the beacon's 1 rpm to within 0.01 sec per rev. (note: this implies a rather amazing 0.02%!). "North" was aligned with True North, not Magnetic North (ref. 228N). In modern aviation, beacons such as VOR (VHF Omi-directional Range) are referenced to Magnetic North, not True North, as local Magnetic North is the only reference direction that can still be determined when all of the aircraft's electrical and vacuum systems have failed. I.e., when only the magnetic "whisk(e)y" compass remains.

Orfordness Beacon

Fig. 67B: The Orfordness Beacon - with what the antenna might have looked like, and the loop radiation pattern

(source: adapted from Orford_Ness_23, © 2008 Simon James, Creative Commons Attribution-Share Alike 2.0 Generic license)

The beacon transmitted on a a wavelength of about 1040 m, i.e., a long-wave frequency of 288.5 kHz (ref. 228Y). There are no clear references regarding the output power of the transmitter, of which only a small fraction was actually radiated, given the very small size of the loop compared to the wavelength. When operational (ref. 228H1-228H11), the beacon repeated a fixed transmission sequence, starting at the full hour. During the first minute of each sequence, the station call sign (GFP) was repeatedly sent in slow Morse code. Then a continuous tone-modulated carrier signal was sent for five minutes. This was followed by five minutes of silence. Ref. 228H1-228H11, 228K, 228N.

In April of 1930, it was decided to build a second such beacon, at the Royal Aircraft Establishment (RAE) site at Cove near Farnborough/Hampshire (ref. 228H4, 228K). The RAE had a Radio & Navigation Department at Cove. The stated objective was "to test the general utility of this system of direction finding and to ascertain in particular, whether by obtaining bearings from the two beacons [ = triangulation], aircraft can fix their position with sufficient accuracy for practical purposes". The beacon became operational in November of 1930. The Cove/Farnborough beacon transmitted during the five-minute intervals during which the Orfordness beacon was silent.

Orfordness Beacon

Fig. 68: Particulars of the two primary beacons and beacon locations

(source: based on ref. 228H4)

An omni-directional "North" signal was transmitted while the "nulls" of the antenna radiation pattern swept through the North and South direction. This signal was a single Morse-code character (see Fig. 68). As soon as the constant tone started after this Morse character, the receiving station started the stopwatch (ref. 228N). The stopwatch was stopped upon subsequent passage of the beam's "null". This is referred to as an "ingenious technique" in ref. 262F (p. 4, pdf p. 18; 1948). But it is exactly the same method as patented by Meißner in 1912 and implemented with the Telefunken "Compass". See the section above. In the Telefunken Compass, the rotation was stopped during transmission of the North signal, and that signal was transmitted via a separate, omni-directional antenna. Here, only a directional antenna is used, and it rotates non-stop. So, if the receiver was located close to due north or south of the beacon, the North signal could not be received. Therefore, the beacon also transmitted an "East" signal that could be used instead of the "North" signal. Of course, 90° had to be added to the bearing measurement). The "East" signal was not (and could not) be used to resolve the 180° ambiguity that is caused by the antenna radiation pattern having two diametrically opposed null-directions.

A "sufficiently accurate" stopwatch or other chronograph had to be used. Such a stopwatch could have a special dial "somewhat similar in type to that proposed for use with the Telefunken Compass in 1912" (ref. 228L), see Fig. 69 below. Instead of a stopwatch, a sort of strip-chart or other ondulator recorder could also be used to measure the time between "North" or "East" signal and subsequent "null" passage. The recorder could be automated. Ref. 228M, 235P45.

Orfordness Beacon stopwatch

Fig. 69: Stopwatch dials for use with the rotating beacon

(source: adapted from ref. 228L)

All civil pilots and merchant marine radio operators were invited to use the beacons and report accuracy to the Air Ministry (ref. 228H4). During the initial nine months of operation (ref. 228D), the general conclusion from reports submitted by ships was that accurate bearings were obtainable with "ordinary" receivers at a range of 50-100 miles (presumably nautical miles), and up to 250 miles with "more elaborate" receivers. During the subsequent nine months (ref. 228E, 228F2), about 160 ships submitted reception reports. Participating ships, anchored within 45 miles, recorded an accuracy no worse than 1° compared to true bearings accurately determined by other DF means(themselves typically with 1-2° accuracy). Overall, with "normal modern" receivers (i.e., 1- or 2-tubes/valves), a reliable range on the order of 100 miles was obtained, day and night, with an accuracy no worse than 2° in about 80% of the cases. With slightly degraded-but-workable accuracy, a range of 250 miles was obtained, and up to 500 miles with more sensitive receivers. A few ships reported accurate bearings at ranges from 400 - 900 miles. Ref. 228F2. The German Küstenfunkstelle (coastal radio station) at Cuxhaven and at Norddeich, located at ca. 425 and 525 km northeast of Orford, also provided signal reports. Ref. 228K. As to be expected for a land-based long- or medium-wave beacon, ships also observed a 1-2° shoreline effect (a.k.a. "coastal deviation", "coast refraction") around certain directions. I.e., beam bending towards the shore line. Ref. 228F2, 228N. The RAF performed tests with three bombers in May of 1931, but results were inconclusive. Ref. 228K.

In October of 1934, it was decided to shut down both the Orford and Cove/Tangmere beacon (ref. 228K). From a military point of view, such beacons were considered to have a fatal flaw: they could be hijacked by enemy transmitters. The British revisited this perceived vulnerability when they attemped to bend and "spoof" the German WW2 "Knickebein" beam in 1939/1940. However, it appears that the 1934 decision was rescinded at some point: per Air Ministry Notice to Airmen No. 32 of 1938 (ref. 228H11), the Orfordness beacon was (still or again) active in 1938. Per ref. 228N (1939), the beacons at Orford and Tangmere (though with the Farnborough call sign GFT) were still active in August of 1939. Also, in 1939, there was an experimental rotating loop beacon at the mouth of the China Bakir River in Myanmar (frmr. Burma, under British rule until January of 1948), about 50 km south of Rangoon. It transmitted on 285.7 kHz with the callsign XZP. Other than the call sign and the North signal, "the remaining signals are as for Orfordness Beacon" (ref. 228N). This beacon was built by the Marconi Company in 1932 (ref. 228U).

At the beginning of WW2, the only radio navigation aids at the disposal of the RAF were medium frequency (MF) and high frequency (HF) radio direction finding ground stations, and the Lorenz Standard Beam Approach (SBA) "bad weather" landing-beacon system (ref. 230V, 1945)...


Otto Scheller obtained well over 70 patents, primarily while working at the C. Lorenz company in Berlin. Two of his patents have been absolutely fundamental and groundbreaking. They have found widespread application in aircraft radio navigation, from the late 1920s to the present time (!) - both en route and for approach and landing.

Lorenz-Scheller A/N system

Fig. 70: The 1907 and 1916 Scheller patents for course-line radio beacons

Scheller's first patent, German Imperial Patent nr. 201496, dates back to 1907. Keep in mind, both “radio” and "aviation" were still in their early infancy! At the time, he had just left the London-based Amalgamated Radio-Telegraph Co. Ltd. (Poulsen/De Forest, 1906-1908) to join the C. Lorenz AG company in Berlin. He initially continued to work on Poulsen light-arc transmitters. Lorenz competed with Telefunken on transmitters, and acquired Poulsen patents in 1907. The Scheller patent in question lists neither Lorenz, nor Amalgamated as patent owner/assignee... This patent proposes the following (ref. 229C1):

  • Using directional radio means to create a sharply defined line in space. This line is easy to locate, even under poor weather conditions, incl. reduced visibility. This could be used by mobile receiving stations as a position marker or course line for marking shipping lanes.
  • Note: in those days, aviation did not yet need the means to navigate other than by simple visual reference to landmarks and man-made objects (a.k.a., "pilotage").
  • Such course lines to be generated by two co-located antenna systems, each with a "figure-of-8" directional radiation pattern and operating on the same radio frequency.
  • Scheller proposes two pairs of vertical antennas, see Figure 60 below. The paired vertical arrangement is covered by Scheller's patent nr. 192524, also from 1907. It uses a single transmitter source of "undamped" (continuous) waves, inductively coupled to both vertical radiators of the pair.
  • This 2-pair antenna configuration was "borrowed" over a decade later by Frank Adcock, as part of his 1919 Direction Finding patent (GB 130,490). Adcock also proposed a configuration with elevated vertical dipoles (not practical for LF/MF/HF frequencies) instead of monopoles, and added compensation/elimination of common-mode signals by adding 180° phase shift between the two antennas of each pair, resulting in a "2 crossing H's" configuration. Likewise, around 1933, the U.S. National Bureau of Standards abandoned pairs of loop antennas (also with a "figure-of-8" directional radiation pattern) in favor of the Scheller arrangement of two pairs of vertical antennas. See further below.
  • The two antenna systems to be angled with respect to each other, such that the lobes of their radiation patterns partially overlap, and a narrow common line of same-strength signals is created. This is referred to as the equi-signal beam / zone / course line.
  • As the patent drawing above illustrates, this creates not one, but four equi-signal course lines that emanate from the beacon. One pair of these can be narrower than the other.
  • The two antenna systems to be energized in a distinct alternating on/off manner. E.g., one transmits “dots” ("•", the letter "E" in Morse code), the other “dashes” ("─", the letter "T"), such that one is always transmitting. I.e., it is an "interlocked" system: there are no pauses between successive
  • "E/T" is the simplest combination of distinct interlocking pulses: "E" = "dot ", "•", "T" = "dash", "─". The most widely used complementary Morse code letter combination was A/N ("A" = "dot dash", "• ─", "N" = "dash dot", "─ •").
  • Other combinations that were used are F/L ("F" = "dot dot dash dot", "• • ─ •", "L" = "dot dash dot dot", "• ─ • •"); D/U ("D" = "dash dot dot", "─ • •", "U" = "dot dot dash", "• • ─"), K/I ("K" = "dash dot dash", "─ • ─, "I" = "dot dot", "• •"); X/S ("X" = dash dot dot dash", "─ • • ─", "S" = "dot dot dot", "• • •"); O/I ("O" = "dash dash dash", "─ ─ ─", "I" = "dot dot", "• •"); A/I ("A" = "dot dash", "• ─", "I" = "dot dot", "• •"). Ref. 229D, 229R18, 235X4, 254.
  • Note: Scheller's patent does not consider sending two different tones instead of two distinct on/off signals - “wireless telephony” transmission with variable tone modulation was still in the very early experimental stage at that time.
  • On the equi-signal line, a mobile receiver station will hear a constant sound. When moving away from the equi-signal line, one of the two audio signals will become predominant. This allows detection of course deviation as such, as well as determination of the direction of this deviation (i.e., to the "E" side or to the "T" side of the equi-signal line).
  • The direction of the four equi-signal course lines can be changed with respect to each other, by modifying the relative transmission power of the two antenna systems.
  • This is expanded by Scheller’s 1916 patent (nr. 299753), in which he proposes to use a radio-goniometer to rotate the entire transmitted 4-course radiation pattern. I.e., without the need to physically rotate the entire antenna system, or move the relative positions of the transmitting antennas. This 1916 patent also mentions the use of a radio-goniometer to make the equi-signal beams wider or narrower.
  • Multiple, sharply defined equi-signal lines can be created by changing the relative transmission power of the two antenna systems in a cyclic manner.
  • This was later done in the 12-Course Radio Range system in the US, and German World War II multi-beam beacon systems such as “Erika”, “Sonne”, etc.
  • If only a single course line is desired, two uni-directional antenna systems should be used, instead of bi-directional ones.
  • This concept was later used in all VHF/UHF Instrument Landing Systems (ILS).
  • Use a stationary radio receiver station located on the equi-signal line, for monitoring the transmissions.
  • Constant monitoring rapidly became standard practice for all radio navigation beacons.

Note: German patents had a "term of protection" (validity period) of 15 years. In 1920, the validity of patents that expired during WW1 was extended internationally by up to the duration of WW1. The normal validity period of German patents was increased to 20 years in 1988. This period is counted from the day following the patent application (a.k.a. filing date), not from the patent award or publication date - which may be months or even years after the application. However, exclusive right of use and the right to prevent others from using the invention do become effective with publication of the patent grant. Of course, a patent only provides legal protection in the country where it was awarded.

The following plots show the horizontal radiation pattern of two pairs of vertical antennas, placed at the corners of a square, as in Scheller's patent. The polar plot on the left corresponds to the lines A11-A2 and B1-B2 crossing at right angles (90°) in the figure above. The plot on the right is for crossing at 45°/135°: two of the overlapping zones are now much narrower, two are much wider.

Lorenz-Scheller A/N system

Fig. 71: Horizontal radiation pattern of the Scheller antenna configuration - for 90°/90° and 45°/135° crossing angles

(the two pairs of associated NEC files of my 4NEC2 antenna simulation model are here, here, here, and here)

The next figure shows the 3D radiation patterns for the same two pairs of vertical antennas, for the 90° crossing-angle case:

Lorenz-Scheller A/N system

Fig. 72: 3D radiation pattern of the Scheller antenna configuration - separately for each antenna pair

(the two associated NEC files of my 4NEC2 model are here and here)

That was 1907. Then… nothing much happened with Scheller's invention for several years. Ref. 2C2 suggests that in 1914, the German Imperial Navy used two crossing loop antennas to experiment with a Scheller four-course beacon system. Mid-1906, Franz Kiebitz joined the Kaiserliche Telegraphen-Versuchsamt (TVA, Imperial Telegraphy Test Department, ref. 229A5) of the Reichspostamt, basically the Postmaster General Agency, covering both mail and telegraphy matters - similar to its equivalent in other countries, e.g. the General Post Office in Britain, and the Post Office Department in the USA. During 1909, he supported the rotating beacon tests of the Prussian Building Authority on Müggelsee Lake near Berlin, ref. 187A7. During part of World War I, Kiebitz worked in the Technische Abteilung für Funkgeräte (Tafunk, Technical Dept. of Radio Equipment) of the German army. In the fall of 1917, he began to test the Scheller system with a beam pair directed across and along a winding river and the receiver in a boat. Ref. 229A2. In this 1920 article, he acknowledges Scheller's patent and mentions it was "hardly" tested so far. With Scheller's complementary keying scheme, one of the two antenna pairs is energized at any given time. This led Kiebitz to use three inverted-L antennas instead of two antenna pairs, with one common "L" permanently energized and the other two energized alternatingly - which simplifies commutation considerably. The vertical parts of the L's were close together and the horizontal parts in a star configuration. He also used a 3-pointed star configuration with two pairs of inverted L-antennas, forming 80°/100° angles when looking down on it. He observed the effect of the crossing-angle on the beam width, as illustrated in Fig. 71 above. He was aware that two crossing loop antennas could be used, but he deemed his own antenna configurations simple and reliable. Intital tests were done with a small spark gap transmitter, later tests with a 150 W vacuum tube transmitter and frequencies of 375-860 kHz (350-800 m wavelength, i.e., medium wave). Kiebitz used A/N keying - the first to do so. This was done with a motorized cam wheel and spring-loaded contacts. Ranges up to 180 km (≈110 miles) were obtained, with clear equi-signal zones. Kiebitz was one of the very first to observe and record the so-called shore-line "beam bending"effect. This is refraction ( = change in direction) of electro-magnetic waves (incl. radio) when crossing a land-water interface. It is caused by differences in electrical conductivity, temperature and humidity of land vs. water/sea, and is frequency dependent. The tests with the boat confirmed the ability of the equi-signal beam to mark a narrow course line, and allow detection of deviation from this line. During the period spring-1917 to November 1918, the Flieger-Funker-Versuchsabteilung der Flugzeugmeisterei der Fliegertruppen (FTVA, radio test dept. of the aircraft establishment of the flying corps) conducted many directional radio tests, including with Kiebitz's beacon. Ref. 229A1, 229A3, 229A4. They were inconclusive, due to unexpected phenomena. Very significant, altitude dependent course errors were introduced by the directional characteristics of the receiving antenna-wire that was trailing behind the aircraft. Due to the operating wavelength, such antennas were physically long (e.g., 60 m = 200 ft, ref. 185T1). This undesirable effect was confirmed several years later (1923) in the USA (ref. 229E). A so-called cone-of-silence was also observed while overflying the beacon. Ref. 184L, 229A1, 229A2, 229A3, 229A4, 229G.

Bottom line: Kiebitz was basically the first to build 4-course Scheller equisignal beacons and test them with a boat and an airplane. He also was the first to confirm the effect of the antenna pair crossing-angle on the equi-signal beam width, to implement motorized complementary/interlocking transmitter/antenna keying, to discover shore-line beam-bending effects. The test also were the first to lead to reporting and analysis of course errors due to using a long trailing wire antenna.

During the aftermath of World War I, there was no immediate urge in Germany to continue Kiebitz's activities. Also, the rather French-biased "Peace" Treaty of Versailles, signed 28 June 1919, imposed severe restrictions and reparations. Note that Germany made the final World War I reparation payment to France on 3 October 2010 (!). Part V Section III of the treaty covers "Air Clauses". In particular, Articles 198, 201, and 202 state that the armed forces of Germany must not include any military or naval air forces, and that no dirigibles shall be kept. Furthermore, all military and naval aeronautical material, incl. all aircraft [FD: i.e., airplanes, seaplanes, airships/dirigibles, balloons], whether complete, or being manufactured, repaired, or assembled, are to be handed over to the Governments of the Principal Allied and Associated Powers. Also, for a period of six months, the manufacture and importation of aircraft, parts of aircraft, engines for aircraft, and parts of engines for aircraft, shall be forbidden in all German territory. The implementation of the articles was under control of the Inter-Allied Commissions of Control. It was this CoC (i.e., not the Treaty as such) that subsequently imposed additional orders and rulings during the aforementioned six months period. In particular, the ban on military aircraft production was progressively extended until 5 May of 1922. Performance and other restrictions imposed on civil aircraft and engines actually stimulated the German aviation industry to rapidly become a world leader in aerodynamics, as well as in low-weight engines and constructions (incl. self-supporting structures such as "stressed skin").

Pre-WW1, aviation activity was concentrated in western Europe. E.g., in 1911, it counted almost 25 times as many licensed pilots as the USA (p. 2 in ref. 229W7). This changed after WW1. Especially in the USA, long-distance aviation developed at a high pace, both trans-continental airmail service (ref. 185T3) and passenger air transport. Hence, the need arose for navigation aids for the growing network of routes between airports - in addition to using landmarks and prominent man-made structures such as railroad lines (a.k.a., "steel-beam" and "iron compass" navigation). In particular at night, as the mail service basically worked 24/7. This started in 1919 with bonfires, scattered along the air routes (ref. 229D3, 229F, 229J). In August of 1918, the U.S. Army Air Service handed off the airmail operations to the US Post Office Department (USPO), ref. 229S. Early 1923, the USPO began to construct a transcontinental airway system with optical beacons (enhanced nautical lighthouses). In 1926, this activity was transferred to the brand new Aeronautics Branch of the US Department of Commerce. The first airway light beacon of the Aeronautics Branch entered service in December of 1927. By 1933, about 1500 optical beacons were in place. A standard beacon station comprised a steel lattice tower (standard sizes from 51 up to 152 ft tall, ≈15-46 m), with a powerful 24 or 36 inch diameter rotating-mirror light (500 W or 1 kW), two 18 inch stationary pencil-beam course lights, and an illuminated windsock. Ref. 229R3-No.15. The color of the rotating and stationary light beams indicated whether the beacon served a landing field, a waypoint between landing fields, or an obstruction. Next to the tower was a shack, marked with airway designators on its roof. At remote sites, it housed two gasoline generators (one on standby), activated by a timer or a photocell. A large concrete course-arrow (ca. 70 ft long next to the tower also pointed in the direction of the airway. Ref. 229R3-No.15. The FAA officially decommisioned the last US federal airway beacon in 1973, near Palm Beach, CA.

Optical airway beacons

Fig. 73: Airway Light Beacons and a 5¢ "Beacon on Rocky Mountains" stamp from July 1928 (airmail field near Sherman/WY)

(source left image: ref. 247; center image: Cibola County Historical Society - Aviation Heritage Museum)

The remainder of this section is currently (January 2021) in the process of being overhauled and significantly expanded on a near-daily basis.

Light systems elsewhere, e.g., France and Germany (federal states, Luft Hansa's own network), incl. landing zone projectors, lanterns, smoke pots, etc. As useful as the "light line" systems were, it still required the pilot to have visual contact. During times of reduced visibility (clouds at or below the aircraft altitude, fog, precipitation), no such contact could be established or maintained, or only at close range to a beacon. "Contact flight" = VFR, day or night.

Aero Radio Nav

Fig. 74: Well over a century of equisignal beacons - all directly based on Scheller's inventions

(note: covers fixed-direction, rotable/adjustable direction, and rotating equisignal beam systems)

By 1920, the US National Bureau of Standards (NBS) was seriously involved in R&D regarding "electron" tubes (vacuum tubes, thermionic valves) and radio. The NBS was an agency of the US Department of Commerce, and renamed National Institute of Standards & Technology (NIST) in 1988. This work included cooperation with the Bureau of Lighthouses for a radio-based fog signal system. I.e., just like their German counterpart over 10 years before, see the "Radio Compass" section above. Furthermore, the NBS developed automatic radio transmitter sets for lighthouses, radio compasses, radio direction finders, and the renowned broadcast radio station WWV. This station started in May of 1920 and changed in 1923 to transmission of accurate reference time signals on standard longwave and shortwave frequencies. It is active to this day. Ref 229D12-229D15. Around that time, Percival D. Lowell and Francis W. Dunmore of the NBS worked on loop antennas, designed vacuum tube amplifiers, as well as ship-ship and ship-shore radio communication systems. Ref. 229D14. They also appear to have been co-owners of the Radio Instrument Co., to whom the NBS outsourced work. In 1920, Lowell arrived at the same idea as patented by Scheller in 1907: use overlapping radio beams to create pairs of fixed-direction equi-signal beams. His idea was not pursued at the NBS until another two years later.

Scheller patent

Fig. 7X: "Some degree" of similarity.......

(source: German patent 201496 and US patent 2172365)

By the latter half of the 1920s, it became clear that.... Ref. 229D1-229D15, 229E1, 229F.

  • In US, contrary to Europe, RadNav R&D almost exclusively by various branches of the federal government, instead of private industry.
  • US developments reinvented Schellers system, but US Army Air was fully aware of his patents when they took over ca 1926.
  • Four-Course Range system, Low-frequency Radio Range (LFR) ; a characteristic of the low-frequency range was the Cone of Silence immediately above the station (cf. 3D radiation pattern in Fig. 62 above).
  • Ref. 185F: 22 A/N "signals" [ = characters] per minute [TBC: 22x A + 22x N or 11+11]; interrupted every 15 min for station identification by voice from the omni-directional co-located radiotelephone station.
  • Here, the word "range" is used in the sense of area of open land, e.g., a site for testing equipment. I.e., not in the sense of "distance" (as in the acronym "radar"). Radio ranges do not provide proper distance information, though strength of the received signals (relative field strength) provides some indication of relative distance.
  • "A" / "N quadrant (clean A/N); "A"/"N" twilight zones = bi-signal zone; on-course / equisignal zone; "cone of silence" [add illustration, w/wo "fill in" beacon] over the beacon range ca 100 miles, 1:60 rule of thumb (arctangent of 1° ≈ 1/60) --> 1° triangle --> 1 mile lateral for every 60 miles distance, so a 3°-wide equisignal zone is roughly 3x1=3 miles wide at 60 miles from the beacon, or about 5 miles (4+ NM) at the 100 miles range limit, more difficult to accurately track to course line
  • NBS "cone of silence markers", a.k.a. "Z" markers. First installed experimentally 1934/35, improved 1936/37 by NBS incl. 75 MHz, 3 kHz AM, 7 W. 93 MHz + 60 Hz AM, but 75 MHz for dev of US AAC ILS at Wright Field. Two crossed horizontal dipoles, installed above a ground screen surface.
  • Tests by/at Bureau of Air Commerce, Army:
  • 1923, at National Bureau of Standards Washington/DC: two 1-turn loops, 43.75x15.25m/150x50ft, 36.5°/143.5° crossing angle, 2 kW quenched spark transmitter, A/N, loops tuned to 300 kHz; ref. 229E1.
  • McCook field @ Dayton , ref. 229N.
  • Wilbur Wright field (Wright Patterson), ref. 229N.
  • Typically, multiple airways that lead to/from the same city/airfield/intersection do not cross at right ( = 90°) angles. Also, airway courses are typically also not aligned with north/south and east/west. Therefore, the courses of a Radio Range are typically rotated simultaneously, and bent or shifted (ref. 229Q, pp. 36-43):
  • "course rotation": changing the all courses of a Radio Range by the same amount and in the same direction, i.e., without changing the angles between the course-pairs. (as proposed in Ottos Scheller's patent - most elegantly done with a radio goniometer).
  • "course bending": changing the angle between the two opposite courses of a course-pair, from their normal 180° angle. Typ. by no more than 30°, i.e., to 150-210°.
  • "course shifting": changing the angle between the two course-pairs of a radio range from the standard 90°+90°. Typ. by no more than 30°, i.e., to 60°+120°.
  • The Aeronautics Branch standardized a type of 4-Course Radio Range during the course of 1928.
  • Loop type ranges vs tower (simultaneous voice) type ranges, incl. (dis)advantages: p. 13 ref 229W5.
  • Visual-Aural Range system (VAR), 4-course beacon; a 4-course range, comprising a 2-course Aural Range and 2-course Visual Range; "visual", as it provided on-beam/deviation to the pilot via an indicator instrument, rather than via sound on his headphones.
  • Per ref 185F pp. 37ff: constant tones of diff audio modulation freq, instead of A/N keying. 65 & 86.7Hz (originally 60 & 85 Hz, but abandoned due to....) 86⅔, per ref. 229R4-No.6; originally ) and 75 & 100 Hz. Marker beacons transmitting ID code sigs , primarily to ID intersections of courses from adjacent ranges, "double frequency" marker beacons, alternating between the two. Single -freq beacons used to mark emergency landing fields, abrupt terrain elevation changes, dangerous landmarks; 5 miles max range. Marker beacon freq same as associated Radio Range freq. Marker stations also low power radiophone station, for emergency communications or emergency WX broadcast. Air nav facilities operated on freqs 237-285 kHz (LW) and 315-350 kHz (MW), with 6 kHz channel spacing.
  • Note: per Article 5 of the Regulations of the 1927 "International Radiotelegraph Conference" that took place at Washington/DC, the 285-315 kHz band (ca. 1050-950 m wavelength) was exclusively allocated to radio beacons, effective 1 January 1929. The 237-285 kHz segment was part of the 194-285 kHz band that was shared by Air Mobile Services, Air Fixed Services, Government Fixed Services, and broadcast (in Europe only).
  • one Visual Range system with two course lines (150 Hz and 90 Hz tones, visual indicator in the cockpit, full meter needle deflection for ≥ 10° off-beam deviation)
  • one Aural Range system with 2 course lines (1020 Hz A/N system); equi-signal beam appr. 1½-2° wide.
  • First demonstrated in 1937 by the Bureau of Air Commerce (VHF, 63 MHz), operational in the US from 1944 - 1960 (VHF, 112-118 MHz).. Also used in Australia, operational 1947 to at least 1980
  • Lorenz' 1938 Swiss patent 206464: Motorized rotating antenna arrangement of 2 pairs of vertical antennas (grounded monopoles or dipoles) at corners of a square, Adcock arrangement, simultaneously fed by transmitter via , central vertical monopole, fed simultaneously by same transmitter; creates rotating equi-signal beams; using shortwave to obtain long range.
  • Lorenz A/N AFF, "blind landing system"
  • adopted in Britain via Lorenz/ITT as the Standard Beam Approach System (SBAS) - indeed, it was.
  • Using a separate glide path/slope equisignal beacon was patented by Ernst Kramar (Lorenz) in 1937 (German patent 734130, and equivalent 1939 Kramar/Hahnemann (Lorenz) US patent 2210664). A variation with a separate Lorenz beacon abeam the touchdown zone was patented in 1940 by Andrew Alford (IT&T, parent company of Lorenz, US patent 2294882).
  • ILS (Localiser & Glideslope), SCR51: by ITT, parent company of Lorenz.

"Such equisignal course lines are established by the radiation of directional fields, each of which is identified by a characteristic tone modulation (AM) or signal (keying rythm), and which fields overlap or intersect in space to produce zones of equal signal intensity, which provides the beacon course [or courses]"

BoS loop antennas

Fig. XX: Rotable square loops, hinged on telegraph poles at "compass house" near the Radio Building of the Bureau of Standards

(sources: Fig. 4 in ref. 229E1 (image left), p. 151 in ref. 229D15 (image right); note rotable RDF loop antenna on the roof)

Next Figure: the experimental Aural Radio Beacon station at College Park/MD/USA.College Park is located about 13 km (8 miles) eastnortheast of the Bureau of Standards in Washington/DC, and about the same distance northeast of the White House. Triangular antennas in two crossing vertical planes [crossing vertical Delta-loops], replacing the square loop "coil" antennas. Goniometer was housed at the base of the 70-foot wooden tower. From 1918-1934, the National Bureau of Standards (NBS), the U.S. Navy, the Post Office, and other government and private organizations regularly used College Park Airport to design and test "blind flight" systems. By 1930, a very similar station was installed at Mitchel Field, on Long Island/NY, just outside Hampstead and Garden City (not to be confused with Mitchell Field); ref. 235U3 (p. 24).

1930-01-19 College Park: used in 1909 by Wright brothers for experiments, first Army flying school opened here in 1911, used by Post Office Dept. for first experimental air route starting 12 Aug 1918 and used field until 1921. DoC/ BoS used field for various purposes, incl. range beacons.
1927-35: First radio navigational aids developed and tested by the Bureau of Standards.

BoS loop antennas

Fig. XX: The experimental "Directive Aural Radio Beacon" station of the Bureau of Standards at College Park/MD/USA - ca. 1930

(source image: adapted from Fig. 6 in ref. 229V and Fig. 2 in ref. 229D3; also see Fig. 19 in ref. 229L8 & p. 154 in ref. 229D15)

The wooden tower of the beacon at College Park was 70 ft tall (≈21 m) and painted dark yellow. At the base it was 10 ft wide. The radio room measured 10x14 ft (≈3.3x4.3 m). The two orthogonal single-turn triangular loop antennas spanned ca. 2x150=300 ft (≈90 m). Total wire length per loop was 628 ft (≈190 m). The horizontal wires that ran back to the radio room, were suspended 8 ft above ground by three posts on each side of the mast. Ref. 229Y.

BoS loop antennas

Fig. XX: The inside of the radio room of the beacon at College Park/MD/USA - official inauguration on 30 May 1927

(source: adapted from ref. 229V3; the person in the photo is George K. Burgess, Director of the Bureau of Standards)

4-course radio range

Fig. 74: The 2-loop "polydirectional" 4-Course Range at Wayne County Airport near Detroit/Michigan/USA - ca. 1930

(source: Fig. 11 in ref. 185F; also Fig. 30 (photo) & 31 (dimensions) in ref. 229L14; loops at right angles)

4-course radio range

Fig. xx: Four-course patterns of the Scheller-array for various parameter settings

(source: adapted from ref. 229M)

A/N system

Fig.XX: Aerial view of the Four-Course Radio Range at Elizabeth City NC/USA

(source: Fig. 3 in ref. 229W3 (1940) & 229W4)

"Radio range" beacon : a directional radio beacon that transmits in such a way as to mark out a fixed straight line / provide radio-marked courses (as for directing the course of airplanes to or from a landing field). Here, the word "range" has nothing to do with "distance".

Types RA, RL, MRA, MRL, ML (ref. 229R10).

