Note - 1 June 2022: as announced since 2021, due to a large number of photos, diagrams, and other illustrations, the download size of this page had grown to about 40 MB! Depending on the user's internet access bandwidth, this page took "a while" to completely download. I have now split it into this main page and a dozen sub-pages.

• On this main page:
• [Introduction]
• [Radio direction-finding and radio-navigation terminology]
• [Radio direction-finding]
• [Transmitter technology]
• [Patents]
• [References]

• The Radio Navigation sub-pages:
• [German stepwise-rotating beam beacons: 1909-1918]
• [British constant-speed rotating beam beacons: 1916-1939]
• [The equi-signal beacon system of Otto Scheller: 1907 - today (incl. Radio Ranges & Instrument Landing System)]
• [Leader-cable course guidance systems]
• ["Blind" aerial bombing]
• ["Knickebein" - Luftwaffe rotable beam beacon for nav to bombing target]
• [ "X-system" and "Y-system" - Luftwaffe beam beacons for nav to bombing target]
• [Other Luftwaffe rotable/rotating beam beacon systems]
• [Hyperbolic radio navigation systems]
• [Radar systems for navigation: 1904 - 1945]
• [Transponder-based radio navigation systems]

• ["Bernhard/Bernhardine" Luftwaffe radio-navigation system]
• [FuG120 "Bernhardine" airborne Hellschreiber printer system]
• [FuSAn 724/725 "Bernhard" ground station]
• ["Bernhard" station locations]

©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: June 2022 (split into a dozen separate pages; added ref. 230R8, 245B-245D)

Previous updates: January 2022 (inserted section on bombing); December 2021 (added ref. 230Q5, 230Q6, 230R13); 28 May 2021 (note: now about 800 literature references provided on the WW2 Rad Nav pages, almost all downloadable!); April 2020 (started complete overhaul & expansion of this page).

INTRODUCTION

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:

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 (one-way, two-way):
• Ground-air (with air traffic control facilities)
• Air-air (with other aircraft)
• Navigation:
• Long-distance
• Short-distance
• 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.)
• Secondary aids (ground-operated or airborne radio Direction Finding systems, Distance Measuring Equipment)
• Collision avoidance:
• Hazardous weather phenomena (using 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 windshear detection systems also exist).
• Terrain (using 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 of "avoidance" 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 ,or other forms of "fake history". With few exceptions, history school books reflect the "winner's" point of view, and WW2 is no exception. 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..."

 

Fig. 2: The alternative to radio navigation....

(source: 1987, unknown)

TERMINOLOGY, CONCEPTS, PRIMARY PATENTS

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. 2: 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.

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)

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).

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:

Fig. 43A: Combining intersecting 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.

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:

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). Likewise, positioning based on WiFi networks (WPS), mobile/cellular telephone networks, etc. ahas added no new concepts! OK, passive radar is new.

TO BE ADDED: timeline diagram of technologies and specific systems discussed on the sub pages.

RADIO DIRECTION-FINDING

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.

Ref. 184A-184AA.

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.

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.

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".

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.

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 Marconi 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.

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.

TRANSMITTER TECHNOLOGY: 1865-1940

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.

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 radio communications took place in Germany 1909, when the Telefunken company installed a spark transmitter in a Parseval airship (ref. 186Y). In France and the USA, two-way wireless air-ground "Morse code" telegraphy (W/T) transmissions took place in the following year. 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 antennas, instruments and control panels, and sometimes a dedicated power supply (battery packs) or power 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 - quite 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 radio navigation. Finally, antennas typically protrude from the fuselage or wings. This causes drag - which reduces fuel range and maximum speed.

PATENTS

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.