The following audio clip is the realistic simulation (incl. keyclick suppression) of the receiver sound that would be heard when being on the "A" side of the equibeam of a Four-Course Radio Range AN-beacon. The "N" signal is also heard, but much weaker. As it is complementary to the keying of the "A" signal, it sounds like a continuous background signal. In the middle of the clip, there is a 3-letter Morse code identification (here: ABC), transmitted sequentially on the "A" and "N" beam. Tone frequency is 1020 Hz.

Four-course AN beam sound...

Audio simulation for the A side of an LF Four-Course Radio Range, while also receiving the (weak) N-beam signal

(source: "LF Range Navigation Sound 70% "A"" © Bob Denny, accessed 27 March 2020)

Scheller-Lorenz A/N beam sound - audio file still to be created...

Simulated sound of crossing an A/N beam back & forth and approach beacons - TBD!!!

(source: © ipse)

4-course radio range charts

Fig. XX: Growth of the Radio Range network in the Contiguous USA - 1932, 1935, 1940, 1944

(sources: Fig. 1 in ref. 235P5, Fig. 31 in ref. 229W1, Fig. 46 in ref. 229W2, Fig. 72 in ref. 229W3, Fig. 147 in ref. 229W4)

"Visual-type": vibrating tuned reeds, placed side-by-side, and tipped with a white metal strip about 3/32 x 5/32 inch (≈ 2.4x4 mm). Ref. 229D1, 229D9, 229D10, 229D18, 229D26, 229L13. NBS tested a "vibrating reed" visual radio beacon indicator in 1927.

4-course radio range

Fig. 75A: The tuned-reed course-deviation indicator - construction details

(sources: left image: ref. 229V4, 1928; center: ref. 229R2-No4; right: adapted from ref. 229R1-No22)

"When [the] receiving two tones, the reeds vibrate and move the tips in rapid vertical vibrations, forming what appears as two "ribbons" and varying in amplitude according to the strength of the received signals. When the aircraft is "on course", both ribbons or "reeds" are of equal amplitude. If the aircraft moves "off course", - "longest reed shows side off course" - head A/C towards in direction of the shorter reed to get back on "on course" " [iff flying TO!!!]. relative length diff is measure for cross-track error, ref. The instrument has a TO/FROM "reversing switch", to ensure deflection of the pointer is in the same direction as deviation of the aircraft from the course. Ref. 229R4-No.06

4-course radio range

Fig. 75B: The tuned-reed course-deviation indicator for the 2-Course Visual Range

(source: adapted from ref. 229V; note: reed indication is independent of airplane heading / nose pointing direction!)

The 4-course system can be expanded to a 12-course system, not by adding a third loop antenna with the figure-of-eight radiation pattern (or a thrird vertical antenna pair) instead of two, but by coupling a third transmitter chain to the existing loop pair. ref. 229R1-No.4, 229D1, 229D15 (p. 157): antenna system still comprises two crossing loops, as with the 4-course system, but goniometer with 3 stator coils spaced 120°, one connected to each PA of the TX (now 3 PA's and modulators), 2-coil rotor as before. Tested at College Park/MD. Shifting courses per 4-course beacon method, or - less complicated in the 12-crs system - displacing the stator windings from their normal 120° positions.

Rather than Visual Range with its two tones (65 Hz & 86⅔ Hz), now three different constant modulation tones were used: added 108⅓ Hz. Clearly, the deviation indicator and associated electronics also had to be adapted, ref. 229D1, 229D9, 229L7. E.g., reed instrument with 3 reeds (since 3 audio freqs), but 4 tabs, such that any pair of freq could be selected by sliding shutter/mask. So, always selecting one of 3 4-courses (red/black, green/amber, blue/brown). Actual airway beacon(s) actually ever implemented? No!

12-course radio range

Fig. 75C: The 12-course radio range pattern and prototype TO/FROM rotable reed instrument

(source left image: adapted from Fig. 3 in ref. 229D9; right image: adapted from 229V4, 1928)

12-course radio range

Fig. 75D: The 3-reed cockpit instrument for the 12-course radio range

(source: adapted from Fig. 1 & 2 in ref. 229D9 and Fig. 25 in 229D3)

4-course radio range

Fig. XX: Blind Landing System - instrument panel of test airplane of the National Bureau of Standards, 1930

(source: "Blind Landing of Aircraft collection" of National Institute of Standards and Technology (NIST) Digital Archives)

WW2: also US mobile (truck mounted 4+1 "TL" antenna config) military VHF (100-156 MHz) 2-CRS A/N aural radio range system for ldg field or waypoint marking, w periodic sector ident via D/U keying, w simultaneous voice capability (e.g., AN/MRN-2, p. 38 in ref. 230U2), with ...

The US/NBS used the patented Yagi-Uda VHF beam antenna design (p. 161/162 in ref. 229D15).

VHF Glide Path antenna

Fig. XX: Experimental VHF Glide Path antennas - Bureau of Standards (left, center) and, "inspired" by it, of the German DVL (right)

(source left-to-right: ref. 229D15 (1928/29, 93.7 MHz), ref. 235Y4 (1930, 100 MHz, dipole + reflector + 6 directors); ref. 2 (1931, 63-64 MHz, 5 directors))


In 1924/25, Shintaro Uda - engineer and assistant professor at Tohoku Imperial University in Japan - invented a highly directional multi-element antenna system. During 1925-1929, he published his research in about a dozen articles in the Journal of the Institute of Electrical Engineers in Japan. In 1926, he co-published a first article outside Japan (USA, ref. 18D) with professor Hidetsugu Yagi, who only had a subordinate involvement in the actual R&D. The latter article also proposes to use this type of antenna for directional radio beacons. In December of 1925, Yagi patented the antenna system in Japan (69115), listing himself as the sole inventor. In 1932, Yagi filed a similar patent in Germany (475293) and in the USA (1860123). The latter has Radio Corp. of America (RCA) as the patent assignee/owner. RCA was the Marconi Wireless Telegraph Company of America ("American Marconi") until it was acquired by the General Electric Co. in 1919.

Eversince, this type of antenna system is commonly referred to as a "Yagi-Uda" antenna, or even worse, just "Yagi" antenna.... Ref. 18A-18C.

In its simplest form, the Uda "beam" antenna is a 2-element antenna. It has a single radiating element that is "driven", i.e., is connected to a transmitter (or receiver, or transceiver), and a single passive element. The latter is not driven. Typically, the driven element is a simple standard 1/2 wavelength resonant dipole. The passive element is a mono-pole: basically a rod that is slightly longer or shorter than the driven element. This element is placed at some distance (typ. 0.1 - 0.25 wavelength) to, and in parallel with, the driven element. The two elements are electro-magnetically (EM) coupled: EM radiation from the driven element induces current in the passive element. This way, the passive element "feeds" on the driven element. This is why the passive element is also referred to as a "parasitic" element. In turn, the induced current is partially re-radiated by that passive element.

yagi uda

Fig. 2A: Principle of a 4-element Yagi-Uda antenna

(source: wikipedia.org; D = director, R = reflector, E = excited/driven element; look closely: the green wave emanates from E, the red, blue, and pink waves from R, D2, and D1, respectively)

The waves that are radiated by both elements, combine in all directions - they are superimposed. This results in a 3-dimensional interference pattern around the antenna. Due to the spatial distance, there is a phase delay between the radiation from the driven element, and the re-radiation by the passive element. If the passive element is slightly longer than driven element (typ. by about 5%), then its radiating current lags the voltage that is induced in this element by the driven element. Consequently, the waves of the two elements combine constructively ( = amplifying) on the side of the driven element that is away from the passive element.

On the passive element side of the driven element, the waves combine in a destructive ( = extinguishing) manner. Hence, such a passive element is called a "reflector". Conversely, the re-radiated current leads the induced voltage if the passive element is slightly shorter than the driven element. Its re-radiation combines constructively on the same side of the driven element as that passive element. Such a passive element is called a "director". The driven element by itself has a radiation pattern that is symmetrical: a torus ("doughnut" shape), with the element poking out both sides of the torus hole. Effectively, a reflector or a director concentrate the energy radiated by the driven element in a particular "beam" direction, by reducing the radiated energy in all other directions. Uda antennas with more than two elements have one reflector and one or more directors, all in parallel. I.e., a linear array. Note that each element is coupled to all other elements: all re-radiations are re-radiated by all other elements, etc. The size and individual spacing of the elements determines how much the radiated energy is concentrated in the forward beam lobe ( = forward gain), how much in the rearward lobe ( = the front-to-back or front-to-rear ratio), side-lobes (if any), the beam width, feedpoint impedance (hence, SWR bandwidth), etc. A standard 3-element beam antenna typically has a forward gain of about 6 dB (4x power factor). In accordance with the universal Law of Diminishing Returns, each additional director N+1 increases the gain relatively less than the adding the preceding director N.

Clearly, on HF frequencies (i.e., below 30 MHz), full-size many-element Uda antennas are impractially large for experimentation and most applications. This is why Uda's experiments focussed on VHF frequencies and above. During World War II, both sides of the conflict used Uda antennas for radio beacons and radar. Since WWII, basically all VHF "FM" radio and VHF/UHF broadcast TV receiving antennas on earth are "Yagi" antennas.

Uda-Yagi examples

Fig. XX: Examples of "Yagi-Uda" antennas

Note that the above antennas are linear phased arrays: all elements are placed on the same base line. The phased array antenna as such was actually invented by Karl Ferdinand Braun in 1905, twenty years before Yagi and Uda! Ref. 186Q2, 186Q3. This was also recognized by Marconi and Franklin in their 1919 Australian patent nr. 10922. Braun's array comprised three vertical monopole antennas, placed at the corners of an equilateral triangle. Two of the antennas were fed in-phase. A 1/4 wavelength phase-delay line could be put in series with the third antenna. By selecting which antennas where fed in-phase or with a phase-delay, the beam could be turned into three directions, spaced 120°.

Phase array antenna

Fig. XX: World's first phased-array antenna and its far-field polar plot - by K.F. Braun, 1905

(source: Fig. 13 & 14 in ref. 186Q2)

Braun also invented the Cathode Ray Tube (CRT, Braun's Tube, D: "Brauns'sche Röhre") and the oscilloscope in 1897. In 1901, he introduced the capacitor-inductor oscillator circuit and replaced literal "grounding" to earth, with a "counterpoise" that was not connected to earth/ground. After several nominations, Braun received the 1909 Nobel Prize in Physics for his contributions to "wireless telegraphy". He shared the prize with Marconi.

LW/MW "Marconi" range in Australia.

Rotating beam system - stationary antennas. Ca. 1928, the C. Lorenz company in Berlin began to use the 1907+1916 "Scheller" patents, which they owned. Interesting aspect: alternatingly connecting the transmitter to the two input coils of the motorized radio goniometer was done with two switches, iron-powder toroidal transformer cores ("Pungs Drossel), each with a DC-powered control winding, driving the core into saturation, causing a high series impedance to the transmitter signal ("Tastdrosselverfahren". lit. "choke-coil keying method"). "Magnetic-bias keying", ref. 229N. A/N sequence. 4-course beacon. Rotable, not rotating. Before NBS in USA. Lorenz test site at Versuchsfunkstelle Eberswalde (on the Finow canal, about 48 km, 30 miles, northwest of down-town Berlin). Freq: 385 kHz, long-wave 780 m wavelength, 800 W transmitter power. In 1931/32, goniometer motorized, to get a rotating beacons. "Umlaufende Richtfunkbake Eberswalde". Range ca. 350 km. But two crossing loops antenna system, instead of Scheller's 2 pairs of vertical antennas (copied by Adcock), hence, limited use due to sky wave night-effect. Ref. 2A. Note: same approach with "DC transformer" / "saturating transformer" was standard high-power light dimmer device for (movie) theaters etc. for many decades.

In 1913/1914 Leo Pungs and Felix Gerth (both at C. Lorenz AG) developed the first practical and satisfactory method for amplitude modulating the RF antenna current of high power transmitters with voice and music. It used a choking coil on a closed laminated iron core. The series-impedance of that coil was controlled by varying the magnetic saturation level of the core via the DC current through a secondary coil on the same core. This was referred to as a "telephony choke" or "Pungs choke" ("Steuerdrossel", "Pungs-Drossel"). The concept was originally proposed by Reginald Fessenden around 1902, who never got it to work properly. In 1913 Ludwig Kühn of the Dr. E.F. Huth company in Berlin revived the method (cf. 1923 US patent nr. 1653859). By hard-switching between zero and full saturation, this type of choke coil could also be used as an on/off telegraphy keying-choke ("Tastdrossel"), i.e., as an RF switch, instead of an AM modulating choke.

Lorenz LW rotable beacon Eberswalde

Fig. 76: The experimental Lorenz long-wave rotable/rotating four-course A/N beacon at Eberswalde/Germany

(source: adapted from ref. 2)

Lorenz LW rotable beacon Eberswalde

Fig. 76: The experimental Lorenz long-wave rotable/rotating four-course A/N beacon at Eberswalde

(source: ref. 2)

By 1920, 98% of the C. Lorenz AG company shares were owned by the Dutch firm N.V. Philips' Gloeilampenfabrieken. In 1930, they were acquired by Standard Elektrizitätsgesellschaft, a subsidiary of the US American International Telephone and Telegraph Corporation (ITT, also IT&T). Ref. 263A-263C. ITT was created by the Puerto Rico Telephone Company (Ricotelco) in 1920. From 1922 through 1925, ITT acquired all overseas subsidiaries of Western Electric, and a number of European telephone companies through its subsidiary C. Lorenz AG. This included Standard Telephones & Cables Ltd (STC) in Britain, Standard Elektrik Lorenz (SEL) in Germany, Bell Telephone Manufacturing (BTM) in Belgium, and Compagnie Générale de Constructions Téléphoniques (CGCT) in France. See Figure ????? below. The A.E.G. Telefunken company also had affiliations with a major US American conglomerate: International General Electric (IGE). Their facilities were not bombed during WW2, other than accidentally. They were actually on American "do-not-bomb" lists, as were e.g., the Ford Motor Co. facilities. Note that Siemens (as was Brown Boveri) had no close ties with US companies. Their production sites were the specific target of Allied bombing raids. Ref. 8.

During 1932/33, Ernst Kramar of the Lorenz company applied the concept of the Lorenz-Scheller A/N-system to a "blind landing system" for aircraft. Ref. 28, 188, 235C2, 235C3. Note that "blind landing" [or, more generally, "flying" = "solely by reference to instruments"] is somewhat of a misnomer, as the system did not provide precision vertical guidance down to the actual touch-down of the landing phase. Hence, it is only an approach-beacon (D: "Ansteuerungsfunkfeuer", AFF). These days, we would refer to this beacon as a non-precision "localizer" approach system: the horizontal ( = lateral) component of an Instrument Landing System (ILS).

As discussed above and shown in Fig. 60/61, the ground-station of the Scheller system had a radiation pattern with four main lobes, in fixed orthogonal directions. See Figure 41A. Two of the lobes transmitted the Morse code letter "A", the other two the letter "N". Where lobes overlap and are of equal strength, the combination of "A" and "N" results in a constant tone signal, the so-called "equi-signal". This signal had a beam width of about 1-5°. This was the first "A/N" system, later used in several other Lorenz radio-navigation systems. Subsequent variations of this scheme used narrow "A" and "N" beams, with a much narrower overlap, allowing more accurate determination of the course line of the equi-signal. In the 1907 Scheller patent, the directional radiation patterns are obtained with four equidistant vertical antennas.

A-zone (≈10-15°), bi-signal / "twilight zone" (≈2x15°, A dominates in one half , N in the other), equi-signal/on-course zone (≈1-5°), N-zone (≈10-15°). For visual-type radio range beacons, the 65 Hz tone beam corresponds to "A" and 86⅔ Hz to "N". Ref. 229R7-No. 6.

The antenna system is very simple: a vertical exciter dipole of standard length (½ λ), with a vertical reflector to the left and to the right. See Figure 77. This system was patented in 1932 by Ernst Kramar of the C. Lorenz AG company in Berlin (Reichspatent 577350, British patent 405727). The dipole is excited continously by the transmitter. The reflectors are completely passive: they are never connected to a transmitter. Each reflector can be "opened" at its mid-point with a relay. This reconfigures the reflector into two unconnected half-length rods - much too short to affect the radiation pattern of the active dipole. The two relais are energized in a interlocked fashion: when the contact of the Relay 1 is open, the contact of Relay 2 is closed, and vice versa. This makes it very easy to implement complementary keying (E/T, A/N, etc.). Note: a driven dipole + passive reflector rod is the simplest form of the 1925 Yagi-Uda beam antenna.

Ref. 185H, p. 12 ff. 1932 flight tests at Berlin-Tempelhof.

Ref. 235Y4, The constant-intensity glide path proposed in 1929, BoS/Diamond & Dunmore.

1938 Lorenz' Swiss patent 206463: standard Lorenz landing beam arrangement with only a single switched refelector.

Lorenz-Schiller A/N system

Fig. 77: The antenna arrangement of the Lorenz-Scheller E/T localizer beam ("Lorenz Beam")

(source: ref. 31)

The patents covers a distance of 0.2 - 0.5 λ between dipole and reflectors, which primarily affecting sharpness of the beam. The patent also considers reflector length shorter/same as/longer than the dipol. This primarily affects side lobes. For a parallel rod to work effectively as a reflector, its electrical length must typically be within 5-10% of length of the dipole.

Kiebitz vertical dipole

Fig. 78: Radiation pattern of a vertical dipole with one reflector to the left of it

(cases similar to those covered by Ernst Kramar's patents RP577350 & GB405727; note: radiation patterns are for "free space" case = without ground)

Lorenz-Schiller A/N system

Fig. 79: The beam pattern of the Lorenz beam - simulated vs British patent 405727

(source: ref. 31)

The signal transmitted by the dipole induces current into the parallel reflector. In turn, this induced current causes the reflector to (re)radiate. This radiation combines with that of the dipole. Depending on the distance ( = phase) between dipole and reflector, the strength of the dipole radiation is decreased in directions behind the reflector, and increased on the opposite side of the dipole. I.e., the radiation pattern of the dipole is no longer omni-directional. Basically "vertical 2-element beam" antenna. How the antenna works. The radio waves from each element are emitted with a phase delay [physical distance + inductive-lag=long=reflector/capacitive-lead=short=director], so that the individual waves emitted in the forward direction are in phase, while the waves in the reverse direction are out of phase. Therefore, the forward waves add together, (constructive interference) enhancing the power in that direction (constructive interference / EM wave combination)), while the backward waves partially cancel each other (destructive interference), thereby reducing the power emitted in that direction. At other angles, the power emitted is intermediate between the two extremes.

Two overlapping "Scheller" beams with equisignal zone:

  1. Complementary keying with same tone frequency + aural assessment of audio signals and equisignal. No viusal indicator.
  2. Same, with additional visual indication with a galvanometer instrument with needle that "kicks" to left or right in the rhythm of pos & neg induction pulses that are derived from the leading / trailing edges of the keyed tone pulses, with the inductance of a transformer; hence, impossible to make accurate reading of needle deflection and also requires simple dot/dash keying patterns.
  3. Both beams transmitting continously, each modulated with a different tone frequency + visual indication of the relative signal strength of the received tones; no aural assessment possible (e.g., when pilot performing other tasks). Indicator can be tuned reeds, or galvanometer needle-instrument, with summed rectified demodulated tones, one of which with inverted sign.
  4. Combination of 1 & 3: complementary keying with two tones + aural of tone pulses + visual of the relative strength of those pulses. Aural & visual indications cannot be guaranteed to be consistent.
  5. TBC: like 2., but with with galvanometer needle-instrument instead of kicking meter, TBC conversion of tone or inductive pulses. Patent?

Kramar's 1937 patents expand this scheme with a complementary-keyed (e.g., E/T) beam system for vertical guidance. This [the latter?] was simply re-patented in 1940 in the USA by others (e.g.,...ITT?)

front course, back course - revert L/R mentally or switch instrument of switch beam keying when active crs changed.

Insrtument localizer: front/forward course beam that enables approaching aircraft to establish lateral alignment with the runway / runway centerline.

In 1934/35, Telefunken developed their version of the Lorenz AFF/VEZ/HEZ "Landeleitstrahlanlage" system (ref. 2A, 235A), to Lorenz specifications.

Lorenz Localizer ET-beam

Fig. 79: Telefunken and Lorenz localizer-beacon ground stations

(sources: ref. 2 & 235A (left, Telefunken), ref. 31 (center), ref. 137B / 225C2 / 235P26 (Lorenz, at Berlin-Tempelhof airport))

Lorenz Localizer ET-beam

Fig. 80: 1937 Lorenz beacons - left & center: at Zürich-Dübendorf/Switzerland airport, right: at Heston/Middlesex/UK aerodrome

(sources: ref. 235B (left), ref. 137B (center), ref. 235P6 (right))

Lorenz beam station

Fig. XX: Typical dimensions of a Lorenz beam ground station

The two reflector dipoles were activated alternatingly, to deform the dipole beam slightly to the right and to the left. This effectively created a directional beacon ("Richtfunkfeuer") with a twin-beam radiation pattern. At the centerline of the beams (aligned with the centerline of the runway), the "E" and "T" beams would merge into an 1150 Hz equi-signal zone that had an aperture of about 5 degrees. The antenna system was located at the far end ( = departure end) of the runway, so as to provide left/right guidance throughout the entire approach, landing, and roll-out. During approach to landing, the arriving aircraft would intercept and track the equi-signal beam. The beam-system operated at frequencies in the 30 - 36.2 MHz range (λ ≈ 10 m). The pilot would hear the E/T audio signals, and also have a Left/Right course deviation indicator.

A marker-beacon ("Einflugzeichenbake", EFZ-Bake) was installed on the extended runway centerline, at two fixed distances from that runway: an Outer Marker ("Vor-EFZ") at 3 km, and a Main Marker ("Haupt-EFZ") at 300 m, ref. 32. These beacons transmitted on 38 MHz, with a narrow upwardly pointing fan-beam, extending across the approach course and at right angles to it. This allowed the pilot to determine when to initiate descent to the runway from a standard altitude and with a standard descent rate (ca. 3 degrees flight path). Ref. 26B, 235L1-235L5.

Lorenz Localizer ET-beam

Fig. 81: Lorenz VHF marker beacons - horizontal dipole above a "chicken wire" ground screen and a transmitter "dog house"

(source left image: ref. 254 (taken near Berlin-Tempelhof airport; also in ref. 235P44, 235Q); right: Fig. 7 in ref. 235E)

The marker beacon antennas were standard 1/2-wavelength horizontal dipoles. So, for 38 MHz, they had an overall length of about 3.75 m (≈ 12.3 ft). Based on the photos above and below, they were also installed about 1/2 wavelength above the ground. The transmitter was placed in a large "dog house" at the base of the antenna. A chicken-wire ground plane of ca. 3.5x8 m extended about 1/2 wavelength to the left and right of the dipole. It shielded the transmitter and also made the antenna's radiation pattern less dependent on the local soil conditions. The dipoles were aligned with the runway's centerline.

Lorenz Localizer ET-beam

Fig. 82:  VHF marker beacons - Lorenz  at Grove/Denmark (left) , and AEG/Telefunken equivalent (right)

(source: ref. 235F (left), ref. 2 (Telefunken))

This "Lorenz beam" system entered service in 1934 with the German national carrier, Deutsche Luft Hansa (a 1926 merger of Deutsche Aero Lloyd and Junkers Luftverkehr; "Luft Hansa" became "Lufthansa" at its post-WW2 re-start in 1953). It was subsequently commercialized worldwide.

Lorenz beam landing procedure

Fig. XX: Schematic depiction of the Lorenz "bad weather" landing procedure

(source: adapted from ref. 31)

Demonstrated to the US Army in 1932. Ref. to be added.

"Funknavigationsanzeiger" of „Lorenz-Blindlandungs-Empfangsanlage für Flugzeuge“

Lorenz instruments

Fig. XX: 1936 side-by-side indicator made by C. Lorenz AG and equivalent instrument by AEG-Telefunken

(AEG-TFK was licencee of the Lorenz system; source image right: ref. 235C, also 235P4/P26; image left: unedited image courtesy B. Justusson)

Lorenz instruments

Fig. XX: Ca. 1936 landing beam indicators made by C. Lorenz A.G. and a WW2 Type 3 Mod. S-47 by Sangamo Weston Ltd.

(sources - left to right: ref. 235P41; ref. 235Y4 (also 229L20, 235Q, 235P7/P8/P18, 254); aeronautique.com (accessed August 2020))

Fig. XX above: in January of 1938, Sangamo Weston Ltd. received a contract from the British government to manufacture a copy of the Lorenz Beam Approach Indicator, ref. 235D, 235P17.

To have same interpretation of left/right meter deflection on both of the two opposite-direction equi-signal course lines, Lorenz' 1935 patent 180996 proposes to install outer & inner marker beacons on both front- and back-course, but inversed the keying of the reflectors, based on which of these two courses is in use.

corporate Lorenz ITT ATT

Fig. XX: Overview of the intertwined history of the Lorenz, ITT, and STC companies in volved with ILS

(note: this overview is quite simplified, e.g., 1960 to 1977, ITT acquired more than 350 companies)

the LORENZ "kicking meter" CourSE-Deviation indicator SYSTEM

As stated before, the two overlapping beams of the Lorenz system were modulated with a 1150 Hz audio tone. The pilot/navigator interpreted the resulting tone signals via the audio in the headphones, to determine lateral (i.e., left/right) deviation from the equisignal course line of the beacon. Clearly, it was highly desirable to also have a visual indication of that course deviation. This required conversion of the pulsing audio signals from the radio receiver, to electrical signals for driving an indicator instrument.

This conversion is done in several stages, see the next Figure. First, a transformer electrically isolates the actual conversion circuitry from the potentially high voltage at the audio output of the receiver. At the same time, this transformer prevents the low impedance of the next converter stage from overloading the receiver's output. Next, a bridge of four solid-state diodes rectifies the tone pulses. The amplitude of the resulting DC-pulses toggles between two levels. These levels correspond to the relative strength of the interlocked tone pulses. If both pulses are equally strong, the rectifier output is a constant DC voltage, equivalent to the strength of the received equisignal. A capacitor is used to smoothen the audio ripple on the DC pulses. The inductance of a second transformer is used to differentiate the DC pulses: a rising edge results in positive induction pulse, a falling edge in a negative induction pulse. These pulses exponentially decay to zero. Two diodes in anti-parallel configuration are used to limit the amplitude of the induction pulses, so they do not reach a level that would damage the downstream meter. The limited induction pulses are fed to a moving-coil meter. A "zero-center" meter is used, so as to be able to indicate both pulses with positive and negative polarity. The needle's resting position is at the center of the meter scale. The equisignal contains no tone pulses, hence no DC or induction pulses are generated, and the meter needle does not deflect at all.

kicking meter signals

Fig. XX: Conversion of interlocking tone pulses to needle deflections in the Lorenz "kicking meter" indicator system

(source: adapted from ref. 2A, 2C2, 32, 230F, US patent 2290974; signals shown for aircraft slightly to left of inbound approach course)

The next Figure shows the signals for "E/T" keying of the two overlapping beams ( "E" = Morse "dot ", "•", "T" = "dash", "─"). This was the initial Lorenz-beam keying scheme, and also used in the Telefunken Knickebein beam system of the German Luftwaffe in WW2. It is, in fact, the simplest possible interlocking beam-keying scheme. Note that there is a pair of closely-spaced "opposite sign" induction pulses for each "E" tone pulse. Conversely, there is a widely-spaced "opposite sign" induction pulses for each "E" tone pulse. The needle of a normal moving-coil meter would respond to both pulses of each such pulse pair. Such a meter would just vibrate about the zero position, which would be completely useless. This is why a special moving-coil meter had to be used. Its permanent magnets were shaped so as to create large damping, and meter sensitivity decreasing with increasing needle deflection. With such a special meter, the needle only "kicks" in the direction of the strongest pulse: to the left if the "E" pulse was stronger than the "T" pulse, to the right in the opposite case. The amount of deflection is proportional to the difference in strength between the dominant and the weaker pulse. Due to the pulsating needle movements, the instrument was referred to as a "kicking meter" ("Zuckanzeige"). The system conversion circuitry and meter were dimensioned such that full needle deflection was obtained very close to the course-beacon. For the standard "E/T" keying scheme, the meter kicks once per second.

kicking meter signals

Fig. 82B: Conversion of tone pulse amplitude to "kicking" movement of the indicator pointer

(source: adapted from ref. 2A, 2C2, 72, 230F, 235C, 254)

If you look closely at the shape of the needle deflection pulses in line d of the Figure above, you will see that each such pulse actually has four regions: a steep exponential increase away from zero, followed by a brief slow partial decay back towards zero, then a very short steep partial decay continuing towards zero, and finally a long slow decay all the way back to zero. In all, the meter's needle movements were rather "nervous", which made it inherently difficult or impossible to accurately read the amount of deflection.

Note that, without additional electronic circuitry, the above tone pulse conversion scheme only works with the interlocked "E/T" keying scheme, i.e., with one beam only keyed with "dots", and the other only with much longer "dashes"! Practical tests (e.g., in Britain, of the German Lorenz beam system) showed that aural interpretation is better with complementary dots-and-dashes keying patterns, where both characters have the same number of dots and the same number of dashes. Examples: "A/N" ("A" = "dot dash", "• ─", "N" = "dash dot", "─ •") and "D/U" keying ("D" = "dash dot dot", "─ • •", "U" = "dot dot dash", "• • ─"). However, patterns other than "E/T" cause induction pulse patterns that always cause alternating needle deflection in both directions, independent of which character is dominant! Luckily, for such complementary keying patterns, the positive and negative induction pulse patterns have a distinct repetition rate. This means that they can be separated with two filters that are tuned to these two repetition rates. The above converter block diagram shows an additional box labeled "Optional filter". It comprises an isolation transformer with two secondary windings, each followed by a simple capacitor/inductor filter and a half-wave single-diode rectifier. Ref. the 1938 US patent 2290974 of Ernst Kramar (Lorenz). With this additional filter, the standard kicking meter instrument can be used with keying schemes other than E/T.

Note that when no signals are received (e.g., due to receiver failure), there is no meter deflection - just like when flying exactly on the equisignal course line. Hence, monitoring the audio for presence of the equisignal or tone pulses was advised.

Note that the "meter sensitivity decreases with increasing needle deflection" characteristic also had the advantage of making small deviations from the equisignal course-line a bit more evident.

The above convertor shows that using keyed beam signals is not quite as simple as comparing the relative amplitude of two continuous audio tone-frequencies.

Note the A/N Radio Ranges in the USA were "aural" only.

1937: Approximately 35 Lorenz ground equipments have been installed in various parts of the world, 14 of which in Germany, and about 200 receivers installed in planes engaged in air transportation in various countries. Ref. 229L20. By 1938, some 38 of these beacons were installed at airports throughout the German Reich. The above beacon provides lateral ( = horizontal, left/right) guidance. In 1937, Lorenz/Kramar created a separate system for providing vertical approach-to-landing guidance, by turning the antenna system 90 degrees and placing it next to the runway, abeam the touch-down point. The combined system with lateral- and vertical-guidance beams is called Instrument Landing System (ILS). It is used to this day. For a general treatise of such beam systems by Ernst Kramar himself, see ref. 254 (1938).

Installed and demonstrated by Lorenz at Indianapolis/MD airport in 1937. Ref.229L19, 235P37, 235P47, 235Z2, 235Z3, 235Z5.

In 1936/37, Lorenz installed its beam systems at three aerodromes around London: Croydon, Heston, and Gatwick. Sept 1936: operational at Heston, decided to proceed with installation at Croydon, order placed for installation at Gatwick; all installed by STC. Ref. 235B2, 235P6:

In response to the need for long-range radio navigation, the Lorenz company investigated and developed a long-range course beacon, based on its standard VHF landing beacon system. Throughout the 1930s, propagation of VHF radio waves (frequencies 30-300 MHz) beyond visual range had already been extensively investigated and reported in publications in the USA and Germany (e.g. by the "DVL Deutsche Versuchsanstalt für Luftfahrt" (DVL, German Aeronautics Research Institute), ref. 229L21 and publications referenced therein). 1937 Lorenz tests at Essendon (installed by its ITT sister-company STC Pty. Ltd.), standard Lorenz beam antenna config (i.e., dipole+2reflectors), 30 m wooden tower, with 500 W transmiter, 9 m wavelength [European standard 33.3 MHz beacon freq]. Results so favorable that decided to plan intro in AUS of a network of VHF beacons instead of long-wave beacons, potentially with an additional reflector pair to create VHF 4-course beacons.

Lorenz UKW Bake installed at Essendon Airport (Melbourne/Australia) by Lorenz (p. 96, 97 in ref. 2), 1937; Kastrup/Denmark, 1937, Malmi-Helsinki 1937 (see advert-TFK-AEG-ILS-Finland-Aero-Vol17-193709.jpg).

Lorenz AWA

Fig. XX: Lorenz Radio Range beacons in Australia (left to right) - Essendon ca. 1938, Nhill Aeradio Station ca. 1939, Seymour 1944

(source: Civil Aviation Historical Society & Airways Museum/Australia; left-to-right: Essendon (EN), Nhill (NHL), Seymour (SYR))

Lorenz STC Australia

Fig. XX: Advertising for Lorenz beacon equipment by its ITT sister company STC Pty. Ltd. in Australia, ca. 1939

(source: ref. 229P2)

Mobile Luftwaffe version, using same transmitters as the civil version. However, the antennas of the main and the marker beacons are different. The main beacon antenna (the standard "vertical dipole + two switched reflectors" configuration) is scaled down by about 25%, i.e., resonant around 43 MHz instead of 31 MHz. Three variometers are used to adapt them to the 30-33.3 MHz transmitter frequency. For the equisignal beacon, either the 120 watt "AS 2" transmitter was used, or the 500 watt "AS 4".

Luftwaffe AFFA

Fig. XX: "UKW-Landefunkfeuer 120 Watt und 500 Watt" - mobile Lorenz landing beam beacon system of the Luftwaffe

(sources: adapted from ref. 39B-39G)

Introduced into Luftwaffe in 1933? LFF vs Jagd JFFF, see ref. 6F.

Late 1930s (TBC): RAF (below), Plessey, and Marconi landing beam systems  ca 1938. Ref. 235P45 ( = equisignal LOC + 2 markers), ref. 235Z6.

British Royal Air Force - Standard Beam Approach ground Installations (ref. 235V1):

  • Fixed Ground Radio Installation type 5069 (F.G.R.I.5069):
  • Transportable Ground Radio Installation type 5041 (T.G.R.I.5041):

The F.G.R.I.5069 comprises a main beacon transmitter of type T.1345, with the actual radio transmitter equipment installed in a hut. The T.G.R.I.5041 comprised a main beacon transmitter type T.1254, with the equipment installed in a "radio vehicle" trailer. The installation generated 500 watt "aerial power", which presumably refers to radiated power, not transmitter output power. The crystal-controlled operating frequency was in the range of 30.5-40.5 MHz, with standard Lorenz 1150 Hz modulation. The installation consumed 4-5 kW of supply power (220/250 volt, 50 Hz). Power was supplied via a burried cable from the airfield main supply, or by a diesel-electric generator set. A "Type 2" automatic keying device was used with both types of G.R.I. (ref. 235V2). This device comprises two motorized cam discs. The "interval cam disc" interrupted the normal beacon keying every 1, 2½, or 5 minutes for a period of 5 sec max. During this interval, the "code cam disc" keyed the 2-letter Morse code beacon identification, with 1/6 sec dot-length. During ID transmission, both reflectors of the antenna system were disabled, so as to obtain an omni-directional radiation pattern. There was a possible option to operate the main beacon with either E/T keying (dot/dash, Lorenz standard 1/8 sec and 7/8 sec respectively), or A/N keying. The T.1345 and T.1254 superseded the type T.1122. All transmitter types include the associated antennas, cables, etc. A remote control unit and a monitoring arrangement was located in the airfield's control room. It provided switching devices, transmitter status indication, and control of obstruction lights. Associated aircraft receivers are the R.1124A and R.1125A (ref. 235V3, 235V4).


Fig. XX: The "T.R.G.I. 5041" - SBA main beacon trailer and antennas

(source: adapted from ref. 235V1)

Both the fixed and the transportable G.R.I. include two marker beacon transmitters of type T.1295, basically a type T.1123 with an improved radiation pattern. The transmitter generated 5 watt "aerial power" on 38 MHz, with standard Lorenz keyed-tone modulation of 700 Hz (Outer Marker) or 1700 Hz (Inner Marker). The transmitter consumed 150 watt of supply power (220/250 volt, 50Hz). Power was supplied via a burried cable from the airfield main supply, or by a petrol (US: gasoline) generator set. This transmitter system includes two pairs of identical horizontal ½λ dipole antennas - compared to single horizontal dipoles in the original Lorenz system. The dipoles of each pair are spaced by ½λ, and fed in-phase. For the Inner Marker, they are installed in parallel, on either side of the extended approach path / runway center line. For the Outer Marker, they are installed end-to-end in-line (a.k.a. collinear) and on the approach path center line.

AP1186 §104: "The aeroplane should be flown at a constant air speed directly across the beam at a distance of 20 miles from the transmitter and at a height of about 3000 feet."


Fig. XX: "T.1295" - SBA outer marker beacon (left) and inner marker beacon transmitter installations

(source: adapted from ref. 235V1)

The antenna installation of any Lorenz main beacon system transmits a pair of overlapping beams in two opposite directions: the normal approach (a.k.a. "front-course") and the reciprocal approach (a.k.a. "back-course"). The standard pair of marker beacons is placed on the front-course. Inherent to the particular antenna system, the left/right keying on the back-course is reversed compared to the front-course. To be able to use the back-course as front-course, there was a provision for swapping the keying of the overlapping beams. In these cases, the F.G.R.I.5069 or T.G.R.I.5041 included a second T.1295 pair of marker beacons, placed on the normal back-course line.

"T.R.G.I. 5041" vs "T.U. 3" main beacon installation + "M.U. 3" marker beacon installation (ref. 235P14).

Set, Complete, System (not "Signal Corps System"!), model no. 51 ( = SCS-51): TBC designed by ITT Federal Telephone & Radio Corp./Labs, manufactured by ITT Federal Mfg. & Eng. Co.?? ITT being parent company of the Lorenz AG. comprising the following system components [add family tree!]:

  • Localizer:
  • AN/MRN-1 (introduced mid 1942): VHF (108.3-110.3 MHz, 25 W), Basic Component BC-751 localizer transmitter (w BC-752 90/150 Hz modulators & RF bridge) + monitors (BC-753 (fixed) or BC-754 (portable) course detector + BC-755 filed intensity meter + BC-777 indicator alarm; range 40/70/100 miles at 2500/6000/10000 ft altitude; 5 Alford loop antennas (LP-24, DF Loop for RC-107 & RC-109 U/W MC-528 & MP-79-A) in same horizontal plane; replaces SCR-241;  installed in a K-53 truck.
  • AN/CRN-3 (same, but without truck = fixed), transportable, radio equipment in a tent.
  • AN/CRN-10 (same, with radio equipment on small "V6" (?) trailer and antenna array on simple support structure.#
  • Vs. version with 5/6/7 antennas; with/without anti back-course reflector MC-528, antenna reflector (comprising 2 reflector screens: Z-2004, Z-2005), [optional] part of antenna equipment RC-109 (Loop LP-24-A, Mast MA-5-A, mounting base MP-79-A, various cables)).
  • Aircraft receiver: RC-103. Cross-pointer indicator: I-101.
  • Note: modern day Localizer antenna systems may comprise as much as 32 antennes (typ. 7-element Yagi antennas), spanning 48 m.
  • Glide path:
  • AN/MRN-2: "portable" UHF (5 MHz segment within the 100-156 MHz range), 2-course aural Radio Range NOT GS!!! (100 W carrier + 50 W side-band; 25 W "cone-of-silence" fill-in), with station ID and periodic quadrant ID, simultaneous phone transmission.
  • AN/CRN-2: Glide Path transmitter, double beam MCW. UHF (335 MHz, 25 W CW). Preceeded SCR-592 in Feb 1944.
  • Aircraft receiver set: AN/ARN-5. Similar to AN/CRN-5 set.
  • Marker beacons and Compass Locator Marker
  • AN/MRN-3: mobile (jeep mounted transmitter RC-115 / BC-902-B) marker beacon with 1 horizontal dipole, vertical fan-shaped pattern. VHF (75 MHz, 1 W, CW/MCW); replaces BC-302.
  • Three sets: Outer/Middle/Inner marker, located inside airfield boundary / ca. 1 mile & 4.5 miles from RWY approach end, respectively.
  • Aircraft radio equipment: RC-39, RC-43, RC-193, RC193Z, AN/ARN-8, AN/ARN-12. TBC.
  • Compass Locator: ?
  • Local ground comm.
  • SCR-610, 20 W, FM, 27-38.9 MHz (2 xtal-controlled channels out of 120 possible Xtals), battery powered, range 5 miles.

AN = Joint Army-Navy nomenclature system (a.k.a. JETDS), MRN = Mobile (Ground) Radio Navigational aid, CRN = Air transportable Radio Navigational aid.

Aircraft equipment: RC-103 ILS receiver set (BC-733 receiver + I-101 indicator + control box + antenna + dynamotor); RC-39 (incl. 12 volt BC-341 marker beacon RX, 67-80 MHz), RC-43 (incl. 24 volt BC-357 marker beacon RX), RC-193 (same, post-WW2 designator). TBD/TBC.

AN/CRN-10 is also mobile LOC installation (ref. 230U2); AN/MRN-1 cabin + antenna system could also be dismounted from the truck.


Fig. XX: AN/MRN-1 - truck version with antennas in operational position; MC-528 reflector is used to suppress LOC back-course

(source: adapted from ref. 230U2)


Fig. XX: Alford loop antenna of the AN/MRN-1 and radiation pattern of the RC-109 5-loop localizer antenna array

(source: adapted from ref. 235W1; note the very narrow overlap of the yellow & blue beams)


Fig. XX: AN/CRN-10 - frame-mounted version with V-shaped folded dipoles instead of Alford loop antennas

(source: adapted from ref. 230U2)


Fig. XX: AN/CRN-2 - air transportable Glide Path transmitter for operation from trailer, with 30 ft antenna mast

(source: adapted from ref. 230U2, 235W1, 235W3)


Fig. XX: AN/CRN-2 -

(source: adapted from ref. 230Y6 and 235W1)


Fig. XX: AN/CRN-2 - vertical radiation pattern of the upper & lower antenna system

(source: adapted from ref. XXXXXXXXXXXXXX)


Fig. XX: AN/MRN-3 - marker beacon set, for operation from "jeep" truck

(source: adapted from ref. 230U2, TM11-997, and TM11-277)

Of course, by the late 1920s, flying "in the soup", as it is sometimes called, was nothing new or extraordinary. Even "blind" landings under so-called "zero-zero" conditions were successfully made, years before the advent of radio landing beacons and somewhat accurate altimeters! Here, "zero-zero" refers to zero vertical visibility and zero horizontal visibility (e.g., Runway Visual Range, RVR) outside the cockpit. For instance, one recorded true zero-zero landing took place at Croydon Airport near London in 1925, the scheduled destination of a regular passenger flight of Imperial Airways, with captain G.P. Olley at a the helm. Ref. 235B3. Regarding "blind" flights using radio navigation aids from take-off to landing, there are three notable "first" events. Regrettably, most publications only credit the first one, even though the third one is the most impressive:

  • On 24 September 1929, Lt. James "Jimmy" Doolittle of the U.S. Army Air Corps, performed a series of flights and landings, including several in heavy fog. He was piloting from the rear cockpit of a Consolidated Aircraft Corp. model  NY-2 "Husky" trainer biplane, with safety pilot Benjamin S. Kelsey in the front cockpit. Doolittle's cockpit was completely covered with a hood that completely blocked his view outside the cockpit. The cockpit of the safety pilot had no such vision restrictions. They used a large grassy air field (Mitchel Field) with an obstacle-free approach path. Doolittle used then-standard cockpit instruments and several additional, newer ones, including an artificial horizon indicator, a directional gyroscope, and an altimeter that could be corrected for changes in barometric pressure, based on two-way radio communication with the ground. They used radio navigation aids developed by the National Bureau of Standards: a Radio Range and a Marker Beacon. One of the conclusions was the lack of stable, sufficiently accurate indication of true height above terrain. Doolittle made the first “blind” takeoff, a 15-minute local flight, and landing — all by reference to instruments alone, but with a safety pilot. Ref. 235H3, 235N, 235U3.
  • Flying "under the hood" originated in France, where Lucien Rougerie introduced the foldable cloth dome at the first school for flying without visibility ("École de pilotage sans visibilité", PSV), part of the flying school that Henri Farman established in 1911 at the Toussus-le-Noble aerodrome, some 20 km southwest of the center of Paris. Rougerie also developed a simplistic fixed-base (i.e., non-motion) instrument flight simulator: a "ground training bench for pilotage without external visibility" (French 1928 patent 655874, US 1929 patent 1797794). Hans A. Roeder patented a full dynamic-response training simulator for aircraft (both airplanes and airships) and submarines in 1929 (German patent 568731). During the late 1920s, Edwin A. Link also developed a flight trainer, which he patented in 1930 as a "combination training device for student aviators and entertainment apparatus” (US patent 1825462). He upgraded his initial commercial model in 1933 for practicing "blind" flying, and expanded its features in the 1936 model C-3 with a dynamically responding altimeter and compass, and a ground-track plotter. Ref. 235P20, 229W6. Link's trainers are commonly known as Link Pilot Maker, Link Trainer, Pilot Trainer, and "the blue box" - for their standard paint scheme. A large variety of "synthetic training devices" evolved rapidly during WW2.
  • On 5 September 1931, Marshall S. Boggs, a U.S. Department of Commerce pilot, made the first “completely blind” landing in the history of aviation using only radio signals for guidance. He too flew with a safety pilot: James L. Kinney. This historic flight took place at College Park, Maryland, using a narrow hard-surface runway (100x2000 ft, ≈30x600 m), with a small obstacle below the approach path, and a VHF (90.8 MHz) landing beam. Ref. 235N, 235Y1.
  • On 9 May 1932, Albert Francis Hegenberger of the US Army Air Corps is credited with the first complete solo blind flight, from take-off to landing, i.e., without a safety pilot. He used a runway localizer course beacon and a marker beacon at McCook/Wright Field. He received the 1934 Collier Trophy for his achievement. Ref. 235H1, 235H2.

flight training simulators

Fig. XX - left-to-right: Rougerie's 1928 trainer, a WW2 RAF Link Trainer poster, and my own 1971 "flight" in a Link Trainer

(1971 photo taken at Nationaal Luchtvaart Museum "Aviodome", then still at Amsterdam Schiphol Airport; note my very special aviator sandals!)



What is? Pilot-cable, leader-cable, guide-cable: wireless but not radio. But: radio frequency EM fields: > 20 kHz i.e., > audio. Inductive: based on inductive coupling (air/water transformer).

aircraft (both airplane and airship), ships and boats. navigation. Application to aircraft landing systems dates back to ca. 1918, localizer.

fleader cable system



Tested by British government at Farnborough (cable loop around the airfield), by French government at Chartres (straight cable).

Ref. 266Z suggests that Algernon Hamo Binyon (UK) invented in 1912. However, patents naming Mr. Binyon do not cover leader cables...

Meißner 1919 German patent 423014 about inductive leader-cable systems for ship navigation.

Leader cable systems appear to have been made obsolete by the refinement of radio direction finding and the placement of radio beacons.

REF 266B, 1922:
3 ortogonal loop antennas [individually selectable or pairwise combined] installed at the tail of an airplane, 600 Hz A/C current through cable [in/on ground] that is grounded at one end [--> return current via earth/ground]. Biggest problem was radio interference caused by the engine spark plugs. With an experimental cable of 9500 ft length (+/- 3 km) "contact" with the cable could be established up to 10 thousand feet altitude (abt 3 km) and at 1 mile lateral distance when flying at 6500 ft (+/- 2 km). Current / power unknown.
Experiments with shipping system at Portsmouth (UK?) and NY.

Ref 266C, 1922: experimented with during WW1 "in some Allied ports for directing shuips during foggy weather". Adapted to aircraft by Arthur William Loth, engineer officer in the French navy, who had previously perfected the ship guiding device for use in the French navy.

229D15, p. 148. Induction signalling system as an aid to landing airplanes, only effective when the airplane was in close proximity to the landing field [ = system]. Initial config: two coils, 200 ft apart. First test with an airplane on 11-Nov-1918 (WWI Armistice Day): ground coil: 6-turn horizontal loop, 500 Hz, 24 amps., A/C: 40-turns "searching" coil of thin magwire on the underside of each fabric-covered lower wing of a biplane, tuned to resonance @ 500 Hz with large capacitors. Signals received at 300 ft altitude. Landing field experiments subsequently conducted at College Park/MD field, as a cooperative project of the U.S. Post Office Dept., the Navy Dept., and the DoC's Bureau of Standards (NE of DC), with US Army Air Service as interested party: single-turn ground coils (1500x2500 ft, ≈450x750 m). Disappointing results at frequencies of 500-1000 Hz, abandoned in favor of radio frequency methods (LF and above) of locating airfields in fog or darkness.

Kolster: August 1918 - 19, 500 Hz.


Non-Luftwaffe: French & British "leader cables" ("pilot cables") systems (LF induction), on-ground / buried / on sea bed (shipping). Doomed from the beginning due to progress in radio beacons (ca 1918-1926 for shipping).

In France still hope in 1935 (266J).

1930. Leader cable system tested by Army Air Corps at Wright Field, and was found to have "possibilities".

Temporarily (late 1950s / early 60s) revived in Britain by the RAF Blind Landing Experimental Unit (BLEU), to provide improved accuracy lateral guidance during landing. "The cable worked with an improved FM radio altimeter that BLEU developed, capable of resolving height differences to 2 feet at low altitude. The team safely conducted thousands of test landings using this system. BLEU realized that most airports did not have room to place one-mile cables, so they continued working on a radio-driven solution."

"leader cable " equipment which is used in the blind landing system recently developed by the Royal Aircraft Establishment. The principle of this azimuthal guidance system, based on the magnetic fields picked up from two cables laid either side of the runway, was described in our December, 1958, issue (p. 579). The a.c. signal frequencies in the two cables are 1,070 c/s and 1,750 c/s respectively. After separation by filters in the airborne receiver the two signals are applied to a cathode-follower comparator circuit. Any inequalities in amplitude, due to the aircraft being displaced from the runway centre line, cause the comparator to produce an unbalance voltage which is fed as a correcting signal to the aircraft's automatic pilot.

Ref. 235C4:
are those of the British government at Farnborough and of the French government at Chartres. The British installation employs a complete circuit around the landing field with a visual indicating device on the airplane instrument board. The French installation uses straight cables. The Loth Company of Paris, and several agencies in this country, including the United States Air Corps at Wright Field, Dayton,Ohio, and the Ford Motor Company at Detroit, Michigan, are experimenting with various arrangements employing leader cables. An obvious disadvantage ofthe leader cable method offield localizing is its great cost. This method generally involves the burying of cables outside the limits of the landing field, thereby introducing the expense of securing right-of-way, in addition to the actual cost of equipment and installation.

Modern ICAO/FAA/JAA precision ILS categories I through IV defined. Only implemented I through IIIC. Cat IV covers true zero-zero conditions. There are no airports with an on-ground navigation infrastructure that supports taxiing in zero visibility. I.e,. the landed airplane would have to remain parked on the runway (!) until ground visibility improves. So, investing in Cat IV installations makes no sense until that........... Apparently, there is not enough positive economic impact to warrant the required development and construction investments, and corresponding upgrades to aircraft navigation, display and control systems. "a suitably equipped aircraft and appropriately qualified crew are required".

History continues into the 1990! Ref. 266Y, 235T: Post WW2 (1949?): BLUE in UK. Ref 226D4: 1990, NASA, tests of an experimental magnetic leader cable system for guidance during roll-out and turn-off [i.e., safely clear the rwy, not including taxi from there to gate / parking!].

Ref. 235P40, 235P35. Also: 235P8 and 2359 (Loth, E.J. Simon, diagrams)

Entire subject: ref. 266A-266Z.

Dingley (ILS, USA, buried cable): referenced in ref. 229Q.

Revival (e.g., 1968 "MowBot"): wire-guided lawn mower "robots". Perimeter/boundary wire is also used to create “invisible fences” to keep pets within yards, and robot lawn mowers within zones. A typical robotic lawn mower (in particular earlier generation models) requires the user to set up a border wire around the lawn that defines the area to be mowed.

Washington Institute of Technology. In late 1933, financial cutbacks dictated by the Great Depression ended the government organized development. However, several former NBS employees then established the Washington Institute of Technology (WIT) to continue developing radio navigation at College Park. WIT then produced blind flying instruments for the U.S. Navy to test. On May 1, 1934, Navy Lt. Frank Akers took off from Anacostia Naval Air Station in a Berliner-Joyce OJ-2, and successfully landed at College Park using only the WIT instruments. A little over a year later, on July 30, 1935, Akers used similar equipment to land on the aircraft carrier USS Langley, while it was underway off the coast of San Diego. Despite these successful tests, the technology was not yet accurate enough for regular aircraft carrier operations. However, it was useful for Navy seaplanes.

Although the Navy didn't purchase the system, WIT officials created the Air-Track Corporation of College Park to sell the landing equipment to commercial airports. Pittsburgh, PA, officials bought and installed the system leading to the first blind landing of a passenger-carrying flight on January 28, 1938. Unfortunately, pilots never trusted the system enough to encourage airlines and airports to invest in this system.

W.I.T. officials created the Air-Track Corporation of College Park to sell the landing equipment to commercial airports. Pittsburgh, PA, officials bought and installed the system leading to the first blind landing [using only radio signals for guidance ?? In US or worldwide?] of a passenger-carrying flight on January 28, 1938. Ref. 235P2, 235P10.

"Diamond-Dunmore-originated at BoS" (p. 465 in ref. 229D23, 1933: "The coordination of the two sets of course indications into a single reading is of utmost importance to the pilot, relieving him of the need for considerablemental effort.") cross-pointer / crossed-needle / combined instrument / combined indicator: ergonomically much better than two stacked or side-by-side instruments, and standard to this day. Below: Bureau of Standards experimental combined instrument (1930) and , for LF Visual (2-tone) Course Beacon + VHF (90 MHz) visual glide path beacon. The two [colored] zones at the bottom ofthe instrument face were colored green and red, left to right, respectively. These we relater changed to yellow and blue because green and red could not [cannot] not be read under red night-time cockpit lighting. Blue/yellow (orig. red/green) as per approach chart symbology Blue/yellow: corresponds to colors of sectors used on Approach Charts and Visual Range symbology; found to be of little value.

Some ILS indicators have needles that are hinged and move like wipers, others have needles that move rectilinearly. Round instruments measures 3.25 inches diameter, 8.25 cm. Vertical/pendulum pointer corresponds to deviation wrt VAR or LOC 150 Hz/blue 90Hz yellow.

MIT Ground Controlled Aproach (GCA) - dead end?

Ref. 164B pp. 20-25: Lorenz ILS, autopilot coupled vs ca 1938 in US 1st coupled landing?

ILS instruments

Fig. XX: 1930 evolutions of Bureau of Standards separate field strenght / glide path meter and course-beam deviation indicator

(sources: ref. 235Y4, 229D23, 229V4 (also in 235C4, 229D24, 229D15, 235C4))

Combined lateral/vertical instrument: cross-pointer /crossed-pointer: early prototype: with a tiny aircraft symbol on each needle. Pilot to maneuver the aircraft so as to superimpose the two symbols at the center of the instrument. For obvious reasons, this instrument was much too difficult to interpret, and rejected by pilots.

ILS instruments

Fig. XX: Crossed-pointer instrument - Bureau of Standards early prototype with aircraft symbol on pointers

(source: adapted from ref. 235C7)

The next interation of this instrument simply used two crossing needles - without attached symbols. This became the standard, and remains unchanged to this day.

ILS instruments

Fig. XX: Crossed-pointer instruments - Bureau of Standards 1930 prototype model and inside of a mature model

(source - left & center image: adapted from ref. 229V4 (same in ref. 235C4); right image: adapted from ref. 235P25)

ILS instruments

Fig. XX: Bureau of Standard 1933 final model, WW2 US model I-101-C, Weston Electrical Instrument Corp. model 888-3Y2

(adapted from sources (left-to-right): ref. 229D23; aeronautique.com (accessed Aug.2020); eBay article 312913997455)

In the right-hand image of the figure above, both pointers are marked with a red "off" flag. Such flags drop into view to indicate that the affected pointer is not valid, due to no valid signal being received, or detected equipment failure, or equipment being in a powered down state.

The intersection of the two needles (pointers) represents the relative position of the aircraft with respect to the landing course beam and the glide path. The latter is represented by the small circle at the center of the instrument. Same instrument but reversed L/R Abv/Blo input signals or instrument installed upside-down. Purpose of instrument is to provide guidance ("fly left" "fly right" "descend" "maintain" "climb" for intercepting and tracking the lateral and vertical landing beams. Two philosophies: 1) the center of the instrument represents the crossing equisignal planes of the Runway Localizer and Glide Path beams and the intersection of the two pointers/needles indicates the relative position of the aircraft with respect to center of the ILS beams, vs. 2) the opposite, i.e., the center of the instrument represents the aircraft, and the needles the equisignal planes of the Runway Localizer and Glide Path beams. Per ref. 229R12-No.3, the BoS/CAA and the Army Air Forces used opposite sensing at least until 1940 (basically the same instruments, but wired in reverse). This was harmonized by the RTCA in favor of the AAF standard: the center of the instrument represents the aircraft. This became the world-wide ICAO standard in 1946. Clearly, arguments can be made both ways. However, the needles physically move with respect to the center of the instrument, so they move with respect to the aircraft in which the instrument is installed. Hence, it makes more sense that the center of the instrument should represent the aircraft.

Combined instrument

Fig. XX: The two oppposite interpretations of Left/Right & Above/Below of pointer deflections

Lateral: intercept and track the inbound course to the runway, i.e., localizes that course line --> Localizer (LOC). Vertical: curved Glide Path (GP), when straight path (i.e., an angled/sloped flat plane) became standard: Glide Slope (GS).

Equipment also sold by Lorenz to airlines and RAF, where it was know as Standard Approach Beam (SBA).

Between the two World Wars, a divergence evolved regarding aviation in the USA and Europe. In the USA, the postal, freight, and passenger aviation industry required a single consistent continent-wide system of official airways that were marked by radio navigation beacons. The European nations never arrived at recognizing the need for, or attempt to create, such a standardized system. The USA also generally transitioned well before Europe from aerodromes that were merely large grassy fields (hence, "air-field") with no specific takeoff and landing directions, to aerodromes with one or more hard surface runways aligned with the prevailing wind(s).


The world's first hard surface runway and taxi ways were constructed at Aulnat Field near Clermont-Ferrand in France. This airfield was created for the nearby factories of Michelin & Cie., where airplane production started in 1914/15. These days, the Michelin company is primarily known for their car tires and the associated Michelin Tire Man mascotte, named "Bibendum". The Michelin brothers (André and Édouard) started aviation activities in 1911. Throughout WW1 (1914-1918), they built over 1800 Bréguet and Bréguet-Michelin bomber airplanes. They also operated a bombing school at Aulnat, continued 1918-1921 by the US Army Air Service. Their 400x20m (≈1300x66 ft) concrete runway and concrete taxiways were constructed in 1916. Primary reasons: frequent propeller damage due to the bumpiness of the unpaved field, and airplanes sliding and getting stuck in the mud during rainy times.

Concrete runways did introduce a new problem: significant tire wear during the landing touch-down! Not necessarily bad for a tire manufacturer, though... Also, on a large grass field, airplanes could takeoff and land in any direction. The direction of a hard-surface runway is fixed, and has to be selected carefully, to be aligned with the prevailing wind. To accommodate multiple prevailing wind directions, or variable wind directions, one or two crossing runways may be required.

The first permanent hard surface runways in the USA were not built until much later: in 1928, at Newark/NJ ("black top" asphalt) and the Ford Motor Co. field at Dearborn/MI (concrete). That same year also in Germany (at Leipzig-Halle, 400m concrete) and Austria (at Salzburg, 1200 m concrete).

Cinder and gravel runways: between unpaved sod/grass and hard-surface. "A surface, intended for aircraft operations, composed of unbound or natural materials. Unpaved surfaces may include gravel, coral, sand, clay, hard packed soil mixtures, grass, turf or sod. (Note: Unpaved surfaces have also been referred to within the aviation industry as Unimproved Runways.)"

Refs. Ford: 229Z23. Refs to be added for Newark, 1928 Leipzig-Halle/Germany (400m concrete), 1916 Clermont

Runways are identifed by a 2-digit number from 01 to 36. So, there is no such thing as, e.g., a Runway 42 - unlike what some stupid movies may suggest. The number is derived by dividing the runway's bearing to Magnetic North by 10, rounded to the nearest integer value. As a runway has two ends, it actually has two runway numbers - one for each takeoff/landing direction. As runways are straight, these two directions always differ by 180°. So, a runway with a compass direction of 147° is designated Runway 15, and the opposite direction of the same runway is designated 15+18 = 33, combined Runway 15/33. If two or three runways of an airport are parallel (i.e., have the same number), the letter L, C, or R (for Left, Center, Right) is appended to the runway number. With four or five parallel runways, the number of one or two runways is incremented or decremented by one. The earth's magnetic poles move around slowly. So, depending on the latitude of the airport, a runway may have to be re-designated every couple of dozen years.

Not suitable for inherently inaccurate curved glide path descents to landing, also requiring a narrower localizer beam than standard in Europe (3° vs 6°).

  • Lorenz claimed the following system advantages for its landing beam system: simple antenna system, and a single transmitter as the course beam could also used for curved glide path to landing. "Disadvantage of a head-start"
  • However, Lorenz failed to recognize that these advantages had become moot, or even a disadvantage - in particular, the "curved glide path to landing".

Advantages initially generally quoted for the curved "constant field strength" landing path (ref. 229R2-No.4):

  • The landing path may be so directed as to clear all obstructions.
  • The landing path may be adjusted to suit different landing fields, esp. important for getting into small fields.
  • The landing path automatically levels off, facilitating a normal landing.
  • The landing glide may be begun at any desired altitude, within a rather wide range (say, 500 to 5000 ft).
  • Easy to use landing-beam indications - no tuning, no adjustment of receiver audio volume, as line of constant field intensity is followed.

However, extensive tests (ref. ????) showed straight glide path with level off close to ground was much better. E.g., ref. 235J. Curved --> steep descent at beginning, continuous adjustment of aircraft attitude and engine power setting - unacceptable, even more so upon intro of faster, aerodynamically more efficient aircraft with high wing-loading (weight divided by the surface area of its wings), and long flat float (eg ref 254, p. 11). Basically: power glide, descending at about 400 ft/min until contact with ground is made (i.e., no flare / round-out!), then cut off engine power completely.