REFERENCES

• Ref. 1: "Bernhard and Bernhardine", p. 24 in "Some historical and technical aspects of radio navigation, in Germany, over the period 1907 to 1945", Arthur O. Bauer, 28 pp. Source: www.cdvandt.org.
• Ref. 2: pages from the renowned books and other documents by Fritz Trenkle
• Ref. 2A: "Die deutschen Funkführungsverfahren bis 1945" ["The German radio guidance systems through 1945"], Fritz Trenkle, Dr. Alfred Hüthig Verlag, 1987, ISBN 3778516477, 236 pp.
• Ref. 2A1: p. 149 (X-Uhr / X-system clock).
• Ref. 2A2: pp. 76-110, 224.
• Ref. 2B: "Die deutschen Funk-Navigations- und Funk-Führungsverfahren bis 1945" ["The German radio navigation & guidance procedures through 1945"], Fritz Trenkle, Motorbuch Verlag, 1995, 208 pp., ISBN-10: 3879436150.
• pp. 62, 94-102.
• Ref. 2C: "Bordfunkgeräte - vom Funkensender zum Bordradar" ["On board radio equipment - from spark transmitter to radar"], Fritz Trenkle, Bernard und Graefe Verlag (publ.), 1986, 283 pp., ISBN 3-7637-5289-7. [table of contents]
• Ref. 2C1: p. 61-63 - "Kommandoübertragungszusätze" ["Command uplink accessories"].
• Ref. 2C2: p. 83-95 - "Eigenpeil- und Zielflug-Verfahren - LW-MW-Peil und Zielfluggeräte" ["RDF and reverse-RDF systems - LW/MW RDF & approach equipment"]
• Ref. 2C3: pp. 97-118 - "Leitstrahl-Verfahren" ["Guidance-beam systems"].
• Ref. 2C4: p. 108 - photo "Große Knickebein Anlage bei Kleve", ["Large Knickebein installation near Cleves"; note: incorrectly identified by Trenkle as station K4 at Kleve, instead of K2 at Bredstedt].
• Ref. 2C5: pp. 119-133 - "Drehfunkfeuer-Verfahren - LW, KW, UKW, DMW, bis 1945" ["Rotating-beam beacon systems, Longwave"].
• Ref. 2C6: pp. 134-140 - "Hyperbel-Navigations-Verfahren" ["Hyperbolic navigation systems"]
• Ref. 2C7: pp. 141-150 - "Entfernungsmeß-Verfahren" ["Distance measuring systems"]
• Ref. 2C8: pp. 198-200 - "Kenngeräte (Bord-Transponder)" [FuG 25 "Zwilling", FuG25a "Erstling"]
• Ref. 2D: "Versuch einer Zusammenstellung deutscher Funkgeräte 1939 ... 1945 LUFTWAFFE / HEER / MARINE (ca .1200 Geräte)" ["Attempt at a compilation of German radio equipment 1939 ... 1945 Air Force / Army / Navy (ca. 1200 equipment items)"], Wolfgang "Fritz" Trenkle, Issue VI.60 (1960), 100 pp. [file size: 38 MB]. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL 2-V/211, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016"
• Ref. 3: "Most probable position: A history of aerial navigation to 1941" [from hot air balloon to USA entry into WW2], Monte Duane Wright, University Press of Kansas (publ.), 1972, 280 pp.
• Book review by R.V. Jones, in "Journal of Navigation", Vol. 27, Iss. 4 , October 1974 , pp. 542-543. Source: en.booksc.org, accessed November 2021. [pdf]
• Book review by Gerald E. Wheeler, in "Military Affairs", Vol. 39, Nr. 1, February 1975, p. 43. Source: en.booksc.org, accessed November 2021. [pdf]
• Ref. 5: "Instruments of Darkness: The History of Electronic Warfare, 1939-1945", new ed., Alfred Price, Greenhill Books, 2005, 272 pp., ISBN-10: 1853676160; original edition: William Kimber and Co., Ltd, 1967. See note 1
• Ref. 5A: pp. 236-237; Same as pp. 274-275 in the excellent German translation: "Herrschaft über die Nacht: Spionen jagen Radar", Alfred Price, publ.: Bertelsmann Sachbuchverlag Reinhard Mohn, 1968, 304 pp., ASIN B0000BT35X.
• Ref. 5B: p. 82 - second of sixteen photo pages.
• Ref. 6: Transcribed reports from the British Air Ministry, Assistant Director of Intelligence (Prisoner Interrogation), A.D.I. (K) (a.k.a. "Felkin Reports", after their author). Source: The National Archives of the UK, ref. AIR40/2875 and 2876. Retrieved from www.cdvandt.org.
• Ref. 6A: §19-23 in "Some further notes on G.A.F. Pathfinder procedure" ["EGON" procedure, new EGON procedure, Berhardiner Gerät, Erika Gerät, Y-gerät, "X" Clock, Knickebein jamming],  S.D. Felkin, A.D.I.(K) Report No. 187/1944, 25 April 1944, 5 pp.
• Ref. 6B: §57-59 in "G.A.F. night fighters - R.A.F. Bomber Command countermeasures and their influence on German night fighter tactics" [transcript], S.D. Felkin, A.D.I.(K) Report No. 599/1944, 2 November 1944, 16 pp.
• Ref. 6C: "G.A.F. Night Fighters - Recent Developments in German Night Fighting",  S.D. Felkin, A.D.I. (K) Report No. 125/1945, January 1945, 18 pp.
• Ref. 6D: "The GAF (German Air Force) Signals Organisation in the War" [incl. X-System, X-beam, Knickebein, Y-System (Benito), Zyklop/Cyclop, Erika, Sonne beacons in Spain, radar, FuG25/25A, IFF, Panorama, Centimetre Wave R&D, Egon, Gee, H2S, Berlin-Gerät, Kammhuber night fighting, Window, Wilde Sau, HS293], Samuel Denys Felkin, A.D.I.(K) Report No. 334/1945, 1 July 1945, 27 pp.
• Ref. 6E: "Equipment of a Y-Site" [Berta I, Berta II, S16B, Sadir 80/100, Heinrich I (Peiler, D/F), Heinrich III, FuG 16ZE, FuG16ZY], S.D. Felkin, A.D.I.(K) Report No. 527B/1944, 25 Sept 1944, 13 pp.
• Ref. 6F: "Radio and Radar Equipment in the Luftwaffe- I. Blind Landing and Airborne Communications Equipment" [report of interrogations of General Martini and other PoW's; topics: LFF, JLFF, Fu Bl 2, AWG 1, FuG 10 P, FuGe 16, FuGe 17, FuGe 18, FuGe 15, FuGe 24, FuGe 29], S.D. Felkin, A.D.I.(K) Report No. 343/1945, 1 July 1945, 6 pp.
• Ref. 6G: "Radio and radar equipment in the Luftwaffe - II: Navigational aids" [D/F loop equipment, PeGe 6, FuG 141, FuG 142, FuG145; homing beacons: Schwanboje, Biene; beam systems: Zyklop, Sonne, Mond, Stern, Dora, Komet, Erika, Bernhardine, Hermes/Hermine; Pulse systems: Ingolstadt, Truhe, Baldur, Baldur-Truhe, Baldur-Bernhardine; Ground control systems: Benito = "Y", Egon, Nachtlicht, Nachtfee, Barbara, Barbarossa, Rübezahl], S.D. Felkin, A.D.I. (K) Report No. 357/1945, 25 April 1944, 18 pp.
• Ref. 6H: "Radio and radar equipment in the Luftwaffe - III: Electric altimeters" [FuG 101A, FuG 102, FuG 103, FuG 104], S.D. Felkin, A.D.I. (K) Report No. 362/1945, 27 July 1945, 3 pp.
• Ref. 6J: "Fighter defence of Germany - Control of fighters by the "Y" Procedure", Samuel Denys Felkin, A.D.I.(K) Report No. 525/1944.
• Ref. 6K: "German knowledge of 'OBOE'", [transcript], S.D. Felkin, A.D.I. (K) Report No. 318/1944, 29 Juni 1944, 11 pp.
• Ref. 6L: "Further Report on the Crew of the Ju.88 8-3 Z6 + FH of 1/K.G.66) shot down by A.A. 5 miles N.W. of Alost, on 23rd January 1945.(Previous A.D.I.(K) Report No.142/1945)" [incl. special navigation aids: EGON, "Y" procedure, "Y" clock, new "X" procedure = "Y" + EGON, FuG 28, Y-Clock (CRT), FuG 17, FuG 25A, FuG 217, Ju-88], S.D. Felkin, A.D.I. (K) Report No. 175/1945, 19 February 1945.
• Ref. 6M: "A G.A.F. Pathfinder Unit - Further report on Ju.88 S-1, Z6+IN, of 5/K.G.66, brought down in the sea off Brighton on 25th March 1944", Samuel Denys Felkin, A.D.I.(K) Report No. 160/1944 (prev. No. 141/1944).
• Ref. 7: "Beiträge der Firma Siemens zur Flugsicherungstechnik und Luftfahrt-Elektronik in den Jahren 1930 bis 1945 (Teil 1 & 2)", H.J. Zetzmann, in "Frequenz - Zeitschrift für Schwingungs- und Schwachstromtechnik"
• Ref. 7A: Part 1: Vol. 9, Nr. 10, October 1955, pp. 351-360. [Wassermann radar FuMG 402, Wellenschieber, Jagdschloß / FuMH 404, PPI, Freya FuMG 41, Würzburg Riese]