Blind landing: OK, at that time, without accurate ILS, is was possible to do so successfully. As the pilots' saying goes, "any landing you can walk away from, is a good landing"! In a small and slow airplane, with a forgiving landing gear designed for rough, unpaved (grass), ondulating runways (e.g., Junkers Ju-52 transport airplane, with an approach speed of ≈150 km/h, ≈80kts; landing speed of a 100 km/h, ≈54 kts). This is actually akin to the procedure for landing on absolutely flat calm water, so-called glassy water, without as much as a ripple. On approach to the "landing", such flat water looks like a mirror and it is impossible for the pilot to get a sense of depth and judge height above the watery runway. Not recommended (or even allowed!) at night. I enjoyed practicing this for my pilot rating for seaplanes (both floatplanes and flying-boats)!

Die Lorenz-Funkbake, welche für die Zentralstelle für Flugsicherung in Berlin-Tempelhof Auf-stellung fand, hatte folgende Charakteristik: Die Antenne bestand aus einem Gestell von 9 Me-ter Höhe mit einem, vom Sender – 70 Watt moduliert – erregten Dipol und zwei Dipolreflektoren, in denen die Tastung durch Unterbruch mittelst Relais erfolgte (in einem ein Ruhestrom-relais, im andern ein Arbeitsstromrelais, was die reziproke Tastung ergab).

Da bis dahin sieben deutsche und ein österreichischer Flugplatz für 7,89 m eingerichtet waren, setzte die 4. Conférence européenne des experts radiotelegraphistes de l’aéronautique, welche im September 1934 in Warschau tagte, an Stelle der 50 cm-Welle für Signale von Blindlandeanlagen diejenige von 7,89 m.

In the UK, it became the "Standard Beam Approach System" (SBAS) system, where "Standard" refers to the "Standard Telephones & Cables Ltd." the British part of ITT's International Western Electric Co. that was aquired by ITT form ATT in 1925. Lorenz, with all its IP, was acquired by ITT in 1930 (see Fig. Lorenz/ITT/ATT org chart). YEAR??? Copied?? via Lorenz UK?? Former German Lorenz system used at civil airports and Royal Air Force airfields. Evolution?? Difference w.r.t. BABS - Beam Approach Beacon System, widely used approach system at Royal Air Force airfields? ref. 235P14 Pt 2 p50: SBA regularly interrupted beam keying (i.e, reflectors both deactivated, omni transmission by dipole) and 2-lettter beacon Morsee-ID was transmitted for a few seconds.

The Low-Frequency Radio Range (LFR), also known as the Four-Course Radio Range, the A-N Radio Range or the Adcock Radio Range, was developed in the late 1920. This 1937 Westinghouse transmitter is identified as "simultaneous" because, unlike earlier versions, it was capable of transmitting the range navigation signals (A and N) and voice transmissions at the same time.

Flight into "instrument meteorological conditions" by non-qualified pilots typically ends catastrophically in a matter of a few minutes.

Outer Marker Middle Marker Inner Marker

Fig. XX: Indication of passage of Outer, Middle, and Inner Marker on standard modern indicator or display

(associated audio signals: OM 400 Hz 2 dots/sec, MM 1300 Hz 2 dashes or 2 dots/sec, IM 3000 Hz 6 dots/sec)

ILS marker beacons

Simulated sound of over-flying the Outer, Middle, and Inner Marker of a modern ILS


The words "bombardment", "bomb", and "bombing" trace back to the word "bombard": a ca. 14th century type of wide-muzzled canon or mortar, for shooting large round stone projectiles at walls of enemy fortifications. The non-entertainment use of rockets dates back further: to the early 13th century, when the Chinese used “fire arrow” rockets (gunpowder-filled tubes) against Mongol invaders. The early 15th century Middle English word "canon" comes from the 8th century Mesopotamian word "gina" for "reed", via ancient Greek, Latin, and the Italian word "cannone" (reed or tube). Man-carrying kites were used extensively in 6th century China. In the 19th century, they were briefly considered for throwing projectiles, rather than the original reconnaissance purposes. Catapults, for hurling projectiles at enemies, date back to 4th century China.

Clément Ader was a French aviation pioneer. The first autonomous takeoff in a motorized "heavier than air" aircraft is attributed to him. In October of 1890, he used the "Éole" ("Wind"), his bat-like airplane powered by a steam engine, for a brief bouncy "flight" (if you can call it that): multiple hops, 20 cm above ground, over a distance of 50 m. In 1892, some 20 years after the Franco-Prussian War, the French "Ministère de la Guerre" (War Ministry) signed a contract with Ader, for developing "a machine capable of bombing the German enemy". The aircraft had to fully dirigible, be able to carry a pilot and a passenger or explosives, and fly for six hours at a speed of 55 km/h (≈ 30 kts) at an altitude of several 100 meters. Ref. 280D1.

Bombing history

Fig. XX: Clément Ader’s "Éole" monoplane - 1890

(source: adapted from "Clément Ader, 9 octobre 1890", 15 min video documentary, Albert Bayard, Bibliothèque de France, accessed January 2022)

So, the active pursuit of "aerial bombing" capability goes back at least that far. It refers to manually or mechanically dropping (= passively releasing or actively ejecting), a "bomb" from an aircraft, such as a balloon, a dirigible (airship), or an airplane. Note: all airplanes are aircraft, but not all aircraft are airplanes. Only airplanes, as the name suggests, have wings. A "bomb" is generally understood to be an explosive, incendiary, or otherwise pyrotechnic projectile.

Passive projectiles, in the form of relatively small steel darts of various shapes, intended to pierce helmets, skuls, and other parts of the body. During after having practiced in Morocco in 1912.

The 19th century was a very bellicose century: worldwide about 600 wars and significant armed conflicts. Source: wikipedia.org. That is more than three times the number for the 18th century! At the turn of the 20th century, this horrible record led to the first international treaties that addressed the conduct of warfare. They were negotiated at the 1899 and 1907 Peace Conferences, held at The Hague in The Netherlands. Many of the important States, however, such as France, Germany, Italy, Japan and Russia, did not sign or ratify the final Declaration and all of its Articles. Austria-Hungary signed, but did not ratify it. Of the great Powers, only Great Britain and the United States ratified it. The 1899 Peace Conference predates the advent of powered airplanes. However, a Conference "discussion of the question of throwing projectiles from balloons" already foresees "... the use of more perfect balloons may soon become a practical and lawful means of waging war". This led to the following Declaration (ref. 280D2):

"The contracting Powers agree to prohibit for a term of five years, the discharge of projectiles and explosives from balloons or by other new methods of a similar nature".

I.e., no bombing from any type of aircraft. The Declaration had the following limitation:

"The present declaration is only binding on the contracting Powers in case of war between two or more of them. It shall cease to be binding from the time when, in a war between contracting Powers, one of the belligerents is joined by a non-contracting Power".

The above declaration had already expired several years before it was extensively discussed during the second Peace Conference, in 1907. It was neither renewed nor made permanent. However, a permanent Declaration of the 1899 Conference already covered aspects of “bombardments”, including (Article 25):

"It is forbidden to attack or bombard towns, villages, dwellings or buildings that are not defended."

This was considered by some Conference parties to already adequately cover aerial bombardments (i.e., not only conventional bombardments by surface-based and naval guns and canons), as such bombardments were not explicitly excluded from that general 1899 Article.

The first recorded experiments with dropping bombs from an airplane took place in California in 1910 and 1911 – not as part of armed conflicts. Lieutenant Paul W. Beck, in a Farman III biplane flown by the French aviator Louis Paulhan, conducted a rudimentary dummy-bomb dropping demonstration during the January 1910 Los Angeles Air Meet at Dominguez Field. A year later, at the 1911 Air Meet at the Tarforan Racetrack near San Francisco, Lieutenant Myron S. Crissey (U.S. Army Air Corps), dropped the first “live” ( = explosive) bombs - of his own design, with stabilizing fins - from a Wright airplane. The plane was piloted by Phillip Parmalee, member of the Wright Bros. Exhibition Team.

Bombing history

Fig. XX: Lt. Crissey holding a dummy bomb, ready to go aloft in a Wright plane at the 1911 Air Meet near San Francisco/California, with pilot Phillip Parmalee

(source: US Air Force Historical Research Agency)

In August of 1911, the Michelin brothers (André and Édouard), sponsored an aerial bomb-aiming competition, the "Aéro-Cible Michelin” ["Aero Target Michelin"]. They considered the competition indispensable for improving national defense. The monetary prizes were equivalent to appr. 80 and 160 thousand euros in Jan-2022 (≈90 & 180 thousand US$). By the way: in 1916, they built the world's first hard-surface runway & taxiway at their airplane factory's Aulnat aerodrome. In December of 1911, André Michelin proclaimed the need for a French air force with 5000 airplanes, and the same number of pilots - France being the only country to be able to do so, because, well,... the French are "special" in that only they have the required "brightness of mind and precision of gestures" (ref. 280D5). A persistent misconception, despite France indeed being the world leader in aviation at that time...

Bombing history

Fig. XX: 1912 promotional postcards of the Michelin company (artwork by Georges Hautot)

(source: unknown; Bibendum (the “Michelin Tire Man” mascot) refers to the bombs as “Bibendum turds”)

The actual Michelin competition took place in 1912 at the artillery field of the military Camp de Châlons (a.k.a. Camp de Mourmelon-le-Grand), ca. 160 km (≈100 miles) northeast of down-town Paris. It was spread out over five rounds, from February through August. Ref. 280A1-280A12. There were five competing teams - one civil and four military. They had to use 7.1 kg (≈16 lbs) round dummy projectiles with a 16 cm diameter (≈6.3 inch). During the initial rounds, the ground target was round with a diameter of 20 m (≈66 ft). A minimum altitude of 200 m (≈650 ft) had to be maintained. During several rounds, one of the bomb aimers/releasers was the American USN Lieutenant Riley E. Scott, with his patented bomb-release device (see ref. 280A3, 280A8, and his 1910 US Patent 991378 "Means for dropping projectiles from aerial crafts"). The final rounds of the competition used a 120x40 m target (≈400x130 ft - the size of an airship hangar) and a minimum altitude of 800 m (≈2600 ft). Despite the pilots and airplanes being French, the results of the first round were "negative" and "not exactly brilliant" (ref. 280A2, 280A4): 15 bombs per airplane, but the target was not hit.

Bombing history

Fig. XX: A competition dummy bomb suspended from Lt. Mailfert's airplane (left) and a Riley Scott bomb release device

(source: ref. 280A6 (left) and 280A3)

Also in August of 1912, there was a competition in Gotha/Germany that included bombing trials: the "Aeroplane Turnier" ["Airplane tournament"]. It was organized by the Deutscher Fliegerbund - the German association of flying clubs - and the Reichsflugverein. Only military participants were allowed. They used the same type of dummy bombs as the Michelin competition, ground targets of 100x100 m (≈330x330 ft), 150x150, and 200x200 m - with minimum altitudes of 200, 400, and 800 m, respectively. A moving target was also used: a tethered balloon (30 m long, 3 m diameter, 4 m above ground) from a minimum altitude of 50 m. Ref. 280A13. Also see ref. 280D3, 280D6. The British War Office did announce its first Military Aeroplane Trials in 1911, which were held early August of 1912, at Larkhill on Salisbury Plain. However, it was focused entirely on aircraft performance under various conditions, construction, engine technology, etc. No bombing trials were held. The August-September 1912 military competitions at St. Petersburg/Russia did include dropping of bombs. Actually, throughout 1912, and probably as early as 1910, dropping dummy bombs was a popular event during many public exhibition flying events and aviation meetings in Europe and the USA. In all fairness, mediocre results at bombing trials were often caused by lack of training and proficiency, the pilot also having to simultaneusly act as bomb aimer/releaser, etc. (ref. 280D10, and other factors listed below).

During 1996-2000 I was member of a large flying club at Seattle Boeing/King County Field. This is where I got my Instrument Rating in 1998. One of the highlights in the flying club was the annual fly-in at Copalis Beach State Airport on the Pacific coast, 95 miles (150 km) southwest of Seattle/WA. It is the only beach "airport" in the USA. As the name suggests, the "runway" is the sand of the narrow beach. Landings and take-offs have to be timed well with the tides. Use standard soft-field landing & take-off techniques and always keep the carburator heat on! The damp medium-dark sand at low tide is surprisingly hard. You do not want to get into the soft dry sand! I have made several landings on this beach (and the same number of take-offs) in a Cessna 172 (4-seater) and a 152 (2-seater) airplane. During the August 1997 fly-in, I participated in a friendly bombing competition with flour-filled paper bags. I piloted a Cessna 172, with my friend and colleague R. Büse as bomb aimer/releaser. Flying low-and-slow, we hit the small target beautifully... but got disqualified for flying well below 50 ft during our bombing run. It was great fun nonetheless!

Copalis Beach runway

Fig. XX: August 1997 - myself on the runway of Copalis Beach

The world’s first bombing attack took place during the Italo-Turkish War. This war was fought from September 1911 to October 1912 in Ottoman Libya by the Kingdom of Italy and forces loyal to the Ottoman Empire. On 1 November of 1911, Lieutenant Giulio Gavotti of the Royal Italian Army Air Service, took off in an early-version “Taube” (EN: “Dove”) monoplane and dropped four bombs over Turkish-Arab encampments at Ain Zara and Tagiura, two oases on the outskirts of modern-day Tripoli. Contrary to a rather euphoric Italian newspaper article the next day (ref. 280D4, with translation), little damage was done, and there were no casualties.

Bombing history

Fig. XX: A 1913/14 model “Taube”, built by the Rumpler factory under license from the Austrian designer Ignaz "Igo" Etrich

(source: adapted from German Bundesarchiv image nr. 146-1972-003-64)

Those bombs were actually hand grenades, originally developed by Giuseppe Cipelli at a factory in La Spezia/Italy in 1907/08. They were filled with picric acid - which is in the same chemical family as trinitrotoluene (TNT, "dynamite") - and weighed about 1½ kg (≈ 3 lbs) each. Cipelli was killed in 1908, by the accidental explosion of one of his creations. On 6 March of 1912, the Italians dropped the first bombs from airships: on a Turkish-Arab camp at Zanzur, west of Tripoli, from an altitude of 6000 ft. Ref. 280D7, 280D9. Those were heavier than the Cipelle grenades (ref. 280D8).

Bombing history

Fig. XX: A Cipelli hand grenade – used as a bomb by Gavotti in 1911

(source: adapted from "L'aeronautica", T. Brinati, U. Fischetti, S. Stefanutti, Vol. II of "L'uomo e l'aria", Dr. Francesco Vallardi (publ.), 1939, 623 pp.)

About half way through World War I, using airships for bombing of land targets had become obsolete and came to an end. They had become an easy prey for increasing anti-aircraft defenses on ground, as well as fighter aircraft. They were also rather ineffective, as far as damage inflicted and casualties caused. So, they were replaced with much smaller fighter and bomber airplanes. Those were a lot less expensive to build and maintain, required a much smaller crew and ground support, and could fly increasingly faster and higher (during 1910-1912, the world airplane altitude record increased from ca. 300 to over 3000 m (≈1000-10000 ft). However, due to their flight range and endurance, airships were retained in service somewhat longer, for naval reconnaissance and bombing of ships.

Bombing history

Fig. XX: An RNAS lieutenant about to drop a bomb from the rear cockpit of the gondola of a Sea Scout Zero airship, ca. 1916

(source: Imperial War Museums (IWM) Photograph Archive Collection, catalog nr. Q 67698; used in accordance with IWM Non Commercial Licence)

Bombing history

Fig. XX: The tandem-cockpit control car (gondola) of Sea Scout Zero airship SSZ 8 - with a bomb rack behind the rear cockpit

(Royal Navy SSZ: length 143.5 ft (≈44 m), diameter 27.9 ft (≈8.5 m), height 43.9 ft (≈13.4 m), speed 50 mph (≈80 km/h), engine: 1 x 75 hp)

"Bombing brought to being a number of crude devices in the first year of the War. Allied pilots of the very early days carried up bombs packed in a small box and threw them over by hand, while, a little later, the bombs were strung like apples on wings and undercarriage, so that the pilot who did not get rid of his load before landing risked an explosion. Then came a properly designed carrying apparatus, crude but fairly efficient, and with 1916 development had proceeded as far as the proper bomb-racks with releasing gear. Ref. 280D11"

Bomb racks. Pix.

Actual bombing. AGARD Ref. 280C3. C1-C4.

Factors affecting the trajectory of a released bomb (ref. ?????):

  • Motion of the aircraft at the time of bomb release. Up to the moment of release, the bomb follows all movements of the airplane. These movements continue after the release.
  • Even a modern-day automatic pilot cannot keep an airplane at a perfectly constant altitude, constant speed, and without any pitch, roll, and yaw motion ( = rotation about the three aircraft axes of motion). 
  • Variation in wind velocity and direction vs. altitude.
  • Separation effects: tumbling, precession, wobbling. These movements significantly impact the aerodynamic behavior of the bomb. Bombs are typically designed so as to minimize these movements and expedite their xxxxxxx.
  • Coriolis effect: rotation of the earth moves the the target relative to the falling bomb.
  • The significance of the effect depends on the fall time of the bomb.
  • Manufacturing tolerances of the bomb. This impacts weight, center of gravity, and aerodynamic behavior (drag, etc.)..
  • Non-standard atmosphere (temperature, absolute pressure, density, dynamic viscosity).
  • Location and altitude dependent earth's gravity acceleration "g".
  • The earth is neither a smooth sphere, nor homogeneous. At Sea Level, gravity at the earth's poles is about 0.5% larger than at the equator. Gravity at, e.g., 20 thousand feet (6 km) Above Sea Level is about 1% smaller than at Sea Level.

bomb trajectory

Fig. XX: Simplified trajectory of a released bomb

(3D graph neglects separation effects, Coriolis effect, wind direction vs. altitude, gravity variation vs. altitude, etc; 2D graph: adapted from ref. 280B2)

Also diagrams in ref. 230R5, 280A7 & 280A3 (1912).

Ground-mapping radar systems Such radars (e.g., H2S in WW2 tbc) show radiowave returns ("echoes") from terrain (land, transitions between land and large water such as rivers & coastlines) and objects on land (e.g., cities) on a display. The displayed contours can be used for navigation as well as identification / location of bombing targets.In all other uses of radar (e.g., intercept radar, weather radar), such returns are actually highly undesirable and, therefore, referred to as "ground clutter" or simply "clutter". Suppressing clutter is not an easy task, and in airborne WXR not really possible without using a 3D terrain database and accurate 3D position data at all times, to correlate terrain data and radar returns. This was first done on the Airbus A380 by the Honeywell AESS system. I had the pleasure of being systems engineer on its development program 1996-2007.


First, we have to get some terminology straight, as there is some general and persistent confusion, particularly in non-German publications (except 230R3):

  • "X-Verfahren" / X-Procedure (process, method, system)
  • "X-Bake" / X-Beacon , X-Station (transmitter station; German code name "Wotan I" (but not for original version?), Brit. code name "Ruffian")
  • "X-Gerät" / X-Equipment (apparatus): equipment set in the aircraft: "X-Empfänger" (TFK (dev) /Siemens (prod) FuG 22 Leitstrahl Doppelempfänger. "Anna" ), = EBL2 with additional amplifier/differentiator stage for the AFN2 ?

Its purpose: "Bombenabwurfverfahren", "Bomben-Ziel-Abwurf-Verfahren", "gezielter Blind-Bomben-Wurf" says it all (ref 183, 230R5). Precision BLIND bombing. The purpose is to drop bombs on a predermined target, without being able to visually identify it and aim at it. The process to do so accurately, is easiest to understand when going through it "right-to-left" instead of the standard "left-to-right". I.e., begin at the impact of the dropped bomb on the target, and back up from there to the bomb release time / position, and how to navigate to that position - not from take-off or approach of the target, determining the bomb release time and position..

The "Lorenz Beam" was designed for flying a specific course-line towards a short-range beacon that had relatively wide beam-aperture (5º). In 1932, Dr. Johannes (Hans) Plendl of the Deutsche Versuchsanstalt für Luftfahrt (DVL, German Aviation Test Establishment) already identified the need for a directional beam system, to guide bombers to a target along a course-line away from the beacon, at night and in poor weather (visibility) conditions. Plendl was the national commissary for RF research ("Bevollmächtigte für Hochfrequenzforschung") from November 1942 until December 1943, and also headed up the national agency for RF research "Reichsstelle für Hochfrequenzforschung" (RHF) that was established mid-1943.

Make distinction between "pre-Knickebein" and "Post-Knickebein". Ref. 2C.

Proof-of-concept was done with "Lorenz Beam" systems. However, these commercial systems had neither the required range, nor the required accurate and narrow equi-beam (±0.1º aperture). Therefore, the operating frequency was increased from 30-36.2 MHz (wavelength λ ≈ 9 m ± 9%) to the 66-77 MHz range (wavelength λ ≈ 4 m ± 8%), and the beacon was equipped with more powerful transmitters. The German code name for the "X"-station ("X-Station", "X-Bodenstelle", "X-Peiler", "X-Bake") was "Wotan I". The basic antenna system comprised two vertical dipoles. The antenna system as such was rotable to the desired [primary] beam direction, but not (continuously) rotating. One dipole was energized continuously with an AM carrier that was modulated with a 2000 Hz tone. The second dipole was placed at a distance of 3½ λ, and was energized via a motorized capacitive phase-shifter. The phase was changed stepwise, every 0.5 sec [??how many steps in 360? rpm?]. The resulting radiation pattern had 14 or 18 E/T-beams of about equal strength [lobe size, see Fig. 84], and an equi-signal zone with a width of less than ±0.1º. The large number of major lobes was very awkward: the aircraft had to fly across the lobes, and count the passages of the "T" (dash) zones to find the intended guide beam ("Marschleitstrahl", the 7th of 14 (as in Figure 84 below), or the 9th of 18 in the larger system).

Ref. 185H: in 1933 Hans Plendel (DVL) proposed a VHF precision nav system for bombing without visual contact with the target; development contract for this "X-System" (a.k.a. "Wotan 1") was awarded to him in 1934. "The “X-System” worked on the principal that a guiding beam was directed over the target and served as a course beam. Two other beams on different frequencies intersected the course beam at right angles prior to the target. The [crossing] beams allowed the pilot to determine his speed over the ground with a special "X-Clock" to determine the correct release time for his bombs." After extensive testing (@ Köthen), the "Wotan I" VHF navigation system (66-77 MHz) was operational in 1937. 14-beam antenna system: 2 vertical arrays, 1 transmitted a continuous signal, 1 an intermittent 120 Hz signal (?); 2000 Hz E/T tone pulse modulation, +/- 0.5° equisignal beam width. A.k.a. "multi-beam Rechlin system". A larger 18-beam system was subsequently developed, with "2 reflectors". Eight built throughout Germany in 1938, late 1939 most moved to the western front, later to the French channel coast. X-receiver: Siemens FuG22 "Anna", bascially an E Bl 2 with additional amplifier/pulse-differentiator stage. AFN2 indicator used [per 230R3 not initially], but connected such that 1 needle showed LOC guide beam, the other the transverse/crossing beam [????]. The system was used as follows: The frequency of the UHF-beam (A) was tuned into the first receiver which was tracked by the pilot. See the figure on the next page. The flight engineer manned the second receiver and it was his job to determine the time that the aircraft crossed the transverse beam signals (B) and (C) which transmitted at different frequencies. Usually these beams were detected 18 and 6 km before the target and used to determine the ground speed of the aircraft. A “X-Clock” (fabricated by Hartmann & Braun, later by Baeurle& Sons) was used to calculate the time to the target. Wind drift, altitude, aircraft speed was measured and accounted for. The clock would then show the time for the aircraft to drop its bomb. X system used September 1939 during invasion of Poland, and from France August-1940 to June-1941 in bombing raids at targets in England.

X System

Fig. 7X: Pre-WW2 X-system development test sites

(source: adapted from Fig. 7, map/Karte 1 and Fig. 8, map/Karte 2 in ref. 230R5)

X System

Fig. 7X: X-System stations used during the September 1939 invasion of Poland

(source: adapted from Fig. 9, map/Karte 3 in ref. 230R5)

Ref. 6D, §29: The first operations of the war with mobile X-Stations were on two bombing missions against a munitions factory in Poland. §39: Kampfgruppe 100 later flew in Russia with mobile "X" stations, which were set up with great speed.

X System

Fig. 7X: 1940 X-System ground stations for targets in England

(source: adapted from map Fig. 10 and text on pp. 49/50 in ref. 230R5)

Ref. 6D: After several years Plendl completed his apparatus, and experiments were conducted on the X-System by Versuchs Regiment Köthen (Ln Abt. 100. Luftwaffe Signal Corps Detachment 100) with the bomber Gruppe that later [FD: late 1941] became K.G. 100 [FD: 1. Kampfgruppe 100, 1.K.Gr.100; Köthen, ca. 135 km / 84 miles southwest of downtown Berlin: small civil airfield since 1928, airfield + industrial site acquired by Luftwaffe mid-1936, 360 hectares (≈900 acres) total, Nov 1937 home of the Luftnachrichten Lehr- und Versuchsregiment, source: ref. 230R2, 230R3). Antenna system: 2 vertical arrays (vs single antenna), one transmitting omni-directional signal (2000 Hz tone modulation), the other transmitted 120 pulses per minute = intermittent (on/off). E/T rythm. Radiation pattern: 14 beams (in order to obtain high beam "resolution") with ~0.05° ???? width. Later an 18-beam version was developed. Large number of beams not user-friendly whatsoever, as hard to identify which beam to use (or for enemy: determine which "target" beam was in use). Range later increased by adding reflector behind each antenna. Crossing beams 18 and 6 km before the target.

Q: difference between transportable, mobile, and fixed-base antenna systems?

Fixed-base Wotan I station locations?

3-beam system: Marschleitstrahl + Vorsignal (Querleitstrahl) + Hauptsignal (Querleitstrahl 5 Km vor Ziel); vs 1+3= 4 beams or more?

FD: The need for (near) right angles is illustrated in Fig. XX [TFK Kompaß section]; this also applies to all other crosssing-beam systems, such as "Knickebein".

Ref. 183. Plendl's concept used two directional beacons, sufficiently spaced apart. The centerline of their beams crossed each other at the target. Plotted on a chart, the two beam lines form a big "X". Hence, this concept was referred to as the "X-Method" ("X-Verfahren", "Bomben-Ziel-Abwurf-Verfahren", "gezielter Blind-Bomben-Wurf" - like the Y-Verfahren). The aircraft would intercept and track the E/T equi-signal of a director-beam ("Marschleitstrahl") to the target. A second beacon would transmit (at least) three E/T beams that would cross the director-beam at certain distances just before reaching the target. Upon reaching the first cross-beam, the aircraft had to well established on the equi-signal course-line. Reaching the centerline of the second and third cross-beam was used to determine when to release the bombs. This was done with a special stopwatch, the "X-Clock" ("X-Uhr"), see Figure 45B. This mechanical calculator computed the "bomb release" time, based on actual groundspeed towards the target (derived from the times between the cross-beams), release altitude, and type of bomb. In a simplified version, only a single cross-beam was used.

Ref. 185C.

ref. 230R5: A/N not E/T?

The (lead) aircraft required an "X-Gerät" ("X-Equipment") installation. This comprised (see p. 106 in ref. 2A, 229R, 230R3):

  • Two dedicated "X-receivers", FuG 22 "Anna" receivers for 66-77 MHz (20x RV12P2000 tube/valve), each with a ¼λ vertical rod (dipole?) antenna; vs. FuG-17-X receivers?
  • Two AFN2 ("Anzeigegerät Flug-Navigation") course-deviation indicators (right-hand instrument in Figure 82A).
  • The vertical down-pointing needle indicates left/right deviation from the course line. The needle pulses to the left or right, in the rythm of the dominating "E" or "T" signals ("Zuckanzeige", "kicking meter"). When receiving the beacon and the position is "on course", the needle is centered.
  • The horizontal needle (pointing at the vertical scale on the left) is a signal-strength indicator, and acts as a simplistic near / far indication of distance to the beacon.
  • The indicator lamp in the center is illuminated when receiving a marker beacon during approach to landing. It is a line-replacable neon lamp. On the AFN1, it is located at the top.
  • Two AVP units ("Anzeigeverstärker Plendl", "Plendl-method Indicator Amplifier"), one for each receiver/AFN2 pair.
  • A power converter unit for the required anode & grid DC-voltages, and a power-distribution unit,
  • A "Prüfuhr" (a.k.a. "X-Uhr"): "Bombenabwurfautomat" (automatic bomb-release timer/computer; multi-stopwatch bomb-release timer (see Figure 83 below).

Dual RX/AVP/AFN, to be able to simultaneous monitor the main guide beams and the crossing beam.


Fig. 82A: Anzeigegerät für Funk-Navigation (Radio-Navigation Indicator) - model AFN1 and AFN2

(vertical needle/pointer indicates Left/Right course deviation, horizontal needle shows signal strength = appr. distance, "nahe" = "near")

Note that these two instruments do not have the same size. The AFN1 is a somewhat larger: its bezel has an outer diameter of 83 mm (≈3.3 in), whereas the cylindrical housing has a diameter of 79.4 mm (≈3.1 in) and a length of 72 mm (excl. protruding connectors; ≈2.8 in). For the AFN2, these dimensions are 66.7 (≈2.6 in), 57 mm (≈1.3 in), and 57 mm, respectively. See these diagrams.

AFN1 and AFN2: at least as early as 1939. AFN2 desigend and manufactured by Siemens SAM (LGW-Hakenfelde/Berlin). AFN2 was also used during aproach to landing flight-phase, and for D/F purposes with sets such as "Bordfunkgerät FuG 16: Empfänger E16Z + Zielflugvorsatzgerät ZVG 16" (ZVG 15/16/17 had the Dieckmann-Hell RDF converter,covered by their 1927 German Reichs patents 481703/482281, ref. 230Z), "Zielfluggerät Peil G IV" (1941), "Funk-Peil-Gerät FuG141" (receiver E141) and "Bordpeilgerät Peil G 6", though no use for the neon lamp.

AFN1 and AFN2 are the Luftwaffe version of the Lorenz "1936 beam approach indicator" instruments, see Fig. xx. The AFN2 has a 40 μA moving-coil microammeter for the left/right course deviation needle, and an 80 μA meter for the signal strength needle.

Converter circuitry (eg AVP) was integrated into the EBl 2 receiver.

X-Uhr, X-clock

Figure 83A: X-Uhr automatic bomb-release timer/computer - model Pr.U.1

(source: ref. 230A but with its explanatory legends corrected. Also see ref. 2A1, and pp. 106/107 in ref. 2C2)

In the photo above, the pointers are at the position that would be typical for the moment approaching bomb release: the red pointer is about to overlap the black pointer, and the black pointer is set back from the green pointer.

X-Uhr, X-clock

Figure 83B: Front and top view of X-Uhr model Pr.U.28

(source left image: ”Pr.U 28, 1939” page of deutscheluftwaffe.de, used with permission)

There were two manufacturers of the Prüfuhr. The Hartmann & Braun A.-G. company in Frankfurt/Main was a maker of electrical test and measurement instruments (incl. strip chart recorders, pressure gauges, temperature gauges, fuel gauges) and control equipment. They made the initial Prüf-Uhr model 1, the Pr.U.1. The Tobias Bäuerle & Söhne company was a maker of clocks and mechanical calculators in St. Georgen in the Black Forest - a traditional clock making region, and not just cuckoo clocks with intricate wood carvings. They built the smaller X-clock model Pr.U.2., as well as the later version model Pr.U.28. On the Pr.U.28, the setting knob for the black pointer is lower than on the Pr.U.2. Per ref. 2B, Hartmann & Braun received an order for 100 Pr.U.1 clocks, and Tobias Bäuerle & Söhne for 13000 (!!!) model Pr.U.2 clocks.

The equipment label in the Figure above shows that the clock was developed at "E.Re.F". This is the "Erprobungsstelle Rechlin, Abteilung Funkforschung". That is: the radio research department of the Luftwaffe test site at Rechlin, about 100 km north-northeast of downtown Berlin. This department covered "Hochfrequenzforschung und Leitstrahlverfahren": research of high frequency radio and flight guidance beams. The clock was developed there by Dr. W. Hepper.

The winding key can be removed from the winding mechanism and stuck into a small cylindrical holder to the right of it. The clock is actually wound through the back of the instrument, via external right-angle gearings to the top of the housing, see the center image in Fig. 83B above. The housing of the Pr.U.2 and Pr.U.28 clocks has a diameter of 17.5 cm (≈7 inch), and the clock weighs 3.65 kg (≈8 lbs), ref. 212B. Note that the Pr.U.28 X-Uhr in Fig. 83B has a third small scale that is marked "0 - 4 hours". It indicates to what extent the clock spring is wound. Model Pr.U.1 does not have this feature.

Ref. 185H: cross-beams crossed main around 18 and 6 km prior to reaching the target. [FD]: not fixed distances.

The X-Uhr calculations the bomb-release moment based on a fixed, standard approach altitude and the actual speed over ground. This speed is based on the distance (e.g., 10 km) between the points where the two secondary guide beams cross the main guide beam that is pointed at the target location. The time that elapses between these crossings is mechanically derived from the two moments when the operating lever of the clock is pressed. As the next Figure shows, the calculator mechanism is quite complex. It uses two variable-ratio bevel gears to calculate "time of flight" and drift of the bombs. The 2-prong electrical connector is connected to a switch contact for automatic bomb release.

X-Uhr, X-clock

Figure 83B: Inside of a Pr.U.28 X-clock (made by the Tobias Bäuerle & Söhne company) and its dimensions

(source left image: "Ln.28901 Prüfuhr PR.U 28, 1939" page of deutscheluftwaffe.de, used with permission; right: adapted from ref. 212B)

X-clock operation: ref. 230F vs.230A/Fig.83A, vs. 230E ("The second intersecting beam was at 20 km distance, and told the navigator to start a special clock with two independent hands, one of which started rotating at this point. The third beam intersected at 5 km from the target, and was used to start the second hand on the clock. When the two hands of the clock aligned, an automated bomb release was triggered electrically"). FD: no fixed distances, as these distances from the target depended on the distance from the X-beacon to the target, the fixed angles of the X-beacon's radiation pattern, and the line from the main beam to the target. Hence the need for adjustability of the X-Clock, to account for these! Look-up tables for corrected distance-ratio, to account for retardation (D: "Rückdrift"). Also see ref. 280C.

Wotan I beacon pattern

Fig. xxA: The 6-lobe radiation pattern of a Wotan I beacon with 1.6 λ antenna spacing

(radiation pattern shown for "free space"; the NEC file of my 4NEC2 model is here)

Note: NOTE below: multiple equisignal beams, not created by two partly overlapping beams, but rapidly E/T alternating omni-directional pattern and a "fan" of beams (initially switched with vacuum switches, later motorized rotating capacitors = contact-free). A fan pattern with 14 lobes in 360° results in 2x 14 = 28 narrow equisignal beams, with 2-4°and 10-15° spacing.  Not easy to use at all, had to count E and T zone transitions, required special training. Modulation tone 2000 Hz & 120 Hz (E = ??? msec, T = ??? msec) vs 1150 Hz & 1/8 + 7/8 sec E/T keying of the 33 MHz Lorenz landing system. Typ. sub beam #7 was aimed at the target --> half of the 14 lobes never used. Adding reflectors to dipoles to concentrate more of the TX power in the forward half of the pattern, thereby increasing range. 66-77 MHz VHF (0.5 MHz channel spacing, ref. 230R3).

Add 2-image dyn gif.

Wotan I beacon pattern

Fig. 84: Polar plot of the radiation pattern of the Wotan I beacon

(source: adapted from ref. 2)

Wotan I beacon pattern

Fig. xxA: The 14-lobe radiation pattern of Wotan I beacon with 3½ λ antenna spacing

(radiation pattern shown for "free space"; the NEC file of my 4NEC2 model is here)

X-beam pattern

Fig. XX: Creation of E/T equisignal beams with 3½ λ antenna spacing

Wotan I beacon pattern

Fig. xxB: The 18-lobe radiation pattern of Wotan I beacon with 4½ λ antenna spacing

(radiation pattern shown for "free space" ; the NEC file of my 4NEC2 model is here)

E/T equisignal beams created by stepwise toggling phase shift between the two antennas in rhythm of the E/T keying. Note that when phase shift causes rotation of the radiation pattern by more than 2°, additional (and undesirable) equisignal beams emerge. This characteristic limits the achievable minimum narrowness/sharpness of the equisignal beams.

Ref. 230R3: fixed ground station/installation had "fan" pattern with 14 lobes, the mobile station had 3 lobes. Various antenna configurations: 2 vertical dipoles each with a reflector (also active dipole?), vs. 6 horizontal + 6 vertical dipoles vs. 10 dipoles. All rotable (not rotating). Dot/dash keying. Prototypes completed late 1934.

Vs: transportable station with 6+6 vertical dipoles (2 side-by-side broadside arrays) for single equisignal beam (have photo).

Vs.: single-beam fixed-base "cross-beam" station with 2 vertical dipoles, each dipoel with 2 reflectors (or reflector + director???; have photo)

The complexity of the method required extensive pilot training. Only a rather limited number of aircraft was equipped with the X-Gerät. To cope with jamming by the British, the system was modified to use additional frequency channels, and a tone modulation well above the standard audio bandwidth of regular receivers. This provided some temporary relief from the jamming. The "Battle of the Beams" between Germany and Britain took place from late-1939 through mid 1941. Ref. 6G, 28, 38A, 230C, 230D, 230E, 230F, 230G. During this period, the British developed countermeasures to German radio-navigation systems and to radio-telephony communication of fighter/bomber control systems. The Germans responded by modifying those systems and introducing new systems, to which the British developed new or adapted countermeasures, etc.

By May of 1941, the Lorenz X-System was abandoned in favor of the "Y-System", see further below. A secondary reason for abandoning the X-system was the absence of a system for formation flying "in the clouds". This limitation had been recognized, and implied that a simpler system with crossing beams would be just as effective.


The Telefunken company had already been tasked early 1939 to develop a simple beam system that was compatible with the Lorenz Funklande Empfangsanlage Fu Bl 1 ("blind approach & landing receiver system") that was standard equipment in Luftwaffe aircraft (ref. 32). The receivers had much higher sensitivity than required for operation with a landing beacon, to enable long-range navigation. This new system was also an E/T beam system, and also used two crossing marker-beam beacons. Telefunken's extremely rapid development was headed by Adalbert Lohmann, who was later in charge of the development of the Bernhard/Bernhardine system. The new system operated in the 30-33.3 MHz band, i.e., a wavelength of 9 - 10 m. Obtaining a sufficiently narrow equi-signal beam at these frequencies required an antenna system with two large dipole arrays. The ground stations of this directional-beam system ("Richtfunkfeuer") were Telefunken Funk-Sende-Anlage ("radio transmitter installation") FuSAn 721. Their German code name was "Knickebein". The interlocked Morse code "E" (= "dot ", "•",) and "T" ( = "dash", "─") pulses were modulated with an 1150 Hz tone [per Trenkle/Funkführungsverfahren p. 129; = standard approach beacon TX]. The "E" dots were 1/8 sec wide, the "T" dashes 7/8 sec - the same as the standard Lorenz blind landing system. This way, the off-the-shelf transmitters (with integrated E/T keying) of those landing systems could be used.

Name: "Crooked leg" and "Knock-Knees" are the popular version of the generic medical term "angular limb deformity" (ALD). A.k.a. "X benen" ( = "X-legs") in the Dutch language, as opposed to "O benen" = bowlegs. Primarily used for an alcoholized egg yolk based drink, that supposedly knocks you off your feet. "Dog leg" - dog lifting a hind leg when urinating.

Simplified "X-Verfahren", could be considered as two long-range, high-accuracy, Lorenz landing beam systems (see below).


Accuracy: 150 m over target in England vs. 2 km over London per ref. 230Q6 (1940).

By the end of 1939, two Knickebein installations were operational along the western border of Germany: station Knickebein-2 (K2) at Stollberg/Bredstedt on the North Sea coast in the far north (later the location of Bernhard station Be-9), and K4 at Kleve (the German town that is closest to London and the Midlands). K12 was constructed during the winter of 1939/1940 at Maulburg (near Lörrach, in the far southwest of Germany, near the German/Swiss/French border. All three stations in Germany were the large Knickebein version ("Großanlage", "große Bauform").

Knickebein locations

Fig. 7X: Table with the location of all Knickebein stations

(the exact map coordinates of all Knickebein stations are provided in ref. 230Q1, incl. maps, aerial & satellite images)

Knickebein locations

Fig. 71: Map showing the location of all Knickebein stations (modern-day political borders)

(see ref. 230Q1 for exact coordinates and associated aerial photos & satellite images; an interactive Google-map version of this map is here)

The exact map coordinates of all Knickebein stations are provided in ref. 230Q1. I have also made a full-size interactive Google-map version of this map is available here. It has the same station locations markers. In most cases, you can fully zoom-in the satellite image map, and see the actual remains of the station structures. Click on any marker icon in that map, to get the associated information. You can click-and-drag the map with your mouse, and zoom in & out with your mouse-wheel (or use the buttons in the bottom left-hand corner of the map). Note: you must have maps.googleapis.com enabled in your browser.

To point the guide-beam at a bombing target in Britain, the system could be rotated on a circular track (diameter 96 m per ref. 5B, 94 m per ref. 230Q3). This large circular track was not a railway rail, but a single flat steel band on a concrete ring (a curved I-beam, embedded in the concrete; see Fig. 75B below). The outer vertical trusses of the frame were mounted onto a small platform, with a single line of multiple small support wheels underneath. The track diameter was somewhat smaller than the span of the truss frame. Likewise, the center vertical truss was supported by small wheels on a small circular track. See Fig. 71A. I have no details about the electrical motorized rotation drive system.

Knickebein large

Fig. 71A: Large Knickebein K2 at Bredstedt/Germany - under construction (replaced by Bernhard Be-9 in 1944)

(source: Fig. 36 in ref. 181; red circle shows the size of a man; also used in ref. 2C4, but erroneously referred to as "Kleve", which is K4)

Knickebein large

Fig. 71B: The fenced-in Large Knickebein K2 at Bredstedt/Germany - construction completed

(source: p. 9 in ref. 261L)

The "E" and "T" beams were offset by 7.5° to the left and to the right, respectively, of the direction perpendicular to the plane of the large truss frame. This created a narrow zone where these sub-beams overlapped in such a way, that they had the same field strenght. This equi-signal zone was about 0.3º wide. Looking at the antenna system from above, it had a slight V-shape ("crooked leg", "dog leg") of 180° - 15° = 165°. Note that the large steel truss box frame is completely straight! One of the two 7.5° angles is easy to see at the top left-hand corner of the dipole array in the photo above. The same angle is easier to see in photos of the Small Knickebein (Fig. 75 below).

Knickebein large

Fig. 71C: Large Knickebein K12 at Maulburg near Lörrach/Germany - under construction

(source: ref. 230Q2)

After the invasion of their neighbor countries, the Germans installed another nine Knickebein stations along the coasts of southern Norway (1x), The Netherlands (2x), and France (6x, from the Channel coast down to Brittany). Construction of station K13 on the isle of Sicily/Italy was advanced, but never completed or operational. These were Small Knickebein ("kleine Bauform", "Kleinanlage") systems. The rotable installation had a width of about 45 m, and a track diameter of 31 m. and had a single row of 4 dipoles plus "reflectors" per sub-beam, instead of 2x8. I.e., only one quarter the overall size of the Large Knickebein. Hence, the width of the equi-beam was larger (≈0.6º) and the side-lobes were stronger. These small stations were installed closer to their targets than the large K2, K4, and K12 stations in Germany. So, over the target location, the width of the equi-beam was still acceptable.

Small stations usable both as main guide beam and crossing beam.

Knickebein klein

Fig. 75A: Small Knickebein station (left: under construction in France, August 1941, possibly K6 (location: see ref. 230Q1))

(sources: Bundesarchiv Bild 101I-228-0322-04/Friedrich Springorum/CC-BY-SA 3.0 (left) and Fig. 37 in ref. 181)

The left-hand photo in Fig. 75A above clearly shows that the "reflectors" are indeed driven dipoles - see the split between the upper & lower dipole halves. So, they are "active", i.e., powered by the transmitter, and not passive ("parasitic")reflector rods.

Circular track: spoked wheel; a curved steel I-beam, either embedded in a concrete ring, or attached with regular rail-chairs onto wooden cross-ties (UK: "sleepers") on a track bed of crushed rock or gravel:

Knickebein klein

Fig. 75B: Circular tracks of the Small Knickebein K10 at Sortosville/France (left) and K13 at Noto/Italy (summer 1943)

(source left image: normandy1944.org.uk, accessed 31 July 2020; right image: ref. 90-TBD!!!!)

The Large Knickebein installations K2, K4, and K12 had an enormous rectangular antenna system, see Figure 71. The rectangular steel truss frame measured ca. 95 x 30 m (WxH, ≈310 x 100 ft). The center vertical truss divided the antenna system into two sides - one to generate the "E" sub-beam and one for the "T" sub-beam:

  • Each sub-beam was created with a large array ("Gruppenantenne") of vertical dipoles. All dipoles had the same 1λ length. For the operating frequency of 30-33.3 MHz, the wavelength λ is about 9.5 m.
  • Each array comprised two rows of eight vertical dipoles, one row right above the other. I.e., a "stacked array". These parallel dipoles were spaced horizontally by a standard ½λ.
  • Each of these dipoles had another dipole right behind, at a distance of ≈¼λ. These were not passive reflector rods, but active dipoles, driven by the single transmitter. This makes for more effective side-lobe reduction (see, e.g., p. 71 in ref. 137A).
  • The dipoles and reflectors were made of large-diameter metal tubes instead of wires, see Fig. 71B, 75. A larger radiator diameter makes an antenna more broadband ( = usable over a wider frequency range, without the need for "re-tuning" the system).

The Small Knickebein installations (K1, K3, K5-K11, and K13) also had a symmetrical antenna system with a 165°/15° angle, but a lot fewer dipoles:

  • Again, each sub-beam was created with an array of parallel vertical 1λ dipoles, with ½λ horizontal spacing.
  • But now, there were only four dipoles per side, not eight!
  • Also, each array comprised only a single row of dipoles, not two vertically stacked rows.
  • Here too, each dipole had another dipole right behind it, again at a distance of ≈¼λ.
  • As a result, the frontal area of this antenna system was only one quarter the size of that of the Large Knickebein.

The diagram below shows the configurations of the Large and Small Knickebein antenna systems:

Knickebein antenna configurations

Fig. 7x: Dipole array configurations of the Large and Small Knickebein antenna systems

(both systems are drawn to the same scale)

The radiation pattern of the K-stations was checked in detail. Ref. 230Q5 provides maps for the large K4 station at Kleve-Materborn. Some 300 field-strength measurements were taken on the western side of this station ( = direction England), at a distance of 3.6 - 18 km, and on lines close to perpendicular to the general direction to Engand. Most measurements are spaced by only 40-50 m (≈130-165 ft), which implies an angular resolution of about 0.15 - 0.72 degrees. Some of these measurements were taken as late as January of 1942!

Knickebeincheck points

Fig. 7XX: Some radiation pattern check points for K-4, marked with red dot & red number, with field strength in green

(Source: adapted from ref. 230Q5)

There are several Knickebein-beam radiation pattern diagrams floating around in literature, without reference to any reputable source. As always: trust, but verify! This is why I decided to create a simple model of the large Knickebein antenna array myself. I always use the fabulous 4NEC2 antenna modeling freeware tool. The complete antenna system comprises two independent identical arrays side-by-side (one for the dash-beam, one for the dot-beam), but only one beam transmits at a time. So, I only modeled one sub-beam. The results are shown below. Note that, as is standard for radiation pattern diagrams, a logarithmic scale (decibel, dB) is used for the signal-strength (see far left side of the two figures below).

Knickebein pattern

Fig. 73: Top, oblique, and side view of the radiation pattern of a Large Knickebein sub-beam ("E" or "T") - in free space

(the NEC file of my 4NEC2 model is here - it is not optimized)

The views above are actually quite similar to the generic patterns shown in other publications. However, they are only valid for an antenna in so-called "free space". I.e., without any objects anywhere near, or ground below, the antenna. This is unrealistic, in particular for an antenna system close to the ground (in terms of the number of wavelengths λ of the transmitted signals), as is the case with Knickebein (with λ ≈ 9.5 m). The figure below shows the impact of ground reflections (assuming conductivity and dielectric constant of standard "real ground"), clearly beyond the modeling capabilities of the era. My model does not include the steel trusses around the Knickebein arrays, which could cause some pattern distortions. In practice, this was "not disturbing" (pdf p. 4 in ref. 184F1).

Knickebein pattern

Fig. 74: Top, oblique, and side view of the radiation pattern of a Large Knickebein sub-beam ("E" or "T") - over ground

(the NEC file of my 4NEC2 model is here)

As illustrated above, the antenne array of the Large Knickebein comprises two stacked rows of vertical dipole antennas. The second row does not significantly change the radiation pattern. However, the overall transmitter power is divided 50/50 between the two rows. I.e., each row only gets half the transmitter power. This is not the case with the Small Knickebein: the full transmitter power goes to a single row of dipoles. That row comprises only half the number of dipoles of its Large counterpart, which concentrates less radiated power into the forward lobe of the pattern: less directivity. This makes the resulting sub-beam and equi-signal beam about twice as wide as those of the Large Knickebein. For the installation locations of the Small Knickebein stations, this reduced performance was still sufficient, at much reduced cost, size, and construction time.

Knickebein pattern

Fig. 7X: Comparison of a Large & Small Knickebein sub-beam ("E" or "T") - in free-space & over ground

Knickebein beams Knickebein beams

Fig. 72: The alternating "E" (dot) and "T" (dash) beams of the Knickebein beacon

Knickebein E/T sound - audio file still to be created...

Simulated sound of "Knickebein" meandering  across the E-beam, Equi-Signal, and T-beam

(source: ©2020 Frank Dörenberg)

On 21 June 1940, an aircraft of the RAF Blind Approach Training & Development Unit (BATDU, replaced several months later by the Wireless Intelligence Development Units, WIDU) intercepted Knickebein signals with a Hallicrafters model S-27 VHF superhet receiver (27.8 - 143 MHz), and determined the direction of their source. Ref. 5, 230D. During the winter of 1940/41, the Knickebein system became increasingly unreliable and unusable over Britain, due to jamming by the British. Reports on "spoofing" and "beam bending" by the British being undetected and effective are contradictory (e.g., ref. 5 vs. §27-28 in ref. 6D). The jamming tone pulses sounded different from the true Knickebein pulses (§28 in ref. 6A), possibly due to better keyclick suppression in the jammer. Also, the British jamming systems were incapable of synchronizing to the Knickebein pulses, hence, their jamming signals created easily detectable "wailing" beat tones. The system continued to be used in the lead aircraft ("Pfadfinder") for navigation towards the target, but those now relied on the X-System (described above) to locate and mark the actual target. In September of 1941, the Luftwaffe aircraft receivers were upgraded from FuBl 1 to FuBl 2, which supported a large increase in the number of available frequency channels in the same band, and a range of 600 km at 6000 m altitude (20 thousand feet).


  • Since standard E/T system, based on Lo AFF, used standard 500 W landing beacon transmitter ("Landebakensender") = Lo AS4, ...?
  • Human ear, fly not on the center of the beam but right on the edge, where it is easier to detect deviation (ref. ADIK???); 0.2-0.3 dB - but only in absence of background noise. UKW Fernfunkfeuer - VHF Long-Range Beacon
  • Zyklop (Cyclop): §28-30 in ref. 6G: "This was the latest form of the well-known Knickebein, working on 30 - 33,3 mc/s and received by E.B.L.3 in the aircraft. It was a mobile station which could be fully erected into operation within a week. 120 watt transportable beacon station, derived from Knickebein (late 1943, per ref 6G), operated on Knickebein frequencies, but range of 300-350 km vs Knickebein 450 km.
  • A still more mobile unit known as the Bock-Zyklop had been introduced, operating on FuG16 frequencies ( = ???? MHz, VHF). Ref. 6G §29. This could be set up in three days and could be adapted for use on the FuGe 16 frequency although as yet, according to documents, no visual indicator for the FuGe 16 had been developed. The 120 W ground transmitter was called the ???? which gave a beam 0.5° wide and a range of 300 km. at a height of 5,000 meters. The Zyklop systems had been made use of on the Russian [also near Borisow/Belorus?] front up to the end of the hostilities. Ref. 6D, §41: It was developed by Dr. Künhold at Köthen [see above in Xsystem section; add bookmark link]. Ref. 2C1: 1940/41, "Zyklopfeuer" FuSAn 722 ground station + FuBl 1 / FuBl 2 airborne radio set.
  • There are some references (e.g., AIR 14/2343, AIR 14/3246) to Knickebein stations (e.g., K3) being reactivated starting December 1943 - not for guidance of Luftwaffe bombers, but of fighter aircraft for intercepting Allied bombers arriving from Britain. British codename: "Ottokar". This is unconfirmed by original German documents. E.g., there is no mention such a procedure in the Kriegstagebuch (KTB, War Diary) of the I. Jagdkorps (1st Fighter Corps, responsible fighter units within the Reich). Technically, it would have been possible to point a Small Knickebein beacon at a bomber stream, scramble fighters on a vector to intercept the beam and inform the fighters of the direction of the beam.


Already in 1939, an other successor to the "X-System" was conceived. It retained the director-beam ("Marschleitstrahl") concept of the "X-System". But rather than using a cross-beam to mark the position of the target along that beam, it used a transponder system (?? "Emil" Kontroll-E-Messung???) that allowed the ground controller to determine the aircraft's distance from the beacon (of course "slant range", not distance over ground). After a fixed delay time, the transponder in the aircraft would retransmit the received signal at a different frequency (1.9 MHz lower). The interrogator ground station would derive the range from the total round-trip signal delay, minus the fixed delay. The ground controllers would command release of the bombs ("Abwurfkommando", based on the range, via VHF R/T. This was called the "Y-System" ("Y-Verfahren", ref. 6G, 244D), US/UK Allied code name "Benito" (system or beacon?). It became operational in September of 1940. As the procedure involved a ground controller, the number of aircraft that could use the system simultaneously, was limited.????

Why "Y"? Successor to "X"?

Ref. 6D, §29, 30: Like X-system beam nav, Y-system also conceived by Plendl but developed at the Technisches Amt instead of at Köthen.

Ref. 6L.

Ref. 185C.

As with the "X-Verfahren" above, ,we have to get some terminology straight, as there is some general and persistent confusion, particularly in non-German publications.

Y-Verfahren ("Y-Procedure"), Y-Gerät ("Y-Equipment"); the "Y" beam-guidance-to-bombing target method is not to be confused with "Y-Verfahren" procedure for guiding fighter aircraft to intercepting enemy aircraft (ref. 244R), with its Y-stations/Y-sites (ref. 6E) incl. Y-Peiler ("Y-D/F system"), nor the British Y-Service! The "Y-Bake" ground station was called "Wotan II" (FuSAn 733). Not to be confused with "Y-Bodenstelle", "Y-Peiler", ref. 6E "Equipment of a Y-Site", ref. 244R ??? "Y-Procedure for fighers", which used a variety of transmitters was used (Bertha I, Bertha II), and a number of co-located transponder transmitters (Y-Stations in Germany: Sender 16 Boden / S16B, Y-stations in France: "Société Anonyme des Industries Radioélectriques" Sadir 80/100; Elsewhere any?).


The British "Wireless Interception" service (WI-service, phonetically abbreviated to "Y" service) was responsible for the monitoring of enemy radio transmissions. The radio-intercept stations were known as Y-stations. The service dates back to WW1, and was run by the Royal Navy: Naval Intelligence Department I.D. 25, also known as "Room 40". In 1920, the service was transferred from the Navy to the Foreign Office (FO), and "Room 40" was renamed to Government Code and Cipher School (GCCS). In 1939, the GCCS moved to Bletchley Park (BP) in Milton Keynes/Buckinghamshire (about 80 km / 50 miles north-west of London), and was renamed to Government Code Head Quarters (GCHQ). Ref. 35.

During WW2, the Y-service covered radio-telephony, Morse telegraphy, and Non-Morse (NoMo) transmissions, whether encrypted or not. NoMo traffic included teletype/teleprinter and Hellschreiber. The Y-stations were operated by a number of government agencies (the branches of the armed forces, the Metropolitan Police, and the General Post Office) and the Marconi company. Some stations only had direction-finding (D/F) capability.

During the course of WW2, the service grew from a few Y-stations, to a global network of small and large stations. They were located in the UK, the Middle East, Far East, North Africa, mainland Europe, and offshore. Intercepted encrypted signals were either analyzed locally, or transferred (by dispatch riders on motorcycle or via teleprinter) to BP. Sometimes BP is referred to as "Station X" (i.e., station nr. 10), though that actually refer to a small Special Intelligence Service (SIS) wireless station (MI6 Section VIII) that was originally located at Barnes in west London (south of the Thames), and temporarily moved to BP.

The (lead / Pathfinder) aircraft required a "Y-Appraratus" ("Y-Gerät") installation (ref. 2A, 6E, 229P, 230R1, 230R3). This comprised:

  • One dedicated beacon receiver: the "UKW Leitstrahlempfangsgerät" FuG28a, comprising:
  • A slightly modified E17 receiver of the modular Lorenz FuG17 VHF radio-telephony transceiver "UKW Sprechgerät" (42.15 - 47.75 MHz, 10 Watt, ref. 40C). Manufacturers of the E17 include "Dr. Georg Seibt A.G." in Berlin; plus (dedicated or shared?) ca. 1 m long rod antenna ("Stabantenne"). Seven stage, tubes: 9x RV12P2000. Weight: 5.3 kg (incl. tubes), 138x210x205 m (WxHxD)
  • An AW28 "Auswertegerät" / "Bakenwandler" - signal processing / interpretation unit (e.g., for converting received audio signals from course-guidance beams (e.g., E/T pulses from Lorenz Landing beam, Knickebein, X-System, Y-System) left/right course-deviation signal to drive a lateral auto-pilot. An electro-mechanical (?) equivalent of the X-system's AVP unit ?
  • AW28 manufacturer, based on Fertigungskennzeichen mfr code "ded" on equipment label (see Fig. XX): "Heliowatt Werke, Elektrizitäts-Aktiengesellschaft" factory in the town of Schweidnitz (Świdnica) in Silesia (post-WW2 south-central Poland). Heliowatt was originally established by Hermann Aron in 1897 as a subsidiary of "H. Aron Elektrizitätszähler-Fabrik GmbH" in Berlin-Charlottenburg, renamed "Aron Elektrizitäts GmbH" in 1912. The "Aron" name was Germanized in 1933 to "Heliowatt". Already in 1923, Aron had begun to produce broadcast radio receivers under the ethnically-neutral brand name "Nora" ("Aron" in reverse). In 1935, the company was aryanized (i.e., expropriated for ethnic reasons) and sold off to Siemens.
  • An LKZG ("Leitstrahl-Kurssteuerungs-Zwischengerät") to interface the FuG28a to the lateral-mode autopilot ("Kursregler"), for automatically tracking an equi-beam,
  • One course-deviation indicator (CDI): "IJ 28" (Bauart: Siemens Apparate und Maschinen GmbH (SAM), Mfr: Philips in Berlin, see below).
  • Alternatively ?: AFN2 ("Anzeigegerät Flug-Navigation"), see Fig. 45A.
  • Unclear how IJ 28 was connected to the FuG28(a), as a converter unit would be necessary. Per L-Dv-702-1-Heft-205 (Anlage 4), FuG17 included a "Nav-Gerät", which could connected to the E17 "Tel." headphones output.
  • One FuG16ZE or FuG16ZY transceiver (38.5-42.3 MHz and 38.4 - 42.4 MHz, respectively; ref. 40A, 40B; other differences?), 1.9 MHz transponder shift; used by Y-station for D/F.
  • "Y-Messung" w FuG 16 ZY ("Fugb-S XVI Z/ZY", Fugb-S-XVI-Z-ZY.pdf) 38.4-42.4, VHF, E-Mess range ca. 80% of VHF com range which was 30-320 km at - 300m - 10km alt) Unabhängig vom Nachrichtenverkehr kann das Flugzeug von einer E-Meßstelle aus über das FuG 16 ZY angemessen werden (Y-Verfahren); Tagjäger, Nachtjäger = Y-Kampf version of Y-Verfahren.
  • Also used the "X-Uhr" clock. Top lever pushed at certain ranges from the target (based on xpdr range (call out - tbc), at the range where an X-system would the VS  crossing-beam pre-signal or HS crossing-beam main-signal.Before the actual release, a warning signal ("Bombenabwurfsignal") is sounded (sent by the ground station): a sequence of dots-and-dashes tone pulse sequence, equivalent to the Morse code "SMS" = • • • ─ ─ • • •. The first and last dot were spaced by 9 seconds. The final dot signified the actual "bombs away" command. See Trenkle "Funkführungsverfahren" p. 149/150.
  • Associated power converter units, to provide the receivers and transponders with the required DC supply voltages.
  • Various control panels.


Fig. 50A: Front of the FuG28a "UKW Leitstrahlempfangsgerät" (VHF guide-beam receiver)

The yellow stripe across the front of the above AW28 unit was the standard method to mark a "Formänderung" - a modification, without model designator change.

(source FuG 17 image: deutscheluftwaffe.de)


Fig. 50: View into the top of the FuG28a

(source: www.cdvandt.org)

As the suffix "28" implies, the IJ 28 was specific to the FuG 28.

FuG28 IJ28

Fig. 50B: A 1942 course-deviation indicator model IJ 28 of the FuG 28 system and label on the housing of the unit

(source left & center image: eBay article nr. 383651899889, 2020)

The equipment label states that the IJ 28 was designed by Siemens Apparate & Maschinen GmbH (SAM) in Berlin (most likely the SAM Luftfahrtgerätewerk Hakenfelde (LGW) in Berlin-Spandau). The label lists Philips in Berlin as the manufacturer. The Dutch company Philips Gloeilampenfabrieken N.V. established a German national subsidiary Deutsche Philips GmbH in Berlin-Mitte in 1926. Late 1935, the company created a special department: "Kathograph". It developed and manufactured measurement instruments ("Kathodenstrahl Oszillograph" = cathode-ray oscillograph) and TV's at the central Philips-Haus offices at Kurfürstenstraße 126. In March of 1937, this department was incorporated as Philips-Electro-Special G.m.b.H. Berlin (PESB). After WW2, it was reestablished in Hamburg as "Elektro Spezial GmbH" (1949).

The bottom part of the glass of this instrument (and other serial numbers) has a large black crescent painted on the inside. Unclear what it covers up. The unit's rear connector has two pins for the moving-coil meter.