• Ref. 7B: Part 2 (pp. 387, 388, 392): Vol. 9, Nr. 11, November 1955, pp. 386-395. [RDF antennas for aircraft, Bernhard/Berhardine, transponder DME, D 2002, Kurskoppler, autopilot, FuG 135 Boden-Bord Kommando-Übertragungsgerät]
• Ref. 8: "General Electric funds Hitler", Chapter 3 in "Wall Street and the Rise of Hitler", Antony C. Hutton, G S G & Associates Publ., June 1976 (reprint), 162 pp., ISBN 0945001533.
• Ref. 13: p. 405 and 4.09 in "Japanese Electronics", OPNAV-16-VP101, Photographic Intelligence - Report 1, U.S. Navy Dept., Office of the Chief of Naval Ops., Air Intelligence Group, Div. of Naval Intelligence, Naval Photographic Intelligence Center, January 1945, 166 pp. [file size: 33 MB]
• Ref. 14: summary item 27 in "The German Wartime Electricity Supply - Conditions, Developments, Trends", British Intelligence Objectives Sub-comittee (BIOS), Final Report 342, Item No. 33, 28 selected pages. Source: www.cdvandt.org.
• Ref. 15: "Beschreibung und Betriebsvorschrift für Funk-Navigationsanlage FuG 120" [Description and Operating Manual for Radio-Navigation System FuG 120 "Bernhardine", with 2-channel Hellschreiber radio-navigation printer], Telefunken G.m.b.H., document FN-T-GB Nr. 1932, December 1944, 43 pp. [File size: 66 MB; a good-but-lower resolution file is here 26 MB]
• Ref. 19: p. 122 in "Die Erprobungstelle Rechlin", Christoph Regel, pp. 60-149 in "Flugerprobungsstellen bis 1945: Johannisthal, Lipezk, Rechlin, Travemünde, Tarnewitz, Peenemünde–West", Heinrich Beauvais, Max Mayer, Bernard & Graefe Verl., 1998, 364 pp., ISBN: 3763761179; Vol. 27 of "Die deutsche Luftfahrt : Buchreihe über die Entwicklungsgeschichte der deutschen Luftfahrttechnik", Theodor Benecke, Deutsches Museum
• Ref. 20: pp. 59-63 of "Richt- und Drehfunkfeuer" ["Directional and rotating radio beacons"; 4-Course, Telefunken Compass, Bernhard, Erika, Komet, ILS/LOC/GS], Chapter 3 of “Leitfaden der Funkortung: Eine systematische Zusammenstellung der Verfahren und Anlagen der Funkortung“ [Guide to radio location: a systematic survey of radio location methods and installations], Vol. 1 of "Lehrbücherei der Funkortung", Walter Stanner, 4^th ed., Deutsche RADAR-Verlagsgesellschaft m.b.H., 1957, 160 pp.
• Ref. 28: "Ernst L. Kramar Pioneer Award 1964", in "IEEE Trans. on Aerospace and Electronic Systems", Vol. 11, Issue 2, AES-2, No. 4, June 1964, pp. 81-85 [pdf]
• Ref. 31: "Das Funk-Blindlandegerät" [Fu Bl I, EBl 1, EBl 2, Fu Bl 2], Werner Thote, in "Radiobote", Vol. 2, Nr. 9, May-June 2007, pp. 20-25. Source: radiobote.at. [pdf]
• Ref. 32: "Beschreibung und Betriebsvorschrift für Funklande-Empfangsanlage Fu Bl 1 Ex" [Description and operating instructions for landing receiver system Fu Bl 1 Ex"], DTA 140, C. Lorenz AG, 1940, 59 pp. Source: www.cockpitinstrumente.de
• Ref. 33: pp. xxxxx in "Confound and Destroy: 100 Group and the bomber support campaign", Martin Streetly, Jane's Publishing, Inc. (publ.), 1978, 379 pp. [pdf, file size 35 MB]. See note 1
• Ref. 35: pp. 8-11, 33 in "The Hut Six Story - Breaking the Enigma Codes", Gordon Welchman, M & M Baldwin Publ., 6^th ed., 2011, 263 pp.
• Ref. 38: documents of the Sub-Committee for the Investigation of German Electronic and Scientific Organisation (SIGESO). Source: www.cdvandt.org.
• Ref. 38A: "Navigational Aids for Bombers" [Knickebein, X, Y, Benito, Erika, Sonne, Zyklop], sheet 3-6 in Section 0.1 of A.L. No. 46 of SIGESO, 12/12/1945, Report Vol. 1, Part 2. 
• Ref. 38B: "The Goldwever System of Navigational Aid for U-Boats", sheet 30 in Section 2.2, A.L. No. 61 of SIGESO,12/2/46.
• Ref. 39: Luftwaffe manuals for ground and on-board landing beam systems element. Source: www.cdvandt.org. Retrieved: January 2018, September 2020.
• Ref. 39A: "Funk-Landegerät Fu Bl I - Geräte-Handbuch, Beschreibung und Betriebsvorschrift", Luftwaffe Druckschrift D. (Luft) T.4065, April 1942, 50 pp.
• Ref. 39B: "UKW-Landefunkfeuer 120 Watt und 500 Watt, Aufbau-Anweisung", Luftwaffe Druckschrift D. (Luft) T.4458, June 1943, 8 pp.
• Ref. 39C: "AS 4 Anflugführungssender 4 - Geräte-Handbuch", Luftwaffe Druckschrift D. (Luft) T.4456, June 1943, 36 pp.
• Ref. 39D: "Ansteuerungs-Sender AS 2 - Geräte-Handbuch, Beschreibung und Wirkungsweise sowie Bedienung und Wartung", Luftwaffe Druckschrift D. (Luft) T.4452, May 1941, 38 pp.
• Ref. 39E: "Antenne AFFA 2- Geräte-Handbuch, Beschreibung und Wirkungsweise sowie Bedienung", Luftwaffe Druckschrift D. (Luft) T.4454, September 1941, 17 pp.
• Ref. 39F: "Beschreibung und Betriebsvorschrift für 5 Watt-Ultrakurzwellen-Einflugzeichensender EZS 2", Luftwaffe Druckschrift D. (Luft) T.4451, February 1941, 30 pp.
• Ref. 39G: "Beschreibung und Betriebsvorschrift für Funkfeuer-Kontrolempfänger EBKS", Luftwaffe Druckschrift D. (Luft) T.4450, February 1941, 17 pp.
• Ref. 39H: "120 Watt UKW Leitstrahlsender AS 3" ["UKW Landefunkfeuer, ortsfest"; non-mobile VHF landing beam beacon], Beschreibung Nr. 75/710, C. Lorenz AG, Berlin-Tempelhof, November 1942.
• Ref. 40: documents about FuG 16 and FuG17
• Ref. 40A: "Die Bordfunkgeräte FuG 16 und FuG 17", pp. 28-49 in "Berühmte Bordfunkgeräte - ein Beitrag zur Geschichte der Elektrotechnik" [FuG10, FuG16, FuG17, FuG25a, FuG101a, ...], H. Sarkowski, Expert Verlag, 1983, 80 pp.
• Ref. 40B: "Bordfunkgerät FuG 16 ZY mit Aufbauvorschrift für Antenne des Zielflug-Senders", Luftwaffe Druckschrift D.(Luft)T.4069, 5 August 1944, 114 pp. Source: cdvandt.org.
• Ref. 40C: "Das Bordfunkgerät FuG17", Heft 205 of "Teil 1 - Gerätebeschreibungen" of Luftwaffe Druckvorschrift L.Dv.702/1, April 1941, 28 pp. Source: cdvandt.org, accessed 23 September 2020.
• Ref. 41: documents about airships (Zeppelins, dirigibles, ...)
• Ref. 41A: "Zeppelins over England", Kenneth Poolman, White Lion Publishers (publ.), 1975, 224 pp. Originally published in 1960 by Evans Brothers Ltd. Source: worldhistory.biz, accessed 27 May 2021. [pdf].
• Ref. 41B: "Funkeinrichtung des Zeppelin-Luftschiffes LZ 129" ["Radio equipment of the Zeppelin airship LZ 129 "Hindenburg"], in "Radio-Amateur", Vol. 13, May 1936, 3 pp. Source: dokufunk.org, retrieved 10 June 2021.
• Ref. 41C: "Die Funkeinrichtung des Zeppelin-Luftschiffes LZ 129" ["Radio equipment of the Zeppelin airship LZ 129 "Hindenburg"], T. Pd., in "Zeitschrift:Pionier : Zeitschrift für die Übermittlungstruppen", Vol. 9, Nr. 5, May 1936, pp. 89-93. Source: e-periodica.ch, retrieved 11 June 2021 -- same as ref. 41B, better legible, but without images.
• Ref. 41D: "Die großen Zeppeline - Die Geschichte des Luftschiffbaus" ["The large Zeppelins - The history of airship construction"; German, British, US American], Peter Kleinheins, Wolfgang Meighörner (ed.), 3^rd ed., Springer (publ.), 2004, 273 pp.  [pdf, file size: 58 MB; lower-res version is here, 10 MB] See note 1
• Ref. 41E: pp. 82-83 in "Funkeinrichtung", chapter 9 in "LZ 129 "Hindenburg" - Das Luftschiff des deutschen Volkes", Werner von Langsdorff, H. Bechhold Verlagsbuchhandlung (publ.), 1936, 96 pp.
• Ref. 77: "History of the German night fighter force, 1917-1945", Gebhard Aders, Jane's Publishing Company, 1^st ed., 1979, 284 pp. [file size 62 MB].  See note 1