An interesting beacon system is the Hermes/Hermine "Sprechdrehbake" system ("rotating talking beacon"). The system was originally developed in response to a tactical requirement formulated during the second part of 1942, as a navigational aid for the purpose of giving an approximate bearing to single-engine night fighters engaged in "Wilde Sau" [lit. "Wild Boar"] air-defence operations. The pilot could determine the bearing from the beacon, without having to look at an instrument. The beacon stations (FuSAn 726) transmitted real-time voice-announcements of the beam azimuth, every 10º. I.e., the numbers 1 - 35 (multiples of 10º, as standard on compass scales), and the "station call-sign" at 360º = 0º = True North passage. Each digit was pronounced separately: e.g., "12" = "1-2" (as is proper /standard practice in worldwide aviation radio comunication to ensure intelligiblity, except in France), not "twelve". The voice stream was pre-recorded as an optical track on an endless/continous film strip ("Tonfilm") + photoelectric cell; rotated with the shaft of the antenna system (--> "optical disk"?). The voice signal was transmitted (FM modulated) with an omni-directional antenna. At the same time, and on the same frequency, a strong constant audible 1150 Hz tone was transmitted. However, it was transmitted with a rotating cardioid antenna pattern. The null of this pattern ( = no 1150 Hz interference signal) coincided with the direction as announced by the voice announcement at that very moment. So, the voice could only be heard (briefly) in that particular momentary direction. Due to the width of the null (effectively about 15° (ref. 8), equivalent to (360°/15°)x60=2.5 sec), the immediately preceding and following announcement was only partially audible, at much reduced volume.

The airborne counterpart, FuG125 "Hermine-Bord", comprised the standard EBl 3 receiver, its FBG2 control panel, and a small audio-amplifier (model V3a or ZV3), (separate?) FM demodulator.


  • The system was developed in 1943/44 by Ernst Kramar et al of the Lorenz company.
  • Ref. 164B (pp. 13-15): antenna system atop a 16 m tall steel tower, accuracy ~2°, headphone in a/c, transmitter 150 W type AS3 (Lorenz landing beacon TX), 30-33.3 MHz (HF/VHF); antenna system had gain of single dipole; configuration: 2 pairs of vertical dipoles at 4 corners + 1 central omni for voice announce; antenna current ratio dipole pair-1 : pair-2: omni = 1.0 : 1.8 : adjusted to min (?); bandwidth +/- 0.5 MHz without changing length of the 4 outer dipoles  (30-33.3. MHz when changing length); antenna system mechanically rotated at 1 rpm; feedlines through hollow shaft --> slip rings; noise transmission turned of during station ID announcement (1100 Hz, not 1150?); single/same transmitter for tone and voice? ; monitoring w aircratf type RX at 200-300 m, with audio via telephone cable to control/equipment room. Hermine/FuG125 had to be minor modded to increase audio bandwidth (with add'l on/off ctl).
  • Ref. 229Q, p. 92: cardioid pattern.
  • Ref. 185H: Yet another receiver was developed by the Lorenz Company (Dr. Kramar) which was designated FuG 125, code named “Hermine.” The receiver was made up of the EBl 3 F receiver, the FBG 2 remote control, a V3a amplifier for volume control. A FuG 16 ZY antenna was connected in parallel. This unit was designed for IFR weather. On the 14th of September 1944 an order of 18,000 units was given to the Stassfurter-Rundfunk-GmbH [Staßfurter Rundfunk-Gesellschaft mbH, the 1932 radio production subsidiary of Staßfurter Licht- und Kraftwerke AG]. In the last part of the war only a few dozen units were delivered and used in the Me 109, Fw 190, Ta 152, Do 335 and 15 Me 262
  • Ref. 6G §58-64: The Hermine system was originally developed, in response to a tactical requirement formulated during the second part of 1942, as a navigational aid for the purpose of giving an approximate bearing to single-engine night fighters engaged on “Wilde Sau” operations. By the time the initial difficulties in development had been overcome Wilde Sau night fighting had almost ceased; it was found however that Hermine could be used to advantage by day fighters, and it came into operational use. 60. An accuracy of ±5° was assumed, but it was found in practice that this could be improved upon to ±3° by experienced pilots. Thirteen or fourteen ground stations were in operation by Easter 1945 which, P/W claimed, gave complete coverage of the Reich. It was intended to fit two Schlechtwetter (bad weather) Fighter Geschwader with the necessary airborne equipment, and this program had been one-third completed by May 1945. One P/W had heard that ten to fifteen Me.262's of K.G.51 were amongst the aircraft so equipped. The following may be added in modification of the description of the Hermine system given in A.D.I.(K) 125/1945 [ = ref. 6C] , paras.59 to 62. The Hermine rotating beacon transmits a continuous tone on which is superimposed a speaking clock which counts from 1 to 35, each figure representing tens of degree. Over an angle of about 15° the continuous tone falls to a minimum and rises again. During this period the voice appears to become more audible and the pilot can estimate where the minimum of continuous tone occurs, and so obtain his bearing from the beacon. The beacon recognition is given by means of a self-evident code name for example, "Berolina” for Berlin – which is spoken by the voice in place of 000°. The airborne equipment is the FuGe 125 consisting of the E.B.L.3 with the Tzg (Telephoniezusatzgerät) which enables the 30.0 - 33.3 mc/s transmission picked up on the E.B.L.3 receiver to be heard in the pilot's headphones. Though the Hermine beacons were fully operational there was a scarcity of FuGe 125 sets, as a result of which practical experience of this system was too limited to judge of its efficiency or to lead to further improved tactical requirements been formulated.
  • Ref. 2A; 2C4, p. 128: Range 200-250 km at 15000 ft. Accuracy 3-5°. Antenna system: 4 vertical dipoles with "Drehfeldspeisung" at 4 corners of a square with 1/8 λ sides, plus a central radiator (vertical dipole?). Antenna system rotating at 1 rpm. Purpose: enable fighters to home to airfield. Five beacons operational in January of 1944, 13-14 by Easter of 1945, spread out over the Reichsgebiet. Receiver: Lorenz FuG 125 "Hermine" = E Bl 3 F [F = Fernbedienung = remote control] + Zwischenverstärker ZF 3 amplier + Anzeigezusatz[gerät] ZuG 125 + one AFN2 [see Fig + text above, add #]. Airborne receiver shared antenna with the VHF R/T transceiver FuG 16 ZY.


Fig. 51: Principle of the "Hermes/Hermine" talking beacon system

(source photo: deutschesatlantikwallarchiv.de)


Fig. 53: Radiation pattern of the rotating "null" beam

Hermes sound - audio file still to be created...

Simulated sound of a "Hermine" beacon (60 sec rotation)

(source: ? © ? used with permission)


Consol sound

Sound clip of a Sonne/Consol sequence (42 sec)

(source: de.wikipedia.org, retrieved March 2020)

Consol sound

An other sound clip of a Sonne/Consol sequence (3 min)

(source: www.geocaching.com, retrieved March 2020)


GB: Gee/G/Grid, German Á copies/compatible system; US derived system (LORAN); German experimental pulse hperb system "Ingolstadt" (originated by Telefunken, 1938

hyperbolic system

Fig. YY: The hyperbolic radio navigation system for aviation

(source: National Air & Space Museum, Smithsonian Institution, "Time & Navigation - Navigating in the Air", 2012, artist: Bruce Morser)

Video 1: Short version of the 1947 "LORAN for Ocean Navigation" clip produced by the US Coast Guard to promote LORAN to commercial shipping lines

(source: Smithsonian National Air and Space Museum, also YouTube)

Loran sound

Sound clip of Loran/Loran-A pulses (33 sec)

(source: A. Cordwell, retrieved February 2020)


Circular LoP.

Radio-transponder based ranging (here: range in sense of distance) invented and patented in France FR632304 & GB GB288233 in 1927 by Alexandre Koulikoff & Constantin Chilkowsky.

WW2 Germany + UK/GB.

Derived from "Identification Friend or Foe" (IFF), ground-based interrogator + airborne responder or transponder. Reverse roles: airborne interrogator + ground based transponder.

1944 Convention on International Civil Aviation (also known as Chicago Convention), looked at developing a form of distance measurement, based on the Rebecca-Eureka ‘Identification Friend or Foe’ (IFF) secondary radar system, and operating in the 200 MHz band. Adapted to DME(A) in Australia in 1946.

1945 CERCA London meeting

"Up to that time whilst continuous azimuth guidance on airways was provided by various types of radio beacons, progress along track could only be measured by station passage of a beacon - in other words, by flying over it."

200 MHz DME(A) Australian (Modern version was (re-)invented in Australia 1944/45 (Brian Cooper vs James Gerrand?), AWA early 1950s,  discontinued December 1995). US-pushed/ICAO/Int'l 1000 MHz DME(I), ca 1964.

  • interrogator + responder/transponder (transmitter-responder)
  • Invented and patented in 1927 (Koulikoff + Chilkowsky). = Transponder-based ranging = analog DME
  • Slant range, time-of-fligh (as radar)
  • Ground-based/fixed-base/stationary interrogator + mobile/airborne responder/transponder: WW2: IFF, E-Meßung. Modern: secondary radar, transponder.
  • Responder vs transponder: TBC reply on interrogator freq vs offset frequency channel.
  • Example: UK/RAF/WW2: Rebecca (airborne interrogator; name supposedly derived from "Recognition of Beacons") + Eureka (gnd based xpdr, since freq shift; fixed DeltaT --> min range of 2 milles; coded pulsed reply; A coding unit which is part of the Eureka beacon periodically causes the width of the beacon response pulses to vary at Morse code intervals for identification. This function may also be manually controlled for transmission of simple messages.), developed by TRE (frmr AMES research ctr). Mk-I 1941, operational by 1943. Became integrated in BABS (E/T keyed VHF course beacon + xpdr; homing approach beam), PRF 300, 4-5 usec pulses, 170-234 MHz Mark X: 1 GHz), slant-range determined from round-trip time-of-flight with radar display pulse scope (time-base synced to TX). Many equipment variations built, US-built versions: AN/PPN-1 (fixed), AN/PPN-2 (portable), AN/TPN-1 (xprtable) xpdr. AN/APN-2 (interrgtr) aka SCR-279. Rebecca-H (for use with 2 xpdrs) used in combo with Gee-H.
  • Ref. 265A.
  • FuG25a ; a complete key has 10 tabs that can be broken off to create a Morse-code tone-pulse sequence; the FuG 25 used two selectable keys: Reichskennung (roaming, without/before/after performing unit/squadron specific instructions ("Befehle") + Verbandskennung = Unit/Squadron key). Xpdr reply code, in more modern ATC parlance: squawk-code. Key tabs actuate (open?) cam switches. Keys only exchangable before fligh / on ground. Ref. 244V: specific keys valid for limited time periods.

GAF IFF coding key

Fig. XX: Programmable reply-code key and coding unit of the Luftwaffe FuG 25 "Kenngerät" IFF transponder

(source key photo: Collectors Weekly, accessed December 2021; also see ref. 2C8; coding unit: ref. 261AA)

  • DME - Distance Measuring Equipment
  • Role of "interrogator" and "responder/transponder" reversed: airborne interrogator, ground-based (fixed/mobile) responder/transponder. Allows/supports independent airborne navigation.
  • Slant range, like radar.
  • Mobile/airborne interrogator + Ground-basedfixed-base/stationary responder/transponder: modern: DME, often colocated with VOR = VOR-DME or mil TACAN = VORTAC; To this date, still important nav aid, but being phased out slowly in favor of GPS?
  • IFF - Identification Friend or Foe
  • Add-on to the Xpdr functionality. Purpose. Selectable transponder reply codes.
  • Ref. 110M for a British view on its history.
  • Radio/radar altimeter: developed during 1930s in parallel in Germany (Siemens-Halske) and USA (esp. Bell Labs). Refs: 268A-268K.
  • Patents?
  • Nodal (e.g., E.F.W. Alexanderson/GE Co.: indicated position between nodes produced by transmitted and reflected radio waves.) vs FM (e.g., W.L. Everitt: FM ("carrier wave varied by rotation of air condenser"). Beat note of transmitted and reflected waves has pitch that is a direct function of the altitude) vs pulse
  • Height above terrain (vs barometric altitude, based on pressure difference wrt a reference pressure level [fixed, eg above 18 kft, or wrt local/regional altimeter setting = baro pressure at ground level (typ. airport/aerodrome)].
  • Difference Radio Alt (RA) vs Radar Alt (RadAlt).
  • Two modulation types: Frequency Modulation Continuous Wave (FMCW, triangular/sawtooth waveform "chirp" with fixed period and df/dt (rate), the second utilizes pulsed modulation. Frequencies: high enough to get usable echo from ground/terrain, i.e., ??? Both based on round-trip time-of-flight of transmitted signal, either as ΔfT x df/dt (RA) or ΔT directly (RadAlt)
  • FMCW: Separate TX and RX antennas (aka bistatic?). As with radars, several techniques to avoid interference between such altimeters. Modern: ca. 50 Hz, 150 Hz, 12-1600 Hz waveform repitition freq, TX power < 1 W.
  • Pulsed: single antenna as with radar, modern: 6000-20000 pps, TX power 5-100 W.
  • ICAO standard performance: accuracy 3 ft / 0.9 m or better
  • Challenges include: bank angle, "jagged" terrain
  • 1930s/WW2: USA: RCA ABY-1, RC-24; based on R&D since 1929/30 at Bell Labs etc. USA, UK, D, F,...
  • WW2: Germany, Luftwaffe
  • <= 1940: Funkhöhenmesser FuG-101/101 A (FM), Siemens/LWG, λ = 75-89 cm, 337-400 MHz, 1.5 W; ref. 268A, 268G. 268H. Subsequently/1944 same technology subsequently used in "Marabu" proximity fuses of ground-to-air/surface-to-air missiles.
  • FuG102, FuG103, FuG104 (smaller FuG103, never operational ?).
  • Siemens FuG101, FM (ref. 7A (section III c on p. 358-359)
  • Modern: stdrd ICAO frq range 4.2-4.4 GHz (RadAlt), height above terrain: upto 3000 or 4000 ft?
  • precision approach & landing aid (esp. auto-pilot coupled and in low-vis conditions), ground/terrain proximity awareness/clearance/collision avoidance (later GPWS/TAWS, highly significant contribution to flight safety)
  • Radio alt: 29Q, pp. 211ff
  • "Fallhöhenmesser" (beacon-probe drop altimeter) Ref. 7A (section III a on p. 358): Siemens, 1935-1938
  • Capacitive altimeters:
  • Ref. 7A (section III b on p. 358): Siemens, 1935-1938; ref. 235P35., pp. 208ff in ref. 229Q
  • Sonic altimeters
  • ref. 268J, 268K, ref. 229Q p.199 in chapter VII


This section only covers radar applied to navigation / guidance (fixed/ground-based: OBOE, airborne: H2S/X ground mapping - nav + ground target ID). Primarily: British/Allied?  I.e., not air-air intercept, not early warning, not FLAK, not gun-laying,...

Finally, after decades of shameful denial, the world-renowned IEEE finally redeemed itself in 2019. It formally recognizing that, contrary to popular belief, perpetuated Allied WW2 propaganda and general ignorance, radar was not only invented and patented in 1904 in Germany by Christian Hülsmeyer (patents 165546, 13170, 25608), but he also publicly demonstrated his "telemobiloscope"/"Telemobilskop"in Cologne/Germany (Köln), and in Rotterdam/The Netherlands that same year. Ref. 261A, 261B.

3 general categories: Earyl warning, Ground control, intercept, ..

The term "radar", for Radio Detection and Ranging, was actually introduced in the US  1940. UK: "Range and Direction Finding ", D: "Funkmeß" = lit. radio measurement

Types of Radars:
• Pulse Radar: time of flight-> range; transmit short pulses, measure echo delay; ref. 261A7.
• Doppler (CW) Radar: frequency shift -> velocity; transmit constant frequency, measure frequency shift due to (relative) motion
• Chirp (FMCW) Radar: frequency difference -> range; transmit varying frequency, measure how much frequency changed during echo delay


In addition to the beacon systems described above, there was a number of other German beacon systems (ref. 1, 2A, 8, 26B, 230A-230C, pp. 7-19 in ref. 164B), such as:

  • "Dezimeterwelle-Richstrahl-Drehfunkfeuer" a.k.a. "Drehbake M" (UHF rotating-beam beacon). Ref. 2B, ref. 2C4, p. 122; ref. 2A, p. 87ff: DVL/Plendl, 261-268 MHz carrier frequency [≈1.1 m, so not truely "decimeter"], variable azimuth-segment dependent modulation (5.3-6.0 kHz in the 270°-0°-90° semi-circle direction, 8.0-10.0 kHz in the 90°-180°-270° semi-circle) , 100 W telefunken magnetron transmitter. Transportable, mobile (truck), and fixed-base installations. Antenne system: broadside planar array (4 m wide) of 18 ½λ-dipoles (2 stacked rows of 9?) + as many reflectors behind them, motorized rotation 1 rps (60 rpm!). 3 test sites: Rechlin, Schneeberg (≈ 90 km northeast of Nürnberg (Nuremberg), ≈ 30 km from the Czech border; with 1050 m the highest peak in the Bavarian Fichtelgebirge mountain range), the Wendelstein (1836 m, peak in the Bavarian alps, ≈ 60 km southeast of München/Munich, close to the Austrian border). Associated on-board receiver system: "Dezimeterwelle-Funkfeuer-Empfangsgerät AF2/3" a.k.a. "M-Gerät", comprising Telefunken BFO receiver "Lina", a Siemens "Zusatzgerät", a Siemens "Anzeige-Meßbrücke" with "Peilwertanzeige", and a "Rollkarte mit Lichtzeiger" (per DVL/Hepper) moving map/chart with light-pointer. Alternatively: standard AFN1 kick-meter ("Zuckanzeige") indicator, as for Lorenz ILS and Knickebein. Planned: course setpoint selection and auto-pilot coupling. Achieved RDF and course-tracking accuracy: +/1 1° and range up to 500 km. Development halted spring 1939 in favor of "Erika", due to complexity (temperature & auto volume/gain control), some issues with side-lobes of the radiation pattern, and reflections from terrain (e.g., cliffs & montains).
  • Baldur, VHF system range measuring system (basically DME), comparable to British "G-H". ref. 6G. Airborne set: FuGe 126 and FuGe 126k "klein". Wavelenght: ca. 2-4m (75-150 MHz). Locations: possiblyonly 2 experimental stations in Lower Silesia (check Ln maps/charts) . Further developments (never operational):
  • Baldur-Truhe (combination of Baldur and Truhe)
  • Baldur-Bernhardine (combination of Baldur and Bernhard, for simultaneously obtaining bearing and range; with a "Bernhardine" Hellschreiber printer for bearing & range indication; ref. 6G: The range indication was to be obtained by the pilot pressing a knob when the range would appear in kilometres on a dial. This system was suggested for use by both day fighters and bombers.).
  • Elektra: long wave beam system (initially ca. 480 kHz, later 270-330 kHz), range over land 800-1200 km (500 and 300 kHz respectively), range over sea 1700-200 km (500 and 300 kHz respectively). Three antennas per beacon station. Transmitter power: 1.5 kW. Ref. 230A, 230B; 2C4, p. 121 etc.. Ref. 164B, p. 7: antenna height only 50 m and goniometer to swing the beam to the desired direction.
  • Stations (p. 6, 7 in ref. 164B): Huisen/The Netherlands (1940, 460 kHz, 10 λ spacing), Bayeux/France (Nov 1940, 300 kHz, 5.7 λ spacing, (temporarily?) dismantled late 1943); Stavanger (March 1941), Morlaix (?), one near Warsaw.
  • Elektra kurz (480 kHz, λ = 625 m; 1939-1941), Elektra lang (300 kHz, λ = 1000 m). Ref. 230K.
  • Dreh-Elektra? = Sonne?
  • Sonne ["Sun"]: long wave (several LF frequencies between 270 and 330 kHz vs 300 kHz nominal and 250-350 kHz), long-range system of the Kriegsmarine (navy). Lorenz. It was based on "Elektra", but rather than physically rotating a loop antenna, Sonne used three stationary antennas spaced about 1 km (about 3.86 wavelengths) and a single transmitter + goniometer, to electronically sweep the direction of the beams. Range over land 1200 km. Range over sea 2000 km. Transmitter power: 1.5 kW. Ref. 230A-230C, 230K1, 230K2, 230K3, 164B (p. 8, 9)). Collapsed hyperbolic system (extreme case of hyperbolic). Became operational June 1942.
  • Goldsonne. Ref. 164B, pp. 15-17: proposed by Dr Goldmann to overcome disadvantages of Sonne and Komet.
  • Goldwever/weber: a "Sonne" derivative that never became operational. Ref. 164B, p. 12: substitute for Komet. Ref. 38B.
  • Mond ["Moon"]: experimental system, intended to improve range and accuracy of "Sonne", while operating on higher frequencies (3 MHz, 6 MHz; 30-30 MHz per ref. 230A), at night. Ref. 2C4, p. 127.
  • Stern ["Star"]: an experimental Sonne derivative, operating at VHF frequencies, hence range basically limited to line of sight. Not developed to completion.
  • Esseker: Sonne derivative, with quicker indication of position.
  • Elektra-Sonne: beacon could be operated alternately as "Elektra" and "Sonne", to combine advantages of both. Range was intended to be increased by raising transmitter power to 60 kW. Three stations were built during 1944-1945 but were never operational. Ref. 230A. Bergen/Groet: ref. 278.
  • Erich: "UKW-Phasendrehfunkfeuer"., i.e., a VHF rotating-phase navigation system.
  • Fernmeldetechnisches Entwicklungslaboratorium Dr. Ing. H. Kimmel ("Development lab for telecom equipment") in Munich, later Münchener Apparatebau für Elektronische Geräte Kimmel GmbH & Co. KG. Their 3-letter military manufacturer's code was "bes". Kimmel also made the "NF Phasenuhr" (audio frequency phase-indicator, with 360º scale) that was part of the on-board equipment of the 1943 Lorenz VHF rotating-phase navigation system "Erich" (very similar to the VOR system developed in parallel in the USA). Like "Bernhard/Bernhardine", the "Erich" system also used the EBl 3 radio receiver.
  • Ref. 2A; 2C4, p. 128 . R&D at Lorenz started in 1943, on the familiar/standard 30-33.3 MHz freq, based on a 1940 patent (nr ???). Antenna system: 4 vertical dipoles at 4 corners of a square with 1/8 λ sides, plus a central radiator (vertical dipole?). The 4 dipoles were excited with a (standard) 500 W landing beam beacon transmitter, unmodulated carrier only, via motorized rotating radio goniometer [antennas stationary!]. Creates a cardoid, rotating at 50 rpm, resulting in a 50 Hz amplitude variation at the receiver, similar to 50 Hz AM modulation. Central (omni-directional ) antenna powered by a separate 10 W FM-transmitter with constant 50 Hz modulation, referenced to "North" passage of the rotating cardioid. Phase difference between the two received 50 Hz signals [after AM and FM demodulation, respectively] is [linearly] dependent on the bearing from the beacon to the receiver. The [demodulated signals where compared] with an "NF-Phasenmesser" / "NF-Phasenuhr" ["AF phase clock"] with two electric motors driving an indicator pointer w.r.t. a 360° scale, via a differential gear. See blockdiagram in ref. This system is very similar to the simultaneously and independently VHF Omni-directional Range (VOR) beacon [here too: "Range" is not "distance" but "directional beacon"]. For the given cardioid radiation pattern, the achievable accuracy was "only" 1°, and the fact that demodulators and cockpit indicator were needed,[and the industrial stage of the war], the project was cancelled in favor of the "Hermes/Hermine" "talking beacon", [with a slowly rotating "4 vertical dipoles + central omni antenna" antenna system] which only required the existing standard receiver.
  • Erika: a hyperbolic beacon system [TBC], comprising a line of six antenna arrays (spaced ca. 46, 18, 27, 27???, and 124 m) each with a transmitter. Similar to the British Gee system. Developed in 1942 (per ref. 164B p9: mid-1941 by Dr Goldmann / Lorenz), briefly operational, replaced by Bernhard. Ref. 8. Developed by P. von Handel, Pfister (who proposed the 6 antenna solution) @ DVL, et al.
  • Ref. 230K1, 164B.Ref. 2C4, p. 125-127.
  • Ref. 20: accuracy obtained ≈0.015°, avoided HF phase measurements by converting HF phase to NF phase via "umlaufende Interferenzlinien" ("circular interference lines" ???). Transmitter station comprised three dipole pairs. Dipole pair #1: excited with f1 and f1 + Δf, respectively. The combined waves fronts create interference lines that are modulated with Δf, such that at all points in the coverage area, a signal with the carrier frequency f1 that is wobbled (sweeping FM modulated) with the beat-frequency Δf is received. Transmitter 2: dipole pair #2: similar to pair #1, but excited with f2 (close to f1) and f2 + Δf. Lines of constant phase difference are hyperbola. At the receiver station, 2 receivers are required: tuned to f1 and f2, respectively. The audio output of each receiver drives a small synchronous motor. The 2 motors drive a differential gear, the output of which moves a pointer that indicates the momentary phase difference between the beat-frequency wobbles about f1 and f2. To be able to determining position (by intersecting hyperbolic LoP's), f3 and f3 + Δf were transmitted via a third dipole pair. On-board equipment comprised 4 receivers and 2 Phase-clocks; or: 2 receivers (with the tuning of the second one switched between f2 and f3) and 1 phase clock. At a distance of 500 km, accuracy obtained on frequencies of ≈43 MHz (λ ≈ 7 m) was 100-200 m.
  • Stations (p. 9-11 in ref. 164B). Transmitters built by LMT in France (with 50 W (?) and 5 kW PA stages built by SADIR in France). Station in France at Boulogne and Cherbourg (#2) cancelled ? Training stations to be comleted by end of 1943 near Vienna and Ischemberg/Munich.
  • Dora: ca. 1940, shortwave, 2 pairs of vertical dipoles in crossed configuration, with a vertical antenna at the center, rotating dual cardioid pattern; not satisfactory. 1.5 kW beacon; tool, only used for calibrating Erika. Ref. 2C4, p. 123.
  • Truhe, VHF hyperbolic pulse system, compatible with the British "Gee" system (where "Gee" stands for the letter "G" in "Grid"), which was referred to as "Hyperbel" by the Germans.
  • ref. 6G: was ultimately to cover the 20-100 MHz band and employed various types of ground transmitters including Feuerhilfe, Feuerstein, Feuerzange and Feuerland. All these transmitters could also be used to the "Gee" system. Truhe I: 46-50 MHz, Truhe II: 30-60 MHz.
  • Locations per ref. 6: A chain of Truhe stations was built around Berlin, primarily for training purposes and there were in addition groups of ground stations in the Schwarzwald and in Pomerania. The last named was intended for operations against Russia and it is not known if the stations were destroyed before their capture.
  • Airborne sets: FuGe 122 (46-50 MHz), and FuGe 123 (25-75 MHz). Ref. 6D, 230Q, 261AC1.
  • Schwanboje: ref. 6D, §22-2 [ = waterborne V.H.F. beacon dropped by parachute and originally used by K.G.40 for marking convoys or submarines]
  • Diskus: ref. 6D, §75.
  • Wullenwever: p. 12 in ref. 164B.

Post WW2 systems (german and other): Navaglobe (1946), Navar, Navascope, Ray-Dist, VORTAC, VOR-DME, Navarho/Navarho-H/-HH/-Rho, Radio Mesh System, MLS, SatNav, etc. : outside scope.


Below is a listing of patents related to radio direction finding, radio location, radio navigation (generally covering the early 1900s through WW2).Patent source: DEPATISnet. Patent office abbreviations: KP = Kaiserliches Patentamt (German Imperial Patent Office), RP = Reichspatentamt (Patent Office of the German Reich), DP = deutsches Patentamt (German Federal Patent Office), US = United States Patent Office, GB = The (British) Patent Office, F = Office National de la Propriété Industrielle (French patent office), AU = Dept. of Patents of the Commonwealth of Australia, NL = Nederlandsch Bureau voor den Industrieelen Eigendom (patent office of The Netherlands).

Note: in the USA and other countries, a company or business cannot apply for a patent. In such cases, the employee-inventor (i.e., the invention was made as part of the employment) has to apply for the patent (or the patent is applied for in the inventor's name), and then transfer (assign) the patent rights and ownership the employer/company. This assignment transfer is typically done during the application process. An inventor who is not obliged to assign the patent to an employer, may assign his patent (transfer of rights, not of invention) to any other party.

Patent number Patent office Applied Inventor / assignor Patent owner / assignee Title (original, non-English) Title (original English or translated) + brief summary
716134 US 1901 John Stone Stone Whicher, Browne, Judkins (trustees) --- "Method of Determining the Direction of Space Telegraph Signals" [Determination of the bearing of a transmitting radio station by means of a rotable loop antenna (or symmetricall arranged pair of verticals) with which "null" signal direction is found.]
716135 US 1901 John Stone Stone Whicher, Browne, Judkins (trustees) --- "Apparatus for Determining the Direction of Space Telegraph Signals" [Identical to Stone's 1901 US patent 716134.]
770668 US 1903 Alessandro Artom Alessandro Artom --- "Wireless Telegraphy of Transmission through Space" [Generation of a "compact cone" [directional beam] of radio waves, by means of combining 2 or more antennas, transmitting with different phases and directions.]
165546 KP 1904 Christian Hülsmeyer Christian Hülsmeyer (Huelsmeyer) "Verfahren, um entfernte metallische Gegenstände mittels elektrischer Wellen einem Beobachter zu melden" "Method for detecting distant metal objects by means of electrical waves" [This is the invention of radar!]
771819 US 1904 Lee de Forest Lee de Forest --- "Wireless Signalling Apparatus" [Improved, simplified devices for localizing direction of a radio station; rotable antenna (horizontal dipole, horizontal monopole + ground/earth, or vertical loop) + detector/coherer + telephone receiver, with or without battery.]
13170 GB 1904 Christian Hülsmeyer Christian Hülsmeyer (Huelsmeyer) --- "Hertzian-wave Projecting and Receiving Apparatus Adapted to Indicate or Give Warning on the Presence of a Metallic Body, such as a Ship or a train, in the Line of Projection of such Waves" [Expansion of his primary German 1904 radar patent 165546, with closely spaced transmitter & receiver antennas that are shielded from each other, antennas with cardanic suspension to maintain their orientation during ship roll & pitch movements, rotable directive transmit antenna (concave / parabolic reflector) with collocated spark gap, fed with high-voltage via slip rings; receive antenna could also made directive in same direction as transmitting antenna by using reflector.]
25608 GB 1904 Christian Hülsmeyer Christian Hülsmeyer (Huelsmeyer) --- "Improvement in Hertzian-wave Projecting and Receiving Apparatus for Locating the Position of Distant metal Objects" [Expansion of his 1904 British radar patent 13170, with constructional improvements to make elevation angle of the transmision antenna variable, so as to be able to find the azimuth & elevation combination with the strongest reflection from the target. This also allows determination of distance ( = range), as elevation angle is determined and antenna mounting height is know. For ship-mounted installation: mounting on fore deck is limited to 180° sweep due to ship superstructure behind it, so a 2nd transmitter / receiver on the aft deck can expand coverage to 360°.]
833034 US 1905 Lee de Forest Lee de Forest --- "Aerophore" ["radiation concentrating device" (directional transmitter such as spark gap + parabolic reflector) that is slowly rotated by a motor that also drives a "signalling wheel" disk (with dots & dash notches + contact) and a voltage generator + up-transformer + oscillator capacitor; the contact interrupts the voltage to generate high voltage pulses for a spark gap. Sends "code signals" (distinct patterns of several dots and/or dashes) in each azimuth sector. Rotating antenna: parabolic reflector + spark gap, or angled mono-pole  as described in the article "Notizen über drahtlose Telegraphie" ["Notes on wireless telegraphy"] by Ferdinand Braun in Physikalische Zeitschrift, Vol. 4, Nr. 13, 1 April 1903, p. 361-364, which includes §2 "Versuche über eine Art gerichteter Telegraphie" ["Tests with a form of directive telegraphy]).
192524 KP 1907 Otto Scheller Otto Scheller "Sender für gerichtete Strahlentelegraphie" "Antenna arrangement for directional radio transmission" [Multi-antenna systems could not be made directional with spark transmitters, as transmitter output could not be split; patent shows how to do this efficiently with undamped-wave transmitter.]
201496 KP 1907 Otto Scheller Otto Scheller "Drahtloser Kursweiser und telegraph" Wireless course indicator and telegraph. [Invention of overlapping beams with equi-signal; English translation is here.]
378186 F 1907 Alessandro Artom Alessandro Artom "Système évitant la rotation des antennes dans un poste de télégraphie sans fil dirigable et permettant en particulier de déterminer la direction d'un poste transmetteur" "System to avoid rotation of the antennas of a directional radio station and in particular enabling determination of the direction of a transmitter station." [identical to Artom's original Italian patent nr. 88766 of 11 April 1907. Invention of the goniometer, often erroneously attributed to Bellini & Tosi, who lost their case in Italian court against Arthom]
943960 US 1907 Ettore Bellini & Alessandro Tosi Ettore Bellini & Alessandro Tosi --- "System of Directed Wireless Telegraphy" [Antenna configuration with 2 perpendicularly crossing triangular loops (with open top = inverted-U with tips nearly touching), using a goniometer. ([FD = Artom's 1907 French patent 378186) to rotate the antenna system's directivity without physically rotating that system. The 2 antennas are excited by a transmitter such that their radiated fields superimpose and combine.]
11544 GB 1909 Henry Joseph Round Marconi's Wireless Telegraph Co. --- "Improvements in Apparatus for Wireless Telegraphy" [For directional receiving purposes: switched directional beams, here obtained with 2 inverted-L antennas.]
1135604 US 1912 Alexander Meissner Alexander Meissner --- "Process and Apparatus for Determining the Positon of Radiotelegraphic receivers" [Invention of stepwise-rotating-beam Radio Compass beacon. (FD: later referred to as the "Telefunken Compass"; also see equivalent Telefunken's 1912 Dutch patent 981).]
1162830 US 1912 Georg von Arco & Alexander Meissner Telefunken GmbH --- "System for signalling wireless telegraphy under the quenched-spark method" [Improved transmission scheme, with loose coupling between tuned antenna and spark generating circuitry, such that the continous sequence of generated spark oscillations is in sync with the oscillations in the antenna, such that they do not (partially) extinguish one another and a nearly undamped wave results.]
1051744 US 1914 Alexander Meissner Telefunken GmbH --- "Spark gap for impulse excitation" [Pair of round spark-gap plates, one with multiple round dimples (or concentric grooves), the other with mating bumps (or concentric ridges).]
981 NL 1912 - Telefunken GmbH "Inrichting voor het bepalen van de plaats van ontvangers (schepen) door middel van draadloze telegrafie" "Arrangement for position determination of receivers (ships) by means of wireless telegraphy" [Equivalent of Meissner's 1912 German patent 1135604.]
299753 RP 1916 Otto Scheller C. Lorenz A.G. "Drahtloser Kursweiser und Telegraph" "Wireless direction pointer and telegraph" [Expanding his 1907 patent with a radio goniometer to couple transmitter to antenna pair; English translation of the patent claims is here.]
328274 RP 1917 Leo Pungs Leo Pungs "Verfahren zur Feststellung der Richtung eines Empfangortes zu einer Sendestation, von der gerichtete Zeichen ausgehen" "Process for determining the direction of a receiving station relative to a transmitting station that is sending directional signals" [Accuracy of bearing determination with stopwatch of rotating-null beacons that transmit north/south signal (such as Meissner/Telefunken Kompass) depends on synchonicity between beacon & stopwatch. Invention proposes stopwatch with compass degree-scale, two hands/needles, both started simultaneously, one stopped upon reception of first null/minimum, the other upon receipt of second null. In ideal case, angle between the 2 pointers is always 180°. A second, rotable scale is aligned with first pointer and value at second pointer shows bearing correction factor if angle when angle is not 180°.]
130490 GB 1918 Frank Adcock Reginald Eaton Ellis --- "Improvement in Means for Determining the Direction of a Distant Source of Elector-Magnetic Radiation" [Receive only; 2 pairs of vertical dipoles, dipoles of each pair connected with a feedline taht includes 180° twist, in order to suppress received horizontally polarized signals. (FD: this patent is sometimes erroneously attributed to R.E. Ellis, who is actually only the assignee who acted as intermediary / patent agent in the patent application, as the inventor / assignor was serving military duty in WW1 France at that time).]
1301473 US 1919 Guglielmo Marconi, Charles Samuel Franklin Marconi's Wireless Telegraph Co. Ltd. --- "Improvements in reflectors for use in wireless telegraphy and telephony" [For receiving & transmission antenna systems; several reflector configurations, comprising screens of parallel rods, strips, or wires. arranged on a parabolic surface; FD: same as marconi/Franklin's 1919 Australian patent nr. 10922.]
328279 RP 1919 Hans Harbich & Leo Pungs Hans Harbich & Leo Pungs "Schaltung für die Richtungstelegraphie mit Vielfachantennen" "Circuit for directional telegraphy with multi-element antennas" [Antenna ranngement (many crossing dipoles connected to taps on a cylindrical coil winding, with a coaxial rotable second cylindrical coil) usable for transmission and reception; instead of rotating contactor/distributor (subject to contact wear & generating noise during reception) or goniometer (small imbalances cause large large phase shift / detuning, hence requiring very loose coupling), instead proposes tightly coupled transformer coupling with single-point-of-tuning for complete transmitter/antenna system.]
198522 GB 1922 James Robinson & Horace Leslie Crowther & Walter Howley Derriman James Robinson & Horace Leslie Crowther & Walter Howley Derriman --- "Improvements in or relating to Wireless Apparatus" [one or more symmetrical pairs of vertical antennas and feedlines, suppression of transmissioin of horizontally polarized signals of each antenna pair by crossing-over of the feedline at the mid-point between paired antenna. (FD: this is the transmission equivalent of the Adcock's 1918 GB patent 130490]
1653859 US 1923 Ludwig Kühn Dr. Erich Huth G.m.b.H. --- "Apparatus for influencing alternating currents" [Method for AM modulating a continuous RF carrier signal with of iron-core choking coils (several configurations), whose self-inductance is varied with the tone or speech audio signal current.]
252263 GB 1924 Alexander Watson Watt Alexander Watson Watt --- "Improvements in and relating to Radio-telegraphy Direction Finding and other purposes" [Adds CRT display to Adcock's DF antenna system arrangement of GB patent 130490]
475293 RP 1926 Hidetsugu Yagi Hidetsugu Yagi "Einrichtung zum Richtsenden oder Richtempfangen" "Arrangement for directional transmission or reception" [Invention of the "Yagi" / "Yagi-Uda" beam antenna; vertical monopole + ≥1 reflector (≥λ) + ≥1 director (≤½λ), spaced ¼λ); German version of the original 1925 Japanese patent nr. 69115; also see ref. 229H]
1860123 US 1926 Hidetsugu Yagi Radio Corp. of America (RCA) --- "Variable directional electric wave generating device" [Placing a vertical (passive) conductor or antenna at some distance of a likewise vertical main (but energized) antenna, and that passive conductor is resonant at a frequency lower than that main attenna (i.e., is at least ½λ long), then the conductor will reflect the waves of that antenna (project them away), and shape the radiation pattern of that antenna in a directive manner accordingly. Conversely, a conductor with a higher resonant frequency than the main antenna (i.e., is shorter than ½λ) will direct the waves of that antenna in the directions of that conductor. Patent refers to it as a beam antenna. Illustrated with several circular configurations of multiple conductors; also see ref. 229H]
481703 RP 1927 Dr. Max Dieckmann, Dipl.-Ing. Rudolf Hell Dr. Max Dieckmann, Dipl.-Ing. Rudolf Hell Funkentelegraphische Peileinrichtung Direction-finding system for spark transmitter stations [RDF system with stationary loop and a reference antenna, fast switching between antennas, galvanometer "on course" instrument]. Follow-up patent 482281, also 1927, uses pair of switching valves instead of motorized inductive coupler.
1741282 US 1927 Henri Busignies Henri Busignies --- "Radio Direction Finder, Hertian Compass, and the Like" [D/F receive; 2 perpendicularly crossing loops (each with a signal amplifier) + 2-coil galvanometer needle instrument that points at compass scale with 0/90/180/270° ambiguity; ambiguity resolved by slightly rotating the loop's pattern with a servo-driven capacitive goniometer; third config, also to eliminate ambiguity, with separate vertical omni antenna, to yield rotable cardioid pattern).]
632304 F 1927 Alexandre Koulikoff & Constantin Chilkowsky Alexandre Koulikoff & Constantin Chilkowsky "Procédé et dispositifs pour le mesure des distances au moyen d'ondes electro-magnétiques" "Method and apparatus for the measurement of distances by the use of electromagnetic waves" [invention of the radio responder / transponder and distance / range measurement obtained therewith; two receiver / transmitter stations, one initates transmission of a (pulse?) signal. Upon receipt, the second station automatically also transmits a (pulse?) signal (at the same or different frequency). Upon receipt by the first station, the latter automatically again transmits a signal, etc. The resulting back & forth transmissions have a modulation with a beat frequency that is proportional to the distance between the stations. Conversely, in absence of significant time delay between reception and tranmissions, the distance is equal to the speed of light divided by twice the beat-frequency; identical to the1928 GB patent nr. 288233 of the same inventors]
305250 GB 1927 Alexander Watson Watt & Labouchere Hillyer Bainbridge-Bell Alexander Watson Watt & Labouchere Hillyer Bainbridge-Bell --- "Improvements in and relating to Apparatus adapted for use in Radio-telegraphic Direction Finding and for similar purposes" [Expansion of their 1924 GB patent 252263; adds omnidirectional / non-directional sense antenna.]
1937876 US 1928 Eugene S. Donovan Ford Motor Company --- "Radio beacon" [A/N beacon, 2 orthogonal crossing triangular loop antennas (one "A", the other "N"; top/tip grounded, goniometer for rotating combined pattern, remote control, separate low-power transmitter + vertical omni-directional cage antenna for alternating "station indicator" (omni overfly-marker beacon; also to be installed separately along airway) or telegraphy message broadcast; equisignal beam width of 6 miles at 200 miles range (i.e., 1.2°) based on experiments; no specific modulation tone implied]
1831011 US 1928 Frederick A. Kolster Federal Telegraph Co. (part of ITT in 1928) --- "Radio beacon system" [upward beam with hollow conical radiation pattern, in-ground antenna + parabolic reflector; related US patents: 1820004 (1928, Geoffrey G. Kreusi "Aerial navigation system and method"), 1872975 (1928, Frederick A. Kolster "Navigation system and method"), 1944563 (1931, Geoffrey G. Kreusi "Directional radio beam system")]
529891 RP 1928 Alexander Meissner Telefunken GmbH "Verfahren zur drahtlosen Richtungsbestimmung" "Method for wireless determination of direction" [Improvement of Compass with stopwatch, results depend on stopwatch operator and relatively low speed of beacon rotation, hence, requires time-consuming repeated measurements and averageing. Patent: automatic, replace stopwatch with an optical indicator that (somehow...) rotates synchronously with beacon, light pulses light up at 2 spots on compass scale, based on reception of pulses from beacon beam rotating at 10-20 rps (!!!)]
502562 RP 1929 Ernst Kramar & Felix Gerth C.Lorenz A.G. "Verfahren zum Tasten von Richtsendern für rotierende Richtstrahlen" "Method for keying directional transmitters for rotating directional beams" [Using two iron-core choking coils (per Kühn's 1923 German patent 165385, but switching between 0 & 100% saturation, instead of analog modulation) for alternatingly connecting two antennas to a transmitter without using contact-switches or relays]
1941585 US 1930 Eugene Sibley Eugene Sibley --- "Radio beacon system" [A/N beacon with two orthogonally-crosssing rectangular loop antennas, separate synchronized "A" and "N" transmitters. However, not interlcoking A & N Morse characters (and "T" equisignal), but 5-bit Baudot-type encoding of A & N (11000 and 00110 respectively) and K (11110) equisignal. Combined with a "Teletype" keyboard teleprinter system for transmitting the (adjustable) beacon course to the pilot via the beacon's directional loop antennas, or course, weather and other broadcast info, via the non-directional marker of the beacon station or en-route marker beacons. Automatic compact "Teletype" tape printing telegraph in the cockpit. Demonstrated.]
546000 RP 1930 Meint Harms Meint Harms "Verfahren einer selbsttätigen Ortsbestimmung beweglicher Empfänger" "Method for position finding by a mobile receiver" [Invention of hyperbolic radio navigation; autonomous localization of a moving receiver by using 2 (or more) coherent CW transmitter stations with spacing equal to integer multiple of the wavelength. One station acts as master, with stable phase, the second is synchronized to it and transmits on 2x the Master frequency (or, in general, any frequency that is coherent with the Master's) without phase shift. Receiver has 2 antennas, one for the Master frequency, the other for the Slave frequency. The receiver amplifies both signals separately, while at the same time doubling (or whatever the coherent Amster-Slave frequency factor is) the frequency of the Master's CW signal. The 2 resulting same-frequency CW signals are combined/compared, and the result drives an electro-mechanical up/down counter. Starting at a know position, each time movement causes Master-Slave phase difference to make a 360° → 0° transition, the counter value is changed in one direction, and in the opposite direction upon each 0° → -360° transition. So, during movent along a 0° phase difference hyperbel, the counter vale is not changed (FD: i.e., counter value change corresponds to 1λ hyperbel change).]
363617 GB 1930 Reginald Leslie Smith-Rose & Horace August Thomas Reginald Leslie Smith-Rose & Horace August Thomas --- "Improvements in or relating to Wireless Beacon Transmitters"  [Rotating beacon, 6-10 ft square loop antenna, rotating about a vertical axis at 1 rpm; transmitting a characteristic signal when passing the geographical meridan [ = north/south direction], receiver uses stopwatch to measure time between passage of reference signal and signal's minimum-intensity passage; vertical loop or inclined loop with suppression of non-horizontal radiation; also covers version comprising 2 pairs of vertical antennas with a goniometer with 1 stator and 2 rotors.]
661431 RP 1930 Ernst Kramar C. Lorenz A.G. "Einrichtung zur Richtungsbestimmung drahtloser Sender" "Arrangement for direction finding of wireless transmitters" [Apparent width/sharpness of "A/N" (or similarly complementary keyed) equisignal beam, depends on accuracy of the A/N signal-strength comparing electronic instrumentation that is used for determining course deviation, esp. for visual indicator. Constant two-tone instead of A/N keying system requires accurate tone filtereing and high signal strength and/or high-gain reed-instrumentation. Significant improvement of sensitivity / apparent beam-sharpness by using (diode tube) rectifiers with quadratic characteristic, to increase the apparent relative signal strength of the received 2-tones.]
2014732 US 1930 Clarence W. Hansell Radio Corporation of America (RCA) --- "Radio beacon system" [3 crossing rectangular loop antennas (or 3 vertical antennas on corners of triangular footprint) + 1 vertical omni-directional antenna at center; cardiod pattern; transmitter = crystal controlled carrier-frequency generator + modulator + "modulating wheel" tone generator driven by synchronous motor (continuously variable pitch = FM modulation with tone "chirp": 2 Hz sawtooth signal with 150-250 Hz linear tone ramp) + 4 amplifiers (1 for each of 3 loops/verticals, 1 for central vertical omni antenna). Synchronous 2 rpm motor also drives goniometer to continuously rotate the cardiod pattern. Receiver audio output is fed to a circular indicator with 36 reeds, each tuned to a tone in the 150-250 Hz range. Patent claims system was actually demonstrated.]
349977 GB 1930 John M. Furnival, William F. Bubb Marconi's Wireless Telegraph Co. Ltd. --- "Radio beacon" [2 orthogonal crossing triangular loop antennas + goniometer; cam-driven callsign/identifier Morse code; standard 2 or more adjustable equisignal directional zones (e.g., cam-driven A/N system), and rotating directional signal/beam (cardioid or figure-of-8 using same 2 loop antennas) with predetermined speed + omni-directional reference direction marker (e.g., north passage ID), i.e., the 1912 Telefunken/Meißner system per German patent 1135604]; same as the Furnival/Bubb US patent 2045904 filed a year later (in 1931), which has, however, Radio Corporation of America (RCA, originally Marconi's Wireless Telegraph Co. of America, "American Marconi") as assignee/owner.
1945952 US 1930 Alexander McLean Nicolson Communications Patents, Inc. --- "Radio Range Finder" [One of the stations initiates an RF carrier impulse of predetermined duration (e.g., 10-100 cycles of a 1 MHz carrier). The receiver of the second station (referred to as "reflecting" station) keys the associated transmitter for the duration of the received pulse. The resulting is received back at the initiating station, after round-trip travel time at the speed of light. That time is proportional to twice the distance between the stations. Like the second station, the receiver in the initiating station now keys the associated transmitter for the duration of the received pulse. This results in continuous back-and-forth transmissions. The resulting beat-frequency indicated on a meter instrument with distance scale. (FD: this method is a copy of the one in the 1927 Koulikoff & Chilkowsky responder/transponder patents FR632304 and GB288233!) In a second embodiment of the method, a manually variable re-transmission delay is used in the originating station is used, which is adjusted until the circulating beat frequency is zero. Patent claims that meter or audible tone may also indicate direction of travel. However, it can only do so in the sense of increasing or decreasing distance (i..e, not bearing)! ]
1949256 US 1931 Ernst Kramar C. Lorenz A.G. --- "Radio Direction Finder" [Visual course-deviation indicator/meter with dial/scale, for use with an equi-signal beam fixed course-beacon (e.g., A/N, or easier to interpret by pilot: E/T = dot/dash). Four embodiments (circuit diagrams) shown, all transformer-coupled audio output of receiver, a rectifier (tube/valve) with quadratic characteristic (to obtain high gain for small differences), and a galvanometer. The meter-needle swings about the non-zero deflection corresponding to the equi-signal, in the rhythm of the received dots & dashes, and the swing amount depends on the relative strength ( = course deviation direction and amount). Note: this is not a "kicking meter" arrangement, in which dot/dash pulses are passed through an inductive differentiating circuit, and meter deflection is about the zero indication. Also proposes transmitter keying not with square pulses, but rounded pulses with "rapid rise"/"slow decay" pulse flanks for one of the two overlapping beams, and the opposite for the complementary beam.]
1923934 US 1931 Frank G. Kear US Government --- "Radio beacon course shifting method" [shift 2 beacon courses from their normal 180° displacement to align them with 2 airways that intersect at an angle other than 180°; expand 2-loop/2-pair antenna config with separate vertical antenna (inductively coupled to one of the goniometer primaries) whose omni-directional patternn combines with the figure-8 of 1 loop to create a cardioid.]
1992197 US 1932 Harry Diamond US Government --- "Method and apparatus for a multiple course radiobeacon" [rapid increase in number of airways emanating from major airports means need beacon capable of marking > 4 courses; 3-tone beacon with up to 12 simultaneous courses; 2 triangular vertical loops crossing at 90°, several transmitter configurations (transmitter with master oscillator (carrier freq) + 3 intermediate modulator-amplifiers (65, 86⅔, 108⅓ Hz tones) + 3 final amplifiers, special goniometer with 3 stators (1 for each PA, spaced 120°) + 1 rotor (2 coils crosssing at 90°, each coil 3 sections); several other transmitter configurations.]
1913918 US 1932 Harry Diamond & Frank G. Kear US Government --- "Triple modulation directive radio beacon system" [expansion of H. Diamond triple-modulation/12-course beacon system 1932 US patent 1992197, same diagrams, adding method for shifting the normally 30°-spaced individual courses of the 12-course beacon, to align them to the airways.]
577350 RP 1932 Ernst Kramar C. Lorenz A.G. "Sendeanordnung zur Erzielung von Kurslinien" "Transmission arrangement for creation of course lines" [This is the invention of what was later called the "Lorenz Beam", localizer part of the Instrument Landing system; create equisignal beam, not with two separate directional antenna systems with overlapping patterns, but with a single omnidirectional vertical dipole antenna whose continuously active circular pattern is alternatingly deformed into a bean-shaped pattern to the left and right, by activating a corresponding parallel vertical reflector ( = passive) that is placed at some distance to the right & left of the vertical antenna. The two reflectors are alternatingly enabled in the standard A/N or similiar dots/dashes rhythm. The shape of the "bean" patterns depends on the length of the reflector rods and the distance between the reflectors and the dipole antenna. This method also eliminates key-clicks, since the vertical dipole is allways energized (i.e., not keyed).]
592185 RP 1932 Ernst Kramar & Felix Gerth C. Lorenz A.G. "Gleitwegbake zür Führung von Flugzeugen bei der Landung" "Glide path beacon for guiding airplanes to landing" [Blind/fog landing requires localizer/course beam and glide-path guidance. The latter follows the curved constant-field-strength path upon beam intercept. So far, ground stations used a LW localizer beam and separate VHF glide path beacon. This requires two complete beacon transmitter and receiver systems. Patent proposes simplification by using a single VHF equisignal beam beacon system with complementary keying (with choking-coils; FD: see Kühn's 1923 US patent 1653859 and Karmar/Gerth's 1929 German patent 502562) with asymmetrical pulses (short-rise/long-fall times for one beam and the opposite for the other beam; here: triangular pulses (FD: Kramar's patent 1949256 proposes rounded pulses). The VHF receiver's audio output is rectified. The rectifier output is fed to a galvanometer that indicates the combined/summed strength of the two beams, and is used to fly a constant-strength curved glid path. The rectifier output is also transformer-coupled to a push-pull amplifier stage that drives a kicking-meter (alternatively, the rectifier output can feed a differential-galvanometer). This meter indicates course deviation.]
405727 BP 1932 --- C. Lorenz A.G. --- "Directional radio transmitting arrangements particularly for use with ultra-short waves " [Same as Lorenz' 1932 German patent 577350]
589149 RP 1932 --- C. Lorenz A.G. "Leitverfahren für Flugzeuge mittels kurzen Wellen, insbesondere ultrakurzer Wellen" "Method for guiding aircraft by means of short waves, in particular ultra-short waves" [Landing beacon arrangements to accommodate final descent to a landing from various heights, in particular steep descents from higher altitudes, and glide path intercept (FD: from below = the way it shoud be done) from greater distance. One arrangement with standard Lorenz course beacon ( = vertical dipole + 2x reflector) placed at the approach end (!!!!) of the runway (serving as course beacon and runway marker beacon), and a standard equisignal glide path beacon placed at the departure end (!!!) of the runway. By using different modulation tones, both could operate on the same frequency (in particular with appropriate tone filters at the receiver). Other arrangement with two co-located standard Lorenz course beacons side-by-side, the plane of the antenna systems of these beacons at an appropriate elevation angle instead of vertically (to generate glide path beam of 8-11° (FD: vs. 3° standard in modern times), and at an angle with respect to each other such that their equisignal beams cross; slightly expanded by Lorenz' same-title 1933 German patent 607237.]
1961206 US 1932 Harry Diamond US Government --- "Twelve-course, aural type, triple modulation directive beacon" [Explicitly aural beacon ( = requires interpretation of 3 audio tones (e.g., 850, 1150, 1450 Hz) by pilot, i.e., not 12-course VISUAL beacon with visual instrument to interpret the tones; Aural 12-course beacon were considered impossible, as for 6 of the 12 courses, the 2 overlapping tones that form the equi-beam are overpowered a much stronger figure-8 lobe of the 3rd tone; LW (e.g., 290 kHz) transmitter blockdiagram for 2 configs; keying device between modulators with slip contacts on rotating cylinders with patterns of conductive patches)pilot selectable audio filters.]
2093885 US 1932 Ernst Kramar & Felix Gerth Standard Elektrik Lorenz A.G. --- "Means for guiding aeroplanes by radio signals"  [Two overlapping VHF beams for lateral guidance, curved glidepath on constant signal strength of same 2 beams; FD: equivalent to Lorenz' 1932 German patent 592185.]
408321 BP 1932 --- C. Lorenz A.G. --- "Radio beacon for directing aircraft" [Two overlapping VHF beams for lateral guidance, curved glidepath on constant signal strength of same 2 beams; FD: equivalent to Lorenz' 1932 German patent 592185.]
2028510 US 1932 Ernst Kramar C. Lorenz A.G. --- "Transmitter for electromagnetic waves" [FD: equivalent to the 1932 German "Lorenz Beam" patent 577350.]
1981884 US 1933 Albert H. Taylor, Leo C. Young, Lawrence A. Hyland Albert H. Taylor, Leo C. Young, Lawrence A. Hyland --- "System for detecting objects by radio" [Detection of moving objects (e.g., aircraft, ship, motive vehicle), system comprising CW transmitter and remotely located receiver, continuously receiving ground waves directly from transmitter (constant signal), and intermittently receiving skywaves that are not reflected (!!!) but re-radiated by such conductive/metallic objects (or parts thereof) that have a size of ca. ½λ of the transmitted CW signal, and that interfere/combine with the ground waves signals (causing variable amplitude at receiver). Amplitude of the interence pattern signal fluctuates when object moves, more rapidly (and with larger amplitude) when moving over receiver or transmitter site. Also, moving parts of the object (e.g., rotating propeller(s) = "propeller effect"), cause superimposed distinguishable modulation of the interence pattern signal. Ground wave may be extinguished by the time it reaches receiver, or be transmitted in dirction of receiver if using directional transmitter.]
2121024 US 1933 Harry Diamond US Government --- "Radio transmitting and receiving system" [System for simultaneous transmission of radiotelephone (e.g., broadcast of weather & landing conditions) and radio range beacon signals. For some time, these 2 radio services used different radio frequencies; due to expansion of beacon network, frqeuencies becoming scarce. Method for simultaneous transmission, without overlapping modulations. 2 loop antennas for beacon service, separate omni antenna for broadcast service; single master RF oscillator for both services, with 3+1 intermediate modulator amplifiers (3 keyed tones + microphone or recorded message), and 3+1 final amplifiers; 2-outputs tone filter unit between receiver and headphones, with LPF for beacon signals and HPF for broadcast audio.]
2172365 US 1933 Harry Diamond US Government --- "Directive antenna system" [Radio range beacon; to eliminate erroneous course indications with crossing loop beacons due to "night effect", now antenna configuration with 2 pairs of 2 vertical antennas, evenly spaced, each with ground plane, all with same feedline distance to transmitter, coupled to a single transmitter via a radio goniometer and tuned feedlines to a coupling transformer for each antenna pair, with 180° twisted feedline between on the antenna side of these transformers. Refers to patents GB130490 (1919), GB198522 (1923), and GB363617 (1932).]
1999047 US 1933 Walter Max Hahnemann C. Lorenz A.G. --- "System for landing aircraft" [Upon intercept, as indicated on meter, the pilot adjusts vertical flight path as necessary, such that the meter deflection does not change from the indication at moment of intercept (absolute deflection is not important). Various converging curves can be selected ( = steepness), by adjusting the receiver/indicator gain, also possible a receiver device that is triggered by reception of the marker beacon and with a timer, moves the indicator scale to indicate estimated height above ground.]
2348730 US 1933 Francis W. Dunmore & Frank G. Kear US Government --- "Visual type radio beacon" [Fixed course beacon comprising 2 pairs of "transmission line" (TL) antennas (pair of vertical monopoles with ground planes, instead of 2 crossing loops) with figure-8 pattern (90° phase shifted excitation), with a different modulation tone (65 & 83⅔ Hz) for each pair (feed-line arrangement to eliminate "night effect"), combined with two co-located omni-directional transmissions on same frequency but with 270° phase difference, with the same 2 modulation tones; combined "figure-8 and omni" pattern pairs form cardioid pattern; two 2 overlapping cardioids form 2 equisignal course lines; refers to description in CAA-ACM 1932 No. 2.]
653519 RP 1933 --- Marconi's Wireless Telegraphy Co. Ltd. "Verfahren zur Übermittlung von Nachrichten allert Art auf drahtlosem Wege" "Method for wireless transmission of messages" [directly readable, omni-directional transmission of, e.g., weather data, as pointer on CRT display with scale, without synchronization complexity of TV or fax]
2072267 US 1933 Ernst Kramar C. Lorenz A.G. --- "System for Landing Aircraft" [Expanded by 1937 follow-up Lorenz' 1937 US patent 2215786 "System for landing airplanes".]
2120241 US 1933 Harry Diamond & Francis W. Dunmore US Government --- "Radio guidance of aircraft" [UHF landing/take-off beam beacon, method and apparatus, able to serve all wind directions with a single beacon that has variable glide path steepness to a proper/predefine touch-down point. Demonstrated at College Park/MD and Oakland/CA airports. Beacon antenna placed in a pit, just below ground level of the airfield / landing zone. First antenna arrangement: horizontal UHF dipole. With this installation position, the dipole's torus radiation pattern in free space (FD: i.e., figure-8-on-its-side vertical cross-section in all directions) is pushed upward with increasing distance from the antenna, enabling curved constant-field-strength glide path. The horizontal dipole can be made rotable about its vertical axis (with remote controlled motor and 2 slip rings to feed the antenna) to accomodate any pair of 180° spaced directions (2-course). A rotable 4-course equivalent can be obtained by using two crossing dipoles with 2 pairs of slip rings.]
2044852 US 1933 Ernst Kramar C. Lorenz A.G. --- "Electric indicator for comparing field intensities" [E/T equisignal beam deviation indicator; standard circuitry with rectifier and transformer; galvanometer. References 1928 US patent 1782588 "Electrical mesasuring instrument" (2-pole galvanometer with rotary coil) by F.E. Terman. The desrired meter sensitivity reduction for increasing meter / needle deflection is obtained electromechanically instead of electronically, by tapered (instead of concave) shape of the galvanometer poles.]