• This is the translated and edited version (by A. Vanags-Baginskis and B. Gallagher) of the original German version "Geschichte der deutschen Nachtjagd: 1917-1945", Gebhard Aders, Motorbuch Verlag (publ.), 1977, 391 pp.
• Ref. 77A: pp. 96, 182.
• Ref. 77B: pp. 194, 195.
• Ref. 77C: pp. 246, 237.
• Ref. 90:
• Ref. 90A: private message to me in March of 2015 in the Axis History Forum.
• Ref. 90B: pp. 21, 57, 58 in "Stations radar et radio-navigation sur le Mur de l'Atlantique - Spécial Normandie d'Antifer à Granville", Alain Chazette, Bernard Paich, Alain Destouches, Jacques Tomine, Jörg Poweleit, Michaël Svejgaard, Histoire & Fortifications (publ.), 2015, 96 pp
• supplement: "Stations radar et de radio-navigation sur le Mur de l'Atlantique (complement photos)", 32 pp.
• Ref. 90C: p. 161 in "Stations radar et radio-navigation sur le Mur de l'Atlantique - Volume 2 -Spécial Belgique - Nord - Pas-de-Calais - Picardie - Haute-Normandie", Alain Chazette, Bernard Paich, Pierre Nowak, Alain Destouches, Jacques Tomine, Ingrid Paindavoine, Histoire & Fortifications, 2016, 160 pp.
• Ref. 90D: "Drawing of a Funk Sende Anlage Bernard 724/725 bunker", 14-March-2015 thread in Axis History Forum; used with permission
• Ref. 90E: "German Military Symbols", U.S. War Dept., General Staff, Military Intelligence Service, January 1943, 152 pp. (public domain, no ©)
• Ref. 93: pp. 115-117 in "The High-Frequency War - A Survey of German Electronic Development", E.S. Henning, HQ Air Materiel Command (AFMC), Wright Field, Dayton/OH, Summary report No. F-SU-1109-ND, 4 June 1946 (US Gov't, hence no copyright).  [file size: 225 MB; a lower-resolution version is here, 56 MB]
• Ref. 110: articles from "IEE Proceedings Part A "Physical Science, Measurement and Instrumentation, Management and Education Reviews", The Institution of Electrical Engineers (publ.), Vol. 132, Issue 6, October 1985. Source: en.booksc.org, accessed 4 November 2021.
• Ref. 110A: "Editorial - historical radar", E.H. Putley, pp. 325-326, [pdf], See note 1.
• Ref. 110B: "Memories of radar research", J.D. Cockcroft, pp. 327-339, [pdf], See note 1.
• Ref. 110C: "The work of TRE in the invasion of Europe", J.W.S. Pringle, pp. 340-358, [pdf], See note 1.
• Ref. 110D: "ASV: the detection of surface vessels by airborne radar",  R.A. Smith, R. Hanbury-Brown, A.J. Mould, A.G. Ward, B.A. Walker, pp. 359-384, [pdf], See note 1.
• Ref. 110E: "The development of centimetre AI", W.E. Burcham, pp. 385-393, [pdf], See note 1.
• Ref. 110F: "Oboe: history and development", A.H. Reeves, A.H., J.E.N. Hooper, pp. 394-398, [pdf], See note 1.
• Ref. 110G: "H2S and the navigator", E.L. Killip, pp. 399-400, [pdf], See note 1.
• Ref. 110H: "Historical note on H2S", A.C.B. Lovell, pp. 401-403, [pdf], See note 1.
• Ref. 110J: "The new H2Ss", J.B. Smith, pp. 404-410, [pdf], See note 1.
• Ref. 110K: "History of fighter direction", N. Orgel, pp. 411-422, [pdf], See note 1.
• Ref. 110L: "The radio war" [TRE, 80 Signals Wing, 100 Group, Knickebein, X-System, Y-System/Wotan/Benito, Jostle, Ground Grocer, Mandrel, Moonshine, Würzburg], Robert Cockburn, pp. 423-434, [pdf], See note 1.
• Ref. 110M: "The story of IFF (Identification Friend or Foe)", Lord Bowden of Chesterfield, pp. 435-437, [pdf], See note 1.
• Ref. 110N: "Development of radar for the Royal Navy 1935-44", J.D.S. Rawlinson, pp. 441-444, [pdf], See note 1.
• Ref. 119: "1939, Husum wieder Soldatenstadt", Jürgen Dietrich, 8 pp. in "300 Jahre Garnisonsstadt Husum - 50 Jahre Bundeswehrstandort", H. Hünken, H. Sehnert (eds.), 2006, 73 pp.  [pdf]
• Ref. 120: personal correspondence with R. Grzywatz, February 2014
• Ref. 132: Location of airfields used by German, US, and GB air forces during WW2 and German defence lines
• Ref. 132A: "Luftverteidigungszone West" page of Forschungsgruppe Untertage e.V.  [pdf]
• Ref. 132B: "Fliegerhorste - und Einsatzhäfen der Luftwaffe"
• Ref. 132C: "Luftwaffe Airfields 1935-1945", Henry L. deZeng   [pdf]
• Ref. 132D: Brief biography of Lieutenant General Karl Kitzinger, Landeskunde entdecken online Baden-Württemberg (LEO-BW), Landesarchiv Baden-Württemberg  [pdf]
• Ref. 132E: "UK airfield listing" (RAF and USAF)
• Ref. 132F: "Flugplätze der Luftwaffe 1934 - 1945 und was davon übrig blieb - Gesamtverzeichnis", Jürgen Zapf, 2010, 568 pp.
• Ref. 132G: "Luftwaffe night fighter control methods", Michaël Svejgaard, accessed 1 June 2020.  [pdf of web page snapshot;  actual web page is subject to change]
• Ref. 132H: Airfields of Britain Conservation Trust
• Ref. 137: "Ausstrahlung, Ausbreitung und Aufnahme Elektromagnetischer Wellen" ["Radiation, propagation, and absorption of radio waves"], Ludwig Bergmann, Hans Lassen, Vol. 2 of "Lehrbuch der drahtlosen Nachrichtentechnik" ["Textbook of wireless communication"], Nicolai von Korshenewsky (ed.), Wilhelm T. Runge (ed.), Springer -Verlag (publ.), 1940, 286 pp. Source: libarch.nmu.org, retrieved 18 May 2020. [file size: 22 MB]
• Ref. 137A: "Die Dipolreihe, Dipolgruppe, und Dipolebene" ["The dipole row, dipole array, dipole plane"], pp. 62-73.
• Ref. 137B: "Richtantennen für Leitstrahlanordungen (Funkbaken)" ["Directional antennas for guide-beams (radio beacons)"], p. 97-98 in Chapter II.
• Ref. 140: "Zum 75 jährigen Bestehen der Firma Hein, Lehmann & Co., A.-G., Düsseldorf. 1888 - 1963", Hein, Lehmann & Co., 1963, 123 pp.
• Ref. 151: p. 16, 17, 22 in "Jagdschloß A (Lehrunterlagen) Teil I", 2^nd ed., Lehrschule für Fernmeldetechnik, Detmold, November 1944, 115 pp. Source: www.cdvandt.org
• Ref. 164: documents of the Combined Intelligence Objectives Sub-Committee (CIOS). Source: cdvandt.org.
• Ref. 164A: "Institutes of the Bevollmaechtigter fuer Hochfrequenz-Forschung", CIOS, Item No. 1 & 7, File No. XXXI-37, May 1945, 215 pp.; source: cdvandt.org.
• Ref. 164B: "The I.T.T., Siemens and Robert Bosch Organizations" [incl. Lorenz: Elektra, Sonne, Mond, Knickebein, Erika, Goldwever, Hermes/Hermine, 6-mast Lorenz Adcock D/F based on British patent, Lorenz Blind Approach/Landing, IFF, radar], CIOS, Item No. 1, 7 & 9 (Radar, Signal Communications, Physical & Optial Instruments and Devices), File No. XXXI-38. Source: cdvandt.org. Retrieved 22 September 2019.
• Ref. 164C: "Report on C. Lorenz A.G." [history, factories, relationship with Philips & Telefunken, Stuttgart UHF radio link (FuG0s, FuG03a), Feuerzauber & Feuermolch Oboe-jammer, FuG200, FuG226/Neuling], CIOS, Item No. 1, File No. XXV-12, 13 pp. Source: cdvandt.org. Retrieved 7-Feb-2020.
• Ref. 164D: "Beacon Transmitters", in "Inspection of Philips Works at Eindhoven", Robert Watson Watt, CIOS Target Number 1/42, CIOS file No. III-1, 23-26 September 1944, 56 pp. Source: cdvandt.org. Retrieved 27 March 2022.
• Ref. 172: copy of item in file AIR 29/284 "Central Interpretation Unit (CIU) Medmenham; Interpretation reports and aerial photos (1943)". Item is in the collection of The National Archives; material with UK Crown Copyright, used in accordance with the Open Government License [pdf].
• Summary of the contents of ref. 172A.
• Ref. 172A: "German “Windjammer” R.D.F. Stations", part of "Monthly interpretation review for July 1943", 7 pp.
• Ref. 173: copy of items in file AIR 14/3577 "Signals investigation on 27 to 35 Mc/s "Windjammer" (1943/1944)". Items are in the collection of The National Archives; material with UK Crown Copyright, used in accordance with the Open Government License [pdf].
• Summary of the contents of ref. 173A-173E.
• Ref. 173A: "Windjammer" observation", by R.A. Fareday (Noise Investigation Bureau [Electronic Intelligence], N.I.B., London), dated 20^th June 1944, 1 page.
• Ref. 173B: "Possible "Windjammer" transmissions", report by Flight Lieutenant Douglas of 192 Sq., dated 16^th December 1943, 1 page.
• Ref. 173C: "192 Squadron Flight report No. 215/43" by F/Lt Robinson to Squadron Leader Burtler, dated 15^th November 1943 (actual report by P/O G.F. Evans of 13^th November 1943), 6 pages.
• Ref. 173D: "Windjammer – Arcachon", letter from Air Ministry A.I.4. [intelligence branch section supervising RAF Y Service] to Commanding Officer of 192 Squadron, dated 16^th July 1943, 1 page + 1 aerial photo.
• Ref. 173E: "The Windjammer and Dreh-Elektra", by 192 Squadron Leader J. Whitehead, dated 18^th June 1943, 1 page.
• Ref. 174: copy of items in file AIR 14/3594 "Windjammer" [ = "Bernhard"] station: photographs and interpretation reports. Includes vertical and low oblique aerial photographs of "Windjammer radar" sites in Germany and France (1943/1944)". Items are in the collection of The National Archives; material with UK Crown Copyright, used in accordance with the Open Government License [pdf].
• Summary of the contents of ref. 174A-174J.
• Ref. 174A: Letter entitled "W/T Bergen/Belvedere" by Squadron Leader C.W. Swanell on behalf of the Group Captain commanding R.A.F. Station Medmenham to R.V. Jones (A.D.I. Science), dated 9^th April 1943, 1 page + 1 photo
• Ref. 174B: Aerial photo of station "Bergen/Belvedere" [The Netherlands], photo No. 3022, taken 22^rd March 1943 by 541 Squadron
• Ref. 174C: Letter entitled "W/T – Bergen/Belvedere" by Group Captain commanding R.A.F. Station Medmenham to R.V. Jones (A.D.I. Science), dated 9^th April 1943, 1 page. (note: photos referenced in letter not on file)
• Ref. 174D: Letter entitled "W/T Desvres/Le Bois Julien" on behalf of Group Captain commanding R.A.F. Station Medmenham to R.V. Jones (A.D.I. Science), dated 15^th November 1942, 1 page + 2 photos.
• Ref. 174E: Letter entitled "W/T: Desvres/Le Bois Julien" on behalf of Group Captain commanding R.A.F. Station Medmenham to R.V. Jones (A.D.I. Science), dated 29^th March 1943, 1 page + 1 photo.
• Ref. 174F: "Interpretation Report No. G. 308" dated 28^th June 1942, of aerial photos taken over Desvres/Le-Bois-Julien at altitude of 20k ft during Sortie A/945 on 20^th June 1942, 1 page + 1 photo.
• Ref. 174G: "Interpretation report No. G.590" dated 6^th October 1942, of aerial photo taken over locality Morlaix, W/T station Mt. St. Michel, at altitude of 12k ft during Sortie Q/21 on 24^th September 1942, 2 pages + 1 photo.
• Ref. 174H: Letter entitled "W/T: Pouzauges/St.Michel-Mont-Mercure" on behalf of Group Captain commanding R.A.F. Station Medmenham to Squadron Leader Whitehead (A.I.4), dated 29^th March 1943, 1 page + 3 photos.
• Ref. 174J: Photos No. 4065 and 4066 of station at St. Vaast / La Pernelle, taken 31^st March 1943 from off shore. [station is fully, though vaguely, visible on horizon]
• Ref. 177: post-war letters [in German] from the company "Hein, Lehmann & Co. Eisenkonstruktionen, Brücken- und Signalbau K.-G." in Berlin-Tempelhof to Telefunken in Berlin, with claims ("Altforderungen") regarding delivery and installation of various types of antenna systems (arrays, tube & lattice masts, wooden masts, metal-clad wooden huts, verticals, dishes, turntables, for "Bernhard", "Marius", "Marius II", "Uran II", "Forsthaus-KF", etc.), installations in Germany, Hungary, Monte Carlo, Croatia, etc., during the period of July 1942 through the end of the war (8 May 1945); source: corporate archives of DTM Berlin, I.2.060C-00541:
• Ref. 177A: Letter from Hein, Lehmann & Co. to Telefunken with payment status of 17 Telefunken purchase orders and the resulting outstanding significant claim; dated 19 June 1949, 2 pp.
• Ref. 177B: Letter from Hein, Lehmann & Co. to Telefunken with adjusted claims, based on assessment of Telefunken counter-claims; dated 19 June 1950, 8 pp.
• Ref. 177C: Letter from Hein, Lehmann & Co. to Telefunken, with further justification for claims regarding delivery & installation of 12 "Bernhard" antenna systems (against purchase order of July 1941) for Be-2 - Be-8 and Be-12, of 6 associated "Dioden-Masten" antenna masts (based on price quote of September 1941), and delivery (without installation) of the antenna systems of Be-1 and Be-9 - Be-11; dated 5 February 1951, 3 pp.
• Ref. 178: Reichsmark vs. US Dollar and Euro exchange and equivalency data:
• Ref. 178A: "Deutsche Bundesbank - Average Currency Exchange Rates 1908-1951 Mark / Reichsmark / Deutsche Mark (M/RM/DM) vs. France FRF / Austria K, S / USA $ / UK £ / Netherlands HFL", Vs 801, 12 pp. Retrieved 2017 [pdf]
• Ref. 178B: source of US dollar inflation (CPI, buying power) calculator: www.usinflationcalculator.com.
• Ref. 178C: Tabulated exchange rate of Reichsmark to US$, with conversion to 2016 US$ and Euro, Frank Dörenberg, 21 May 2017; based on ref. 178A/B.
• Ref. 181: "Drehfunkfeuer System Telefunken - Teil 1: Verfahrensbeschreibung EC1-4262" [Telefunken rotating radio beacon, part 1: description of the method], Adalbert Lohmann, Berlin, October 1942, 129 pp., copy nr. 29, personal copy of Albrecht Leyn [note: this document was never printed, other than a very limited number of personal copies, individually approved by Dept. LC-4 (Technisches Amt) of the RLM; ref. 183]; source: corporate archives of DTM Berlin, part of file nr. I.2.060C-06172  [file size: 62 MB; a lower-resolution version is here, 28 MB]
• Ref. 183: "Das Drehfunkfeuer-Verfahren Bernhard und Bernhardine, System Telefunken" ["Verfahrensbeschreibung Bernhard, Bernhardine", description of the Bernhard-Bernhardine method], Adalbert Lohmann, Telefunken Gesellschaft für drahtlose Telegraphie m.b.H., Berlin-Zehlendorf, Telefunken document EC 1 4310, July 1943, 28 pp., copy nr. 11; source: corporate archives of DTM Berlin, file nr. I.2.060C-04403.
• Ref. 184: radio direction finding
• Ref. 184A: articles on Watson-Watt direction finding method
• Ref. 184A1: "Basics of the Watson-Watt Radio Direction Finding Technique", RDF Products Web Note WN-002, December 1998, 12 pp. Source: www.rdfproducts.com, accessed 3 March 2020. [pdf]
• Ref. 184A2: "Busting Watson Watt DF ambiguity - maths edition", David A Moschella, cyntony.com blog post, 13 July 2017. Accessed 16 March 2020. [pdf]
• Ref. 184A3: "Adcock/Watson-Watt Radio Direction Finding", Ismael Pellejero Ibáñez (EA4FSI) Technical Articles, 15 August 2012. Accessed 3 March 2020. [pdf]
• Ref. 184A4: "Über den Rahmeneffekt eines aus vertikalen Linearantennen bestehenden Adcock-Peilers: Der Zusammenbruch eines Dogmas" ["Loop effect of an Adcock D/F - the collapse of a dogma"; Adcock Watson-Watt configuration does not always eliminate horizontally polarized signals], Gottfried Eckart, pp. 151-178 in "Sitzungsberichte", Verlag der Bayerischen Akademie der Wissenschaften (publ.), 1 January 1972, 28 pp.  [pdf]
• Ref. 184B: "Het radio-peilen" ["Radio D/F"; in Dutch language; DF, multi-path, Telefunken Compass toroidal coil coupling, radio goniometer, rotating loop, fixed-course crossing loop pair, night effect, shoreline effect], Anthonet Hugo de Voogt, pp. 74-94 in "Tijdschrift van het Nederlandsch Radiogenootschap", 23 April 1921. Source: kivi.nl (Deel 01), accessed 18 March 2020.
• Ref. 184C: "Antennas for radio direction finding (RDF)", Chapter 23 (pp. 439-456) in "Practical Antenna handbook", 4^th ed., Joseph J. Carr, McGraw-Hill, 2001, 625 pp.
• Ref. 184D: "Summary Technical Report", E.C. Jordan et al, Technical Report No. 4, The Radio Direction Finding Research Laboratory, Dept. of Electrical Engineering, University of Illinois, Urbana/IL/USA, 15 April 1948, 70 pp. Source: Defense Technical Information Center (DTIC). Accessed 12 March 2020. [pdf] [Summary]
• Ref. 184E: "1957 Pioneer Awards in Aeronautical and Navigational Electronics: Alessandro Artom" [invention of the radio goniometer by Alessandro Artom, i.e., before Bellini & Tosi], Robert I. Colin, pp. 44-47 in "IRE Trans. on Aeronautical and Navigational Electronics", Vol. ANE-4, Issue 2, June 1957 [pdf]
• Ref. 184F: "Sammlung der Vorträge anlässlich der Arbeitstagung "Navigation", Arbeitskreis "Navigation", Bevollmächtigte der Hochfrequenzforschung ["Collection of presentations made at the workshop of the "Navigation" working group of the Commissioner for RF Research"], held at the Ferdinand Braun Institute, Landsberg am Lech, Germany, 23/24 March 1944. Source: cdvandt.org. Accessed 14 March 2020.
• Ref. 184F1: "Über grundsätzliche Fragen der Richtungs- und Entfernungsmessung" ["About fundamental questions regarding radio direction and distance measurement"], Paul von Handel, pp. 9-26. [pdf]
• Ref. 184F2: "Funknavigation mittels Laufzeitverfahren auf Kurzwelle" ["Short-wave radio navigation by means of time-of-flight method"], W. Dieminger, pp. 54-67. [pdf]
• Ref. 184F3: "Empfangs- und Peilanlagen mit gebündelter Charakteristik (Sektorpeilanlagen)" ["Directional reception and DF installations (sector-DF)"; RDF "Guben", "Wullenwever, "Brommy"], Hermann Janssen, pp. 98-120.  [pdf]
• Ref. 184F4: "Möglichkeiten und Grenzen der Richtungsmessung mit Raumwellen" ["Possibilities and limitations of direction measurement with skywaves"], Wilhelm Crone, 28 pp. [pdf]
• Ref. 184F5: "Registrierverfahren für Ionospärenmessungen" ["Printer for ionospheric measurements"], John Petersen, 5 pp.  [pdf]
• Ref. 184G: "Reduction of Night Error in Radio Direction-Finding Equipment for Aerodromes", H. Busignies, in "Electrical Communication - A Journal of Progress in the Telephone, Telegraph and Radio Art", Int'l Standard Electric Corp., Vol. 16, No. 3, January 1938, pp. 213-232. Source: www.worldradiohistory.com, retrieved 22 May 2020.
• Ref. 184H: "Funkortung" ["Radio direction finding"], Wilhelm Tolmé Runge, pp. 7, 8 in "Telefunken Hausmitteilungen", Telefunken, Vol. 20, Nr. 82, December 1939.
• Ref. 184J: "Air Navigation Systems: Chapter 3. The Beginnings of Directional Radio Techniques for Air Navigation, 1910–1940", in "The Journal of Navigation", Vol. 43, Issue 3, September 1990, pp. 313-330. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 184Jbis: comments to ref. 184J - "The Beginnings of Directional Radio Techniques for Air Navigation, 1910–1940" [incl. RAF air navigator RDF rules], F.C. Richardson, in "The Journal of Navigation", Volume 43, Issue 3, September 1990, pp. 441-442. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 184K: "Introduction into Theory of Direction Finding", pp. 62-85 in "Rohde & Schwarz Radiomonitoring & Radiolocation Catalog 2016", 24 pp. Retrieved 28 February 2020.
• Closely related: "An Introduction to Radio Direction Finding Methodologies", Paul Denowski, Rohde & Schwarz, 99 pp. Accessed 3 March 2020. [pdf]
• Ref. 184L: "Drahtloses Peilen" [wireless direction finding], A. Esau, pp. 3-12 in "Telefunken-Zeitung", Vol. IV, Nr. 22, March 1921. [Summary]. Source: radiomuseum.org.
• Ref. 184M: "War secrets in the ether", Wilhelm F. Flicke, translation by Ray W. Pettengill of Flicke's original German manuscript "Kriegsgeheimnisse im Aether", source: US National Security Agency (NSA), retrieved 8 March 2020.
• Part I & II (the period from the inception of the German Radio Intercept Service to the End of WW I, and the period between the two World Wars), NSA Document ID A59421, 288 pp. [pdf]
• Part III (aspects of the large scale espionage and the counterespionage (crypto, radio agents,..)), NSA Document ID A59332, 428 pp. [pdf]
• Ref. 184N: "Geschichte der Funkpeiltechnik" ["History of radio direction finding"], Rudolf Grabau, in "Funkgeschichte" (Mitteilungen der Gesellschaft der Freunde der Geschichte des Funkwesens (GFGF) e.V). [Keywords]
• Ref. 184N1: "(1) - Entwicklung der Funkpeilung bis 1945" [Development up to 1945], Vol. 28, 2005, Nr. 164, pp. 268-276. Source: www.radiomuseum.org, accessed 28 March 2020. Also docplayer.org, accessed 27 May 2021. [pdf]
• Ref. 184N2: "(2) - Entwicklung der Funkpeilung ab 1945" [Development from 1945 on], Vol. 29, 2006, Nr. 165, pp. 24-30. Source: www.radiomuseum.org, accessed 28 March 2020. Also docplayer.org, accessed 27 May 2021. [pdf]
• Ref. 184P: "Radio Direction Finding", US Army Field Manual No. 30-476, 8 April 1977, 221 pp. [file size 25 MB]
• Ref. 184Q: "Direction and Position Finding by Wireless", Ronald Keen, The Wireless Press Ltd. (publ.), 1922, 397 pp. Source: archive.org. Accessed: 6 May 2020. [Keywords: directional reception & transmission, incl. loop, cardioid, propagation]
• Ref. 184R: "Radio direction-finding and navigational aids, some reports on German work issued in 1944-45", Scientific and Industrial Research (D.S.I.R.) Radio Research Board, Special Report No. 21, 1951, 96 pp.
• 1-page review of the above document: "Radio Direction-Finding and Navigational Aids", in "Nature", Vol. 169, Nr. 4308, 24 May 1952, p. 785. Source: nature.com, retrieved 14 October 2020.
• Ref. 184S: articles about the Wullenwever RDF system
• Ref. 184S1: "Beschreibung für Großpeil- und Empfangsanlage Wullenwever Type HF 2076" ["Description of large RDF and receiver installation "Wullenwever" type HF 2076"], 11 March 1946, 27 pp. Source: cdvandt.org. Retrieved 3 February 2020.
• Ref. 184T: "The determination of the direction of arrival of short radio waves", H.T. Friss, C.B. Feldman, W.M. Sharpless, in "Proceedings of the Institute of Radio Engineers", Vol. 22, Nr. 1, January 1934, pp. 47- 78. Source: worldradiohistory.com, retrieved 21 July 2020.
• Ref. 184U: articles in "Electrical Communication - A Journal of Progress in the Telephone, Telegraph and Radio Art", published by "International Standard Electric Corp". Source: worldradiohistory.com, accessed 17 August 2020.
• Ref. 184U1: "The automatic radio compass and its application to aerial navigation", H. Busignies, in Vol. 15, No. 2, October 1936, pp. 157-172.
• Ref. 184U2: "Mountain effects and the Use of Radio Compasses and Radio Beacons for Piloting Aircraft", H. Busignies, in Vol. 19, No. 3, 1941, pp. 44-70.
• Ref. 184U3: "Evaluation of Night Errors in Aircraft Direction Finding, 150-1500 Kilocycles", H. Busignies, in Vol. 23, No. 1, March 1946, pp. 42-62.
• Ref. 184V: "Funkpeilung als alliierte Waffe gegen deutsche U-Boote 1939 - 1945: Wie Schwächen und Versäumnisse bei der Funkführung der U-Boote zum Ausgang der "Schlacht im Atlantik" beigetragen haben" [file size 74 MB], Arthur O. Bauer, Ralph Erskine, Klaus Herold, Liebich Funk GmbH (publ.), 1997, 323 pp., ISBN 3-00-002142-6. Source: cdvandt.org, retrieved 28 September 2020.
• An excerpt in English is: "HF/DF An Allied Weapon against German U-Boats 1939-1945", Arthur O. Bauer, 1998, 23 pp. Source: cdvandt.org, retrieved 28 September 2020.
• Ref. 184W: "Radio Direction Finding, 10 kc/s to 550 kc/s", Walter C. Weaver, MsEE Thesis, U.S. Naval Postgraduate School, 1957, 107 pp. Source: archive.org, retrieved 14 October 2020.
• Ref. 184X: "Direction finder and antenna research" [file size 38 MB; full resolution file is here, 242 MB], Office of Scientific Research and Development, National Defense Research Committee, Division 13 (Electrical Communication), Summary Technical Report, 1946 (declassified 1960), 292 pp. Source: loc.gov, retrieved 19 February 2021.
• Ref. 184Y: "Methods of radio direction finding as an aid to navigation: the relative advantages of locating the direction finder on shore and on shipboard", F.W. Dunmore, Dept. of Commerce, Bureau of Standards, Letter Circular No. 56 (LCIRC 56), 27 March 1922, 18 pp. Source: nist.gov, retrieved 13 April 2021.
• Ref. 184Z: "Wireless Direction Finding", C.B. Carr, in "Aircraft Engineering and Aerospace Technology", Vol. 2, Iss. 12, December 1930, pp.305-307. Source: en.booksc.org, accessed April 2021. [pdf, See note 1].
• Ref. 184AA: "Zielfluggeräte nach ‟Dieckmann-Hell‟" [Dieckmann-Hell airplane radio direction finding systems; Luftwaffe ZVG 15 / 16 / 17 Z, FuG 141], Werner Thote, in "Radiobote", Vol. 13, Nr. 76, September-October 2018, pp. 14-19. Source: radiobote.at.
• Ref. 185: radio location & navigation, general articles, articles covering multiple systems, airways, airmail
• Ref. 185A: "Survey of Radio Navigational Aids" [DF, Shoran, Oboe, DME, transponders, radar, Loran, GEE, Decca, Raydist, Micro-H, Consol, Sonne, Navaglobe, A-N ranges, CAA Omnirange, ILS landing beam, radio altimeters, rotating beacons, Orfordness range, Navar, Teleran, Navascope], Robert I. Colin, in "Electrical Communication" (Technical Journal of the International Telephone & Telegraph Corporation and Associate Companies), Vol. 24, No. 2, June 1947, pp. 219-261. Source: www.worldradiohistory.com; accessed 27 March 2020.
• Ref. 185B: "The Geography of Radionavigation and the Politics of Intangible Artifacts", William Rankin, in "Technology and Culture", Volume 55, Number 3, July 2014, pp. 622-674 [pdf]
• Ref. 185C: "Electronic Navigation Systems", Summary Technical Report of Division 13 (Electrical Communication) of the National Defense Research Committee (NDRC) - Vol. 2B, 1946, 374 pp. [file size 211 MB; a lower-but-good resolution version is here, 48 MB]. Source: US Library of Congress  www.loc.gov. Retrieved 8 August 2018. [Beacons & interrogators, Oboe, Shoran, Micro-H, DME, Gee, Loran, Decca, POPI, A-N Radio Range, ADF & homing,  Sonne/Consol (AN/FRN-5), Bendix automatic position plotter, CAA VHF Omni beacon, CAA LF Omni beacon, Federal Long-Range Navigation System, airborne radar, search radar as navigational aid, short-range approach system (AN/APN-34), radar (ground) mapping, ground-position indciator (GPI, AN/APA-44), Sperry Moni Range & Disatnce Indicator, RCA television radar system, miscellaneous German navigational systems, comparison table]
• Ref. 185C1: "Miscellaneous enemy navigational systems" [Elektra (Electra), X-System (Benito), Knickebein, (Ruffian), Hermine, Egon, Rübezahl, Bermnhard/Bernhardine, Hyperbel (Hyperbel), Truhe, Zyklop (Cyclop), Dora, Erika, Diskus, Schwanboje, Nachtfee], section 30, 6 pp.
• Ref. 185C2: "Sonne (Consol)", section 17, 26 pp.
• Ref. 185C3: "A-N Radio Range" [incl. Four-course Aural Range], Section 15, 6 pp.
• Ref. 185D: "Air Navigation", U.S. Navy Hydrographic Office H.O. Publication No. 216, corrected print 1963, 717 pp.
• Ref. 185D1: "Lines of Position, Bearings, and Fixes", Chapter IX, pp. 188-202
• Ref. 185D2: "Low Frequency Radio Range", pp. 288-300 in Chapter XI "Radio" (pp. 261-300).
• Ref. 185D3: "Hyperbolic Navigation Systems" [Loran, Decca, Lorac, Sofar, Consol, Sonne, Consolan, GEE], Chapter XIII, pp. 345-365.
• Ref. 185E: "On the origins of RF-based location", Hans Gregory Schantz, in "Proc. 2011 IEEE Radio & Wireless Symposium", Phoenix/AZ/USA 16-20 Jan., 2011. Source: researchgate.net, retrieved 16 Jan 2020.
• Ref. 185F: "Radiobeacons and radiobeacon navigation", George R. Putnam, U.S. Dept. of Commerce, Lighthouse Service, 1 July 1931, 44 pp. [pdf]
• Ref. 185G: p. 260 in "A survey of continuous-wave short-distance navigation and landing aids for aircraft", Caradoc Williams, in "Journal of the Institution of Electrical Engineers - Part IIIA: Radiocommunication", Volume 94, Issue 11, March-April 1947, pp. 255 - 266.
• Ref. 185H: "History of radio flight navigation systems - Memoirs of Dr. E. Kramar", M. Hollmann & P. Aichner (translation, ed.), 15 pp. Source: radarworld.org. [Scheller A/N, Lorenz E/T, Telefunken Knickebein, Hermes/Hermine, X-System / Wotan I, Four-Course Range, ILS, Elektra, Consol, Erika, Komet, Hohentwiel]
• Ref. 185J: magazine and journal articles in German
• Ref. 185J1: "Navigation und Luftsicherung" ["Navigation and air traffic control"], Leo Brandt, pp. 25-80 in "Arbeitsgemeinschaft für Forschung des Landes Nordrhein-Westfalen", Vol. 13, Springer Fachmedien, 1952, 98 pp. Accessed 3 March 2020. [pdf]
• Ref. 185J2: "Die Funknavigation der Luftfahrt", August Leib, in "Telefunken Hausmitteilungen", Telefunken, Vol. 20, Nr. 82, December 1939, pp. 9-68.
• Ref. 185J3: "Flugsicherung durch Richtfunkbaken" ["Radio-beacon aids to aerial navigation"], H. Rahskopff, in "Zeitschrift des Vereins deutscher Ingenieure (V.D.I.)", Vol. 75, 4 January 1931, pp. 116-117.
• Ref. 185J4: "Neuzeitliche Funknavigation - 1. Teil" ["Modern radio navigation, part 1"], W.R. Schulz,  in "Funk-Technik" (FT), "Zeitschr. für das gesamte Elektro-Radio und Musikwarenfach" (1946-49), "Fachzeitschr. für die Elektro- und Radiowirtschaft" (starting 1950), No. 8, April 1948, pp. 190-191.
• Ref. 185J5: "Neuzeitliche Funknavigation - 2. Teil" ["Modern radio navigation, part 2"], W.R. Schulz, in "Funk-Technik", No. 9, May 1948, pp. 216-217. Source: nvhrbiblio.nl, retrieved March 2021.
• Ref. 185J6: "Neuzeitliche Funknavigation - 3. Teil" ["Modern radio navigation, part 3"], W.R. Schulz, in "Funk-Technik", No. 10, May 1948, pp. 242-243. Source: nvhrbiblio.nl, retrieved May 2021.
• Ref. 185J7: "Funkbaken" ["Radio beacons"; A/N Radio Range, SBA, BABS, Eureka, Rebecca, Z, Navaglobe, VOR, ILS] W.R. Schulz, in "Funk-Technik", Nr. 1, January 1950, pp. 10, 11. Source: nvhrbiblio.nl, retrieved March 2021.
• Ref. 185K:
• Ref. 185K1: "Radio in navigation" [Part 1], C.D. Tuska, in "Journal of the Franklin Institute", Vol. 228, Iss. 4, October 1939, pp. 433-443. Source: en.booksc.org, retrieved 20 April 2021 [pdf, See note 1]
• Ref. 185K2: "Radio in navigation" [Part 2], C.D. Tuska, in "Journal of the Franklin Institute", Vol. 228, Iss. 5, November 1939, pp. 581-603. Source: en.booksc.org, retrieved 20 April 2021 [pdf, See note 1]
• Ref. 185L: "A Brief Description of the Major Second World War Navigational Aids", Brian Kendal, in "Journal of Navigation", Vol. 45, No 1, Januay 1992, pp. 70 - 79. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 185M: "Highlights of antenna history", Jack Ramsay, in "IEEE Communications Magazine", Vol. 19, Iss. 5, September 1981, pp. 4-16. Accessed 6 May 2020. [pdf]
• Ref. 185N: "A review of radio aids in aviation" [DF, Radio Ranges, homing, hyperbolic, Gee, Loran, Decca, Lorenz BAS, VHF/UHF ILS], C.B. Bovill, in "The Journal of the British Institution of Radio Engineers", Vol. VI, Nr. 6, December 1946, pp. 250-272. Source: delibra.bg.polsl.pl, retrieved 20 April 2021.
• Ref. 185P: "Radio navigation in the 1920s" [abstract], C. Powell, in "Journal of the Institution of Electronic and Radio Engineers (IERE)", Vol. 56, Nr. 8-9, August/September 1986, pp. 293-297. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 185Q: "La Radionavigation" [in French], J. Piergo, pp. 159-167 in "Science et Vie", No. 349, October 1946.
• Ref. 185R: "The Aeronautical Navigational Radio Service" [Keywords: Consol, Decca, Loran, GEE, SBA, BABS, MF Range], Chapter VII (pp. 101-109) in "The Civil Aviation Communications Handbook", Vol. 5 of CAP series (M.C.A.P.5), Great Britain Ministry of Civil Aviation, 2^nd ed., 1949, 286 pp. Source: atchistory.files.wp.com. Accessed 19 May 2020. [pdf, file size 26 MB]
• Ref. 185S: "RF Positioning - Fundamentals, Applications, and Tools" [Keywords: RDF, TFK Kompass, Orefordness, Sonne, Gee, Oboe, Gee-H, Loran], Rafael Saraiva Campos, Lisandro Lovisolo, Artech House (publ.), 29 pp. Accessed: 31 January 2020. [pdf]
• Ref. 185T: articles about airmail and airlines
• Ref. 185T1: "Mail Planes Radio Equipment", in "Radio Topics", March 1924, pp. 15-16. Source: worldradiohistory.org, accessed 14 April 2020.
• Ref. 185T2: "Airlines and Air Mail - The Post Office and the birth of the commercial aviation industry", F. Robert van der Linden, The University Press of Kentucky, 2002, 367 pp. Source: core.ac.uk, retrieved 12 February 2021 [file size: 25 MB]
• Ref. 185T3: "Airmail: A Brief History", United States Postal Service, March 2018, 7 pp. Source: usps.com, retrieved 21 October 2020.
• Ref. 185U: "A radio-acoustic method of locating positions at sea: Application to navigation and to hydrographical survey", A.B. Wood, H.E. Browne, in "Proc. of the Physical Society of London", Vol. 35, Part ???, No. 1, 15 April 1923, pp. 183-193. Source: en.booksc.org, accessed 27 May 2021. [pdf, See note 1]
• Ref. 185V: "Aerodrome and Air Route Control", in "The Marconi Review", No. 65, March-April 1937, pp. 9-19. Source: worldradiohistory.com, retrieved 20 April 2021.
• Ref. 185W: "Navigation by cigars" [orig. published in a Pittsburgh newspaper on 19 May, 1938], on p. 47 in "A Place in the Sky: A History of the Arnold Palmer Regional Airport, 1919-2001", Richard David Wissolik (gen. ed.), Saint Vincent College for Northern Appalachian Studies (publ.), 2001, ISBN-13: 978-1885851178, 225 pp.
• Ref. 185X: publications about aviation/flight navigation in general
• Ref. 185X1: "Flight Navigator Handbook", US Dept. of Transportation, Federal Aviation Administration, publication FAA-H-8083-18, 2011, 281 pp.
• Ref. 185Y: articles  in "The Journal of Navigation"
• Ref. 185Y1: "Air Navigation Systems: Chapter I. Astronomical Navigation in the Air 1919–1969", J.E.D. Williams, in "The Journal of Navigation", Vol. 41 , Issue 3, September 1988, pp. 375-406. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 185Y2: "Air Navigation Systems: Chapter I. Astronomical Navigation in the Air 1919–1969. Part II - Instruments", J.E.D. Williams, in "The Journal of Navigation", Vol. 42 , Issue 1, January 1989, pp. 73-91. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 185Y3A: "The beginnings of air radio navigation and communication", Brian Kendal, in "The Journal of Navigation", Vol. 64, Iss. 1, January 2011, pp. 157-167.. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]]
• Ref. 185Y4B: response to ref. 185Y3A - "The beginnings of air radio navigation and communication", Walter Blanchard, in "The Journal of Navigation", Vol. 64, Iss. 3, July 2011, pp. 571-572. Source: en.booksc.org, accessed 27 May 2021. [pdf, See note 1]
• Ref. 185Z: articles by Robert Watson-Watt
• Ref. 185Z1: "Radio Aids to Navigation", Robert Watson-Watt, in "The Journal of Navigation", Vol. 1, Iss. 1, January 1948, pp. 15-21. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 185Z2: "The evolution of radiolocation" [incl. Oboe, Rebecca-Eureka, Orefordness, G-H, BABS], Robert Watson-Watt, in "Journal of the Institution of Electrical Engineers - Part I: General", Vol. 93, Iss. 69, September 1946, pp. 374-382 Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 186: Transmitter technology - spark gap, arc converter, machine generator, vacuum tube (incl. micro wave)
• Ref. 186A: pp. 420-423 in "Handbuch der drahtlosen Telegraphie und Telephonie - Ein Lehr- und Nachschlagebuch der drahtlosen Nachrichtenübermittlung" ["Handbook of wireless telegraphy and telephony - a textbook and reference book of wireless communication"] , Vol. 1, Eugen Nesper, Julius Springer (publ.), 1921, 708 pp. Source: archive.org, accessed 30 March 2020. [pdf; file size: 65 MB]
• Ref. 186B: "Die »Tönenden Funken« - Geschichte eines frühen, drahtlosen Kommunikationssystems, 1905-1914" ["Tonal quenched spark gap transmission - history of an early wireless communication system"], Michael Friedewald, Vol. 2 of "Aachener Beiträge zur Wissenschafts- und Technikgeschichte des 20. Jahrhunderts", Verlag für Geschichte der Naturwissenschaften und der Technik (GNT-Verlag, publ.), 1999, 185 pp., ISBN 978-3-928186-38-4. [Table of contents and review]
• Ref. 186C: "Über die Intensität der beiden Schwingungen eines gekoppelten Senders" ["About the intensity of both types of oscillations of a coupled transmitter"; quenched-spark transmitter], Max Wien, in "Physikalische zeitschrift", Vol. 7, Nr. 23, 15 November 1906, pp. 871-872.
• Ref. 186D: "Beschreibung der kommerziellen Land-Schiff-Station Telefunken Type 0,5 T.K. 0,5 KW Antennen-Schwingungsenergie bei 1,5 KW Primärenergie" ["Description of the Telefunken commercial land/ship-board transmitter model 0,5 T.K. 0.5 kW output power for 1.5 kW dissipation"], 1916 Telefunken brochure (transcribed and adapted by Heinrich Busch, 2016). Source: seefunknetz.de, accessed 3 April 2020. [pdf]
• Ref. 186E: "The Spark Transmitter", "Section "A", 27 pp, in "Wireless telegraphy Theory", Vol. II of "Admiralty Handbook of Wireless Telegraphy", H.M. Signal School, 1938, 1943 revised ed. , B.R.230, 530 pp. Accessed 15 April 2019. [pdf]
• Ref. 186F: "Die technische Entwicklung der Verschiedenen F.T.-Systeme" ["The technical development of various spark transmitter systems"; Poulsen, Wien