616026 RP 1934 --- C. Lorenz A.G. "Sendeanordnung zur Erzielung von Kurslinien gemäß Patent 577 350" "Transmission arrangement for obtaining course-lines per Lorenz' 1932 German "Lorenz beam" patent 577350" [vertical dipole + two near-resonant reflectors]
612825 RP 1934 --- C. Lorenz A.G. "Verfahren zum Betrieb von Funkbaken" "Method for operating a radio beacon" [2-course A/N or E/T beam; left/right beams are swapped, based on which of the two courses is actively used by aircraft, such that indicated left/right course deviation indications is correct for both, i.e., A & N (E & T) always on the same side of the equisignal beam when approaching the beacon]
2196674 US 1934 Ernst Kramar & Walter Max Hahnemann C. Lorenz A.G. --- "Method for Landing Aircraft" [Localizer beacons that are used to provide guidance for curved, constant field-strength approach to landing, typ. depend on constant transmitter power and constant receiver gain (FD: at least during the beam intercept and final approach & landing phase). The latter is more difficult to ensure than the prior. Method usable with equisignal course beam beacons, elevated/upwardly transmitted radiation patterns, and torus-shaped patterns (FD: e.g., from a vertical dipole or monopole). Method uses a marker beacon (accoustic or - preferred - radio) below the intended point of positive intercept of the desired constant field-strength curves. This also supports using the same curve, even if intercepting at a different altitude. Aircraft to approach & intercept the beam (FD: from below) at a predermined altitude. The marker beacon may transmit vertically or at some other, steep elevation angle in te direction of the approach. Upon intercept, as indicated on meter, the pilot changes vertical flight path such that the meter deflection does not change from the indication at moment of intercept (absolute deflection is not important). Various converging curves can be selected ( = steepness) with method covered by Hahnemann/Lorenz' 1933 US patent 1999047. Patent also references Kramar/Lorenz' 1932 US "Lorenz Beam" patent 2028510]
2217404 US 1934 Walter Max Hahnemann & Ernst Kramar C. Lorenz A.G. --- "System and Method for Landing Airplanes" [Expansion of Hahnemann/Kramar 1934 US patent 2196674 with the manually adjusted receiver/indicator configurations per Fig. 4 & 5 of Hahnemann's 1933 US patent 1999074]
2025212 US 1934 Ernst Kramar C. Lorenz A.G. --- "Radio Transmitting Arrangement for Determining Bearings" ["Lorenz Beam" beacon station with continously rotating equisignal beam course direction. Standard antenna arrangement (continously excited vertical dipole (with omni pattern), a vertical reflector on each side, motorized A/N keying for complementary reflector interruption). However, now with the reflectors continously rotating about the vertical dipole, with the relays used to interrupt each reflector controlled via slip rings, to create a rotating 2-course equisignal beam system. This is much simpler than an arrangement with a motorized radio goniometer. During passage of the equisignal beam pair through a predetermined bearing (e.g., north/south), the interruption of the reflectors is briefly stopped and a predetermined combination of Morse characters is omni-dirctionally transmitted via the vertical dipole (keying by hand or motorized). receiver station determines bearing to/from station based on timing beam passage after "north" signal (FD: = Telefunken Compass stopwatch method). Alternatively, a short special character (e.g., a single dot) could be tranmsitted omnidirectionally at regular bearing increments (e.g., every 5°), and the receiver's bearing be estimated simply by counting the number of received dots since the north/south signal reception]
2083242 US 1935 Wilhelm Runge Wilhelm Runge --- "Method of Direction Finding" [3D RDF method, searching direction with maximum signal strength (unlike minimum method, accuracy is not affected by background noise, static, etc.) with a highly directional antenna system; antenna beam is moved, such that its narrow/sharp beam is precessed (conical movement) about a pointing direction (without changing the polarization direction of the antenna). Beam precession is obtained either mechanically (precession manually or with motor drive, and receiving dipole with a parabolic reflector, on a platform with manual or motorized rotation about vertical axis to change bearing, manual elevation axis adjustment; adjustments until strength of received signal remains constant (FD: this is referred to as "hill climbing" technique in modern control systems engineering terminology), or electrically (a stationary "flat" symmetrical 2D array of dipoles, with beam sweeping by means of changing phases (feed line lengths) between the dipoles.]
2184843 US 1935 Ernst Kramar C. Lorenz A.G. --- "Method and Means for determining Position by Radio Beacons" [Method of determining bearing at the receiving station, automation of this method, for use with rotating equisignal beam beacon with 1) E/T keying (60 per 360° rev of the beacon = 15 per quadrant = 1 per 6° rotation), 2) omni-directional transmission of sync/timing/zero signal upon beam passage through specific direction (e.g., north), and 3) beam transmission only during the first 180° rotation after the sync signal; standard "kicking meter" differentiating circuitry (transformer) for converting leading & trailing edge of received E & T tone pulses into short voltage peak pairs (polarity sequence +/- for E, -/+ for T); these + & - peaks are counted separately with 2 electro-mechanical counting devices; stopwatch-type bearing indicator that is reset & started manually or automatically based on receipt of the omni "north" signal) and stopped automatically by the counters upon detection of the equibeam signal; bearing ( = angle from the sync signal) is difference in number "a" of dots and number "b" of dashes reecived between the sync signal and equisignal beam passage, multiplied by half the number "f" of dots & dashes per 360°, i.e., (a-b)*(f/2).]
180995 CH 1935 --- C. Lorenz A.G. "Sendeanordnung zur Erzielung von Kurslinien mittels zweier verschieden gerichteter, abwechselnd asugesandter Hochfrequenzstrahlungen" "Transmission arrangement for generating course lines bei means of two high frequency fields, alternatingly sent in two different directions"  [standard Lorenz landing beam beacon = vertical dipole + 2 alternatingly switched parallel passive reflectors, E/T = Dot/Dash keying]
180996 CH 1935 --- C. Lorenz A.G. "Verfahren zum Betriebe von Funkbaken" "Process for operating radio beacons" [standard Lorenz landing beam beacon = vertical dipole + 2 alternatingly switched parallel passive reflectors, E/T = Dot/Dash keying, but two sets of outer & inner marker beacons (on front course & back course); to avoid confusion interpreting inverted left/right meter deflection on front course vs backcourse, keying of the reflectors can be inversed, depending on which equisignal course the inbound aircraft is using.]
44879 F 1935 --- C. Lorenz A.G. "Appareil transmetteur pour les ondes électriques et en particulier pour les ondes ultra-courtes" "Transmitter for electrical waves, in particular ultra-short" [A vertical dipole at an appropriate height above ground has a radiation pattern that resembles a torus (ring) that is slightly angled upward, away from the antenna (as opposed to a perfect torus when in free-space), instead of a perfect torus if that dipole were in free space. Likewise, if the dipole pattern is deformed with a vertical deflector. Thus upward angle makes it possible for the same beacon to provide glide path guidance. Localizer beacon placed at standard position (on the landing course-line, beyond departure end, and outside the boundary of the airfield (FD: in those days, airfields were often round, without runways). Lines of constant equisignal field-strength emanate from the beacons antenna system, curve downwards towards ground level over some distance, then curve upward with increasing distance. No radiation straight up (FD: i.e., the "hole" in the torus). Pilot follows equisignal localizer beam inbound at the certain altitude, until intercepting a particular curved constant-strength line (or receiving the signal from a marker beacon placed on the course line), and then descends to landing, ensuring that the indicated signal strength remains constant, i.e., the aircraft follows the associated curved line (glide path). Similar to Kramar/Hahnemann's 1934 US patent 2196674.]
2134535 US 1936 Wilhelm Runge Telefunken GmbH --- "Distance Determining System" [Based on received signal-strength. Method depends on receiver sensitivity and transmitter power. Distance is derived from signal strengths received by 2 antennas installed at the same location but a different heights above ground/sea. In general at VHF and horizontally polarized waves, received field intensity is zero at zero height, and changes in sinusoidal manner with increasing height, due to interference of slanted direct wave and ground-reflected wave (single "bounce"). Path-length difference between those waves is equal to 2x product of the transmitter & receiver antenna height, divided by distance over ground level. Receiver audio level is proportional to square of field strength. For known transmit & receive antenna heights + audio volume ratio of the 2 receive antennas, a formula for distance-over-ground is derived.]
2117848 US 1936 Ernst Kramar C.Lorenz A.G. --- "Direction Finding Method" [D/F antenna and circuitry arrangement to produce 2 alternating/opposed cardioid patterns. Instead of standard arrangement of two loop antennas that are alternately combined with an omni-directional antenna, or of single loop with alternatly used center tap: loop antenna + 2 omni antennas, one of which generates 2x the signal strength as the other and with opposite sign, all 3 antennas coupled to the input tube of the same receiver. The "2x" omni antenna is connected via variable coupling, to create a rotable cardioid. Same antenna is activated with switch, typ. in rythm with 50% on/off duty cycle.]
2170659 US 1936 Ernst Kramar C.Lorenz A.G. --- "Direction Finding Arrangement" [D/F antenna and circuit arrangement, with alternately connecting 2 loop antennas with opposite sense of winding (and directivity), switching controlled by a motorized commutator, aural output and visual indication to pilot/operator (the latter in the form of a signal-strengths comparing indicator per Kramar's 1933 US patent 2044852).]
2141247 US 1936 Ernst Kramar & Heinrich Brunswig C.Lorenz A.G. --- "Arrangement for Wireless Signaling" [References Kramar's 1932 US patent 2028510, which itself is equivalent to Kramars 1932 German "Lorenz Beam" patent 577350, as baseline for the antenna arrangement of 1 vertical dipole + 2 switchable reflectors (FD: resulting plane measures ca. ½λ x ½λ). The physical length of the dipole and the reflectors is reduced significantly (e.g., to 1/8 λ or 1/3 λ), and the associated reduction in electrical length is compensated by adding inductances (FD: "loading coils"). The omni-directional radiation pattern of the dipole is hardly affected by shortening the dipole, as well as by the angles of intersection between the two overlapping beams. If the electrical length of the reflectors is also reduced, and compensated back up to ¼λ or ½λ, the patterns becomes more cardioid than that of the baseline arrangement. (FD: ¼λ spacing must be retained for the reflectors to work as such). Principle of the patent is applicable to directional reception and transmission. ]
734130 RP 1937 Ernst Kramar & Walter-Max Hahnemann C.Lorenz A.G. "Ultrakurzwellen-Sendeanordnung zur Erzielung von Gleitwegflächen" "Arrangement of VHF transmission for generation of glide path planes" [Curved "constant field strength" glide path: curve to be used (FD: steepness & gradient) depends on aircraft type (approach speed, etc.). If beacon beyond departure end of runway, then beam elevation adjusted such that flat bottom of curves coincides with intended touch-down point. More optimal curve(s) obtained when curve bottom coincides with ground level at the beacon location. This requires beacon installation at the intended touch-down point. E.g., 2 UHF beacons with horizontal diople just below ground level at the intended touch-down point (FD: i.e., per Diamond/Dunmore's 1933 US patent 2120241). Straight glide path guidance can be obtained with equisignal beam, e.g., two VHF dipoles below ground (fed in-phase by common transmitter), spaced several wavelengths on the localizer course line. Also see equivalent Hahnemenn/Kramar 1939 US patent 2210664]
816120 FR 1937 Le Matériel Téléphonique S.A. Le Matériel Téléphonique S.A. "Systèmes de guidage par ondes radioélectriques par exemple pour l'atterrissage des avions sans visibilité extérieure" "Radio guidance systems, e.g., for landing aircraft without external visibility" [Antenna arrangement for creating 2 overlapping beams with equisignal zone, front-course only, no significant back-course beams (i.e., 1-course, not 2-course pattern). Hence, no ground & obstacle reflections from the back-course emissions. arrangement with vertical dipole + reflector at ¼λ + 2nd vertical dipole (or director) at ½λ + side-reflector at ¼λ, transmitter located behind the reflector (in the now suppressed back-course zone). Two such arrangements to obtain the 2 overlapping beams. Vertical (glide path) guidance via standard visual/instrument method (curve of constant field-intensity), enhanced with device that converts signal strenght to audio tone frequency, hence, deviation from constant field-strength curve changes the audio pitch.]
2147809 US 1937 Andrew Alford Mackay Radio & Telegraph Co. --- "High frequency bridge circuits and high frequency repeaters"  [transmission-line bridge to combine two tone-modulated RF signals with same carrier frequency; used on 90/150 Hz Localizer and Glide Slope systems]
705234 RP 1937 Ernst Kramar & Dietrich Erben C.Lorenz A.G. "Sendeanordnung zur Erzeugung von geknickten Kurslinien" "Arrangement for generating angled/bent course lines" [In the standard configuration of equisignal beam beacon with 1 vertical dipole + 2 alternately switched vertical reflectors (FD: i.e., "Lorenz Beam"), is with reflectros spaced symmetrically left & right of the dipole. Resulting radiation pattern has 2 equisignal beams that point in opposite directions. Beam directions can be shifted to obtain angles other than 180°/180° ((FD: this is referred to as "course bending"), by spacing the reflectors asymmetrically with respect to the dipole. Extreme case of using dipole with single reflector also has this effect, but makes equisignal beam unsharp. Alternative configuration is vertical dipole with symmetrically spaced reflectors, but reflectors of unequal length, one ½λ and the other < ½λ (FD: i.e., 1 reflector + 1 director).]
720890 RP 1937 Ernst Kramar & Werner Gerbes C.Lorenz A.G. "Anordnung zur Erzeugung einer geradlinigen Gleitwegführung für Flugzeuglandezwecke" "Arrangement for generating straight glide path guidance for aircraft landing purposes" [Curved "constant field-strength" beacon glide paths are generally (too) steep on approach and (too) flat near ground, resulting in (too) high landing speed and associated extended floating before actual touch-down. (FD: also require constant power controls and pitch angle adjustments by pilot, instead of stabilized approach, which is highly undesirable and bad practice). A (near-)straight glide path guide beam can be obtained with an upwardly angled equisignal beam (of two vertically overlapping complementary keyed beams, instead of using curves of horizontally overlapping beams). Optimal equisignal beam elevation angle is ca. 3°. High sensitivity for glide path deviation indication requires very sharp/directive sub-beams. For practical antenna system dimensions, this implies UHF radio frequencies (freq. > 300 MHz = wavelenghts < 1 mtr); multiple equisignal beams (at separate elevation angles), separated by sharp nulls, are obtained when antenna system placed several wavelengths above ground. No problem, if always intercepting the equisignal beams from below. So far, nothing new. Proposed antenna configuration: two stacked vertical collinear dipoles. A/N keying makes it possible to identify the multiple glide slope (GS) beams, as the "A" & "N" sub-beams are above/below the lowest GS beam, below/above the next (steeper) GS beam, etc. Same beam patterns can also be obtained with a single vertical antenna that is several wavelengths long (FD: to obtain pattern with multiple lobes), the electrical length of which is cyclicly momentarily slightly increased in the standard complementary keying rythm. Also see Kramar's 1938 US patent 2297228]
2215786 US 1937 Ernst Kramar & Walter Max Hahnemann C.Lorenz A.G. --- "System for landing airplanes" [Partial continuation of Kramar/Hahnemann's 1934 US patent nr. 2196674. Known is VHF beacon with upwardly-angled omni-directional torus-shaped radiation pattern, creating constant-signal-strength glide path curves. This required constant transmitter output and constant receiver gain during the landing phase. Patent proposes using one or more marker beacons, with narrrow pattern across thee approach course line, to indicate glide path intercept planes, and starting point for following constant-signal-strength glide path. (FD: no significant expansion of the referenced 1934 patent).]
2226718 US 1937 Ernst Kramar & Walter Max Hahnemann C.Lorenz A.G. --- "Method of Landing Airplanes" [Continuation of Kramar/Hahnemann's 1934 US patent nr. 2196674 and their 1937 US patent 2215786. ]
767399 RP 1937 Ernst Kramar & Joachim Goldmann C.Lorenz A.G. "Verfahren zur Erzeugung einer vertikalen Leitebene" "Method for creating a vertical guidance plane" [Method for long-range navigation; standard beacon with two complementary-keyed (e.g., A/N) overlapping beams with associated equisignal beam course-line, operating on Longwave or VHF frequencies, suitable for short-range; very long range navigation (great-circle) requires short-wave frequencies; on short-wave, radio waves propagate as groundwaves and skywaves. The latter are refracted by E &amp; F layer in ionosphere, depending on wave elevation angle and frequency. At the receiver station, these various waves combine / interfere; associated phase differences cause periodic fading and A/N distortion, affecting apparent course line. Solved with elevated directional beams (3 parallel vertical dipoles one 1 line + 2 reflectors on perpendicular line through center dipole), such that received skywave is always stronger than the groundwave. Antenna arrangement can be made azimuth-rotable. References Hahnemann's 1924 German patent 474123, Yagi's 1926 German patent 475293, and LMT Co.'s 1937 French patent 816120.]
2206463 CH 1938 --- C. Lorenz A.G. "Sendeanordnung zur Erzielung von Kurslinien" "Transmission arrangement for generating course lines" [Simplified Lorenz landing beam system; vertical dipole with single periodically activated parallel passive reflector.]
731237 RP 1938 Ernst Kramar C.Lorenz A.G. "Empfangsverfahren für Leitstrahlsender" "Method of reception of guide beam beacons" [Method for obtaining simultaneous aural & visual indication regarding equisignal beam of beacons with two overlapping-beams that are complementary-keyed with two different modulation tones. At receiver, the 2 tones are separated with 2-channel filter unit, rectified and fed to a comparing visual instrument. Beacon also broadcasts its keying signal via separate modulaton frequency. This is also received, and used to drive a commutating relay (i.e., synchronized to the beacon keying) for passing the filtered received tones to circuitry that generates their harmonics that are modulated such that the 2 complementary keyed tones now have the same audio frequency (i.e., as if the beacon was a standard 1-tone complementary-keyed one), and fed to the headphones. Also see Kramar's equivalent 1939 US patent 2255741]
206464 CH 1938 --- C. Lorenz A.G. "Rotierende Funkbake" "Rotating radio beacon" [Motorized rotating antenna arrangement of 2 pairs of vertical antennas (grounded monopoles or dipoles) at corners of a square, Adcock arrangement, simultaneously fed by transmitter via , central vertical monopole, fed simultaneously by same transmitter; creates rotating equi-signal beams; using shortwave to obtain long range]
767522 RP 1938 Ernst Kramar & Felix Gerth & Joachim Goldmann & Heinrich Brunswig C.Lorenz A.G. "Empfangsvorrichtung zur Richtungsbestimmung mittels rotierender Funkbake" "Receiving device for determining direction with a rotating radio beacon" [Rotating-beam beacon with omnidirectional north-signal pulse and rotating minimum/null; mentions optical device with synchronously rotating light bulb (inaccurate, complicated construction) and CRT display (Braunsche Röhre) showing pip upon receipt of max signal]
711673 RP 1938 Ernst Kramar C.Lorenz A.G. "Gleitweglandeverfahren" "Glide Path Landing Method" [The curved/parabolic constant-field-strength VHF glide paths are too steep at altitude and too flat near ground (with high engine power setting, resulting in floating down the runway due to high speed), which cannot be done with all aircraft type. Beam method provides (near-)straight glide path (FD: i.e., glide slope), allowing descent to landing with constant descent rate ( = constant vertical speed), and round-out (UK) / flare (US) with idle engine(s). This is achieved with a beacon that has a heart-shaped horizontal radiation pattern (heart-tip at the antenna system), angled towards the inbound approach direction (line hearth-tip / heart-dip crossing the approach track outside the airfield perimeter). Radiation pattern obtained with 2 vertical antennas, spaced 3.87λ or 1.95λ, fed 180° out of phase. Also see Kramar/Hahnemann's equivalent 1938 US patent 2241907, and Kramar's 1939 German 1-course expansion patent 2241915]
2212238 US 1938 Frederick A. Kolster Int'l Telephone Development Co. (part of Int'l Telephone & Telegraph Corp. (ITT), the parent company of C. Lorenz A.G. since 1930) --- "Ultra short wave course beacon" [100% copy of the Lorenz A/N with dipole & switched reflectors landing beam system, with operating frequency increased to higher VHF [30-150 MHz, vs. 30 MHz for standard Lorenz A/N system], so as to avoid night-effect / ionospheric distortions (but susceptible to reflections from terrain and man-made structures), with an added colocated beacon with figure-of-8 pattern for wide-angle approximate location by aircraft far from primary course lines]
2282030 US 1938 Henri Busignies Henri Busignies --- "System of Guiding Vehicles" [Ground-based D/F apparatus comprising 2 sets of 3 antennas (1x 3 orthogonal loops, 1x 3 orthogonal crossing dipoles), eliminating night effect and aircraft effect (transmitting with trailing antenna = horizontally polarized); 2 antennas of each set are connected via amplifiers to 2 pairs of oscilloscope deflection plates. The remaining antennas are alternately connected to a signal strength indicator via an amplifier.]
2290974 US 1938 Ernst Kramar C.Lorenz A.G. --- "Direction Finding System" [Method of indicating equisignal beam beacon (2 switched directional antennas or 1 omni antenna + 2 switched reflectors) course line deviation, by comparing amplitude of the 2 signals. Standard Visual Indicator (vibrating reeed) for use with non-keyed 2-tone equibeams does not provide acoustic deviation indication, but pilot requires both to be available simultaneously. Existing instruments for equisignal beam aural beacons are based on electrical pulses derived from the flanks of the received tone pulses (rectified tone-pulses ( = DC-pulses) are passed through a transformer ( = inductance), which creates a positive induction pulse for each rising flank of a DC pulse and a negative pulse for each falling flank, the pulse amplitude being proportional to the DC-pulse amplitude ( = relative tone strength). This only works with beam-keying with single elements per side (e.g., complementary E/T keying, with only dots on one side, only dashes on the other). However, with these, it is difficult to assess the course deviation by listening to the combined audio signals (except for very large course deviations, when only one sub-beam is received). Aural interpretation is better with complementary dots & dashes keying patterns where both characters have the same number of dots and the same number of dashes (A/N, D/U, etc.). However, these cannot be used with the existing "kicking meter" indicators. Patent fixes this limitation, by inserting a 2-tone filter + 2nd rectifier stage between the 1st rectifiers and the standard summing moving-coil meter. Filters tuned to the repetition rates of the positive (or negative) induction pulses (i.e., factor 2:1). Hence, meter decaying pulse reflections to one side for "A" and to the other side for "N". This is a co-patent / split-off of Kramar's 1939 US patent 2241915. Also see Kramar's 1931 US patent 1949256, and L.M.T. Co.'s 1937 French patent 816120, p. 99 in ref. 21B.]
2297228 US 1938 Ernst Kramar C.Lorenz A.G. --- "Glide Path Producing Means" [Equivalent to Kramar's 1937 German patent 720890]
2288196 US 1938 Ernst Kramar C.Lorenz A.G. --- "Radio Beacon System" [Equivalent to Kramar's 1938 German patent 731237, with some expansion.]
7105791 RP 1938 Ernst Kramar & Heinrich Nass C.Lorenz A.G. "Sendeanordnung zur Erzeugung von Leitlinien" "Arrangement for producing course guide-beams" [The standard "Lorenz Beam" equisignal beacon configuration ( = 1 vertical dipole + 2 reflectors, per Kramar/Lorenz 1932 German patent 577350) is based on complementary keying of the reflectors, and transmitting continuous single tone via the dipole. Equisignal "visual" beacons continuously transmit 2 overlapping sub-beams with different tones, which allows simpler indicator system. Patent modifies the "Lorenz beam" configuration, by not hard-keying the reflectors, but replacing their keying switches / relays with interruptors / variable capacitors / goniometers that are each driven by seperate motor; one motor with 90 rpm, the other with 150 rpm, resulting in 90 & 150 Hz modulation respectively ( = standard modulation tones of Visual Equisignal Beacons), and constant carrier transmitted via the dipole. However, without further measures, this this results in suppression of the equisignal course-lines! This is fixed by changing the reflector length and reflector-dipole spacing such that the deformed dipole patterns have less overlap. Same result if, instead of dipole & reflectors placed on a straight line, they are arranged as a triangle. Can be used with standard Visual Indicator (e.g., reeds). Also see Kramar/Nass's equivalent 1939 US patent 2238270]
2241907 US 1938 Ernst Kramar & Walter Max Hahnemann C.Lorenz A.G. --- "Landing Method and System for Aircraft" [Equivalent of Kramar's 1932 German patent 711673]
2238270 US 1939 Ernst Kramar & Heinrich Nass C.Lorenz A.G. --- "Radio Direction Finding System" [Equivalent of Kramar's 1938 German patent 710591]
2210664 US 1939 Ernst Kramar & Walter Max Hahnemann C.Lorenz A.G. --- "Radio Direction Finding System" [Equivalent to Hahnemann/Kramar's 1937 German patent 734130 (UHF beacon with horizontal diople just below ground level at the intended touch-down point (FD: i.e., per Diamond/Dunmore's 1933 US patent 2120241).]
525359 GB 1939 Frank Gregg Kear Frank Gregg Kear --- "Improvements in or relating to radio transmitting systems" [Equisignal beam beacon, with antenna configuration comprising 2 omni-directional antennas, spaced ½λ and alternately & complementary keyed in-phase and 180° out of phase, to create 2 overlapping cardioid patterns. Alternatively: 2 separately fed omni-antennas, physically spaced ¼λ, with bi-directional transformer-coupled ¼λ feedline between them (= 90° phase difference); can be generalized for X° physical spacing; antennas fed by transmitter(s) via transformers, either 2 tones (Visual Range) or complementary keyed Aural Range. With this arrangement and resulting sub-beam patterns, contrary to conventional 2-/4-course beacons, there is no need for TO/FROM switching on the indicator, as the same characteristic signal (keying pattern or tone) is always (i.e., for all 4 courses!) on the same side of the equisignal beams when flying FROM (or, conversely, TO) the beacon! Various transmitter / modulator-amplifier / transformer configurations.]
2255741 US 1939 Ernst Kramar C.Lorenz A.G. --- "System for determining navigatory direction" [Equivalent to Kramar's 1938 German patent 731237]
718022 RP 1939 Ernst Kramar C.Lorenz A.G. "Antennenanordnung zur Erzeugung einer Strahlung für die Durchführung von Flugzeugblinlandungen" "Antenna configuration for generating a beam for blind landing of airplanes" [Expansion of Kramar's 1938 German patent 711673]
2241915 US 1939 Ernst Kramar C.Lorenz A.G. --- "Direction-Finding System" [Expansion of Kramar's 1938 German patent 711673. Instead of a 2-course glide path beacon with 2 antennas spaced 3.87λ or 1.95λ and fed 180° out-of-phase, now a 1-course beacon based on same cardioid pattern concept, with 2 linear arrays with 3.87λ or 1.95λ spacing between array centers, each array comprising 4 antennas with ¼λ spacing, and the 2 arrays fed 180° out of phase.]
2272997 US 1939 Andrew Alford Int'l Telephone Development Co. (part of Int'l Telephone & Telegraph Corp. (ITT), the parent company of C. Lorenz A.G. since 1930) --- "Landing beacon system"  [2-transmitter beacon system, one producing landing beam with curved, constant field intensity approach path, the other (also) located on the approach course but displaced in the direction of the approach, its field combining with the first, so as to create a linear (straight) landing path.]
767254 RP 1939 Ernst Kramar C.Lorenz A.G. "Verfahren zur kontinuierlichen Ortsbestimmung eines Flugzeuges längs der Anflugstrecke zu einem Landeplatz" "Method for continuously determining position of an aircraft along a the approach path to an arfield"  [From marker beacon to touchdown, rotating wave interference pattern, one beam with phase modulation, one with unmodulated CW, wavelength at least approach path length, e.g., 900 m or 4 km, located at departure end of runway]
2294882 US 1940 Andrew Alford International Telephone & Radio Mfg. Corp. [subsidiary of ITT] --- "Aircraft Landing System" [methods & means for providing a glide path with antenna location remote from landing runway [FD: beside runway, abeam T/D point]; parabolic/curved GP too steep at higher alt, but correct shap at T/D point; straight GP at higher altitude but too sharp angle at T/D point; patent proposes hyperbolic GP shape that is substantially straight but curved at lower alt; antenna system has symmetrical pattern in opposite directions, i.e., 2 GP's in opposite directions (FD: undesirable, since only 1 can serve a correct T/D point!)
2404501 US 1940 Frank Gregg Kear Frank Gregg Kear --- "Radio beacon system" [VHF rotating-beam radio beacon with, e.g., 200-300 MHz carrier frequency; narrow beam rotates in azimuth at a constant rate (e.g., 12-30 rpm); the 360° azimuth is divided into a fixed number of consecutive arc-segments (e.g., 5° wide), starting with, e.g., north. The odd-numbered segments all have a different-but-fixed modulation tone. No transmission when beam sweeps through an even-numbered segment. E.g., with 5° wide arc-segments, 36 segments each with a distinct tone, interspersed with 36 no-tone segments. A receiver on an abritrary azimuth/course, will receive sequentially 3 tones: the strongest is the tone associated with the arc-segment in which that course lies; this is preceded by the (weaker) tone of the preceding arc-segment and followed by the (weaker) tone of the next arc-segment. Transmitter has tone-modulator with tone stepwise altered by same motor as rotating the directional antenna. Receiver has 3 audio filters with center frequency that is operator-selectable to the tone-combination of the desired & adjacent arc-segments. The tone of the center arc-segment directly drives a signal strength indicator. The other 2 tone filters are both followed by a slow-decay signal peak-capturing circuit, the outputs of which drive a zero-center meter, indicating relative strength (with sign) of the 2 adjacent arc-segment signals. Instrument provides continuous indication of deviation from any selectable course.]
2283677 US 1940 Armig G. Kandoian Int'l Telephone & Radio Mfg. Corp. --- "Localizer beacon" [ILS localizer system, 5 loop antennas, transmission line bridge, 2-tone continuous modulation]. Also see 1951 "Localizer antenna system" US patent 2682050 by A. Alford.
2288815 US 1940 David G.C. Luck Radio Corporation of America (RCA) --- "Omnidirectional radio range" [equivalent to the German UKW-Phasendrehfunkfeuer “Erich”; precursor to the post-WW2 VOR system]
581602 GB 1942 Robert James Dippy Robert James Dippy --- "Improvements in or relating to Wireles Signalling Systems" [invention of the Grid / GEE/ G hyperbolic system; covers GEE pulse-signals receiver & CRT display system design]
581603 GB 1942 Robert James Dippy Robert James Dippy --- "Improvements in or relating to Wireles Systems for navigation" [co-patent to Dippy's 1942 British patent 581602]
2436843 US 1943 Chester B. Watts & Leon Himmel Federal Telephone & Radio Corp. [subsidiary of ITT] --- "Radio Antenna" [UHF directional antenna system with 2 overlapping beams, radiating predominantly horizontally polarized waves, without rear lobes, suitable for operation with a mobile glide path transmitter, lower end of GP changes from straight GP angle to zero; finalization of US patent 2419552 (filed 1 month earlier) with same title, by Leon Himmel & Morton Fuchs]
862787 DP 1944 Joachim Goldmann C.Lorenz A.G. "Antennenanordnung zur Erzeugung von ebenen Strahlungsflächen der Strahlung Null" "Antenna configuration for generating narrow nulls in beam radiation pattern" [Invention of the "Elektra" multiple beam system]
148430 GB 1918 Hugo Lichte Hugo Lichte --- "Improvement in navigation by means of an alternating current cable located in the water" [inductive pilot-cable / leader-cable; also same-date French patent 524960]
163741 GB 1919 William Arthur Loth William Arthur Loth --- "Improvements in the system and apparatus for enabling a movable object to pursue an electrically staked out route in a more precise way than by means of visual points of reference" [inductive pilot-cable / leader-cable system for surface/submerged ships/boats, energized with electrical power with specific rhythms or frequencies.]
423014 DE 1919 William Arthur Loth William Arthur Loth "Empfangseinrichtung auf Fahrzeugen zur Navigation nach Führungskabeln" "Reception arrangement on vehicles for navigation by pilot-cables / leader-cables" [crossing loop antennas and "Telefunken Compass" switched dipoles in star-configuration]
410396 DE 1920 William Arthur Loth William Arthur Loth "Vorrichtung zur Navigierung von Fahrzeugenm insbesondere von Schiffen" "System for navigation of vehicles, in particular of ships" [crossed-loops receiver antenna for inductive pilot-cable / leader-cable system]
2224863 US 1938 Edward N. Dingley Edward N. Dingley --- "Blind landing equipment" [inductive pilot-cable / leader-cable system, cables in or on ground; with equi-signal; supplemented by 1938 US patent 2340282 and its equivalent 1938 GB patent 522345 ]
820319 GB 1950 Brian D.W. White National Research Development Corp. --- "Improvements in or relating to azimuth guidance systems" [aircraft azimuth guidance system; a wire supplied with AC power runs parallel with each side of the runway; the frequency of the supplies are either different or have the same carrier frequency with differing modulation frequencies and two equisignal fields exist along the runway center line; aircraft equipped with pick-up loop(s) to detect EM field and derive position relative to the wire(s) and runway center line.]

Table 3: Selected patents regarding radio direction finding, radio location, radio navigation through WW2


Note 1: due to copyright reasons, this file is in a password-protected directory. Contact me if you need access for research or personal study purposes.

red-blue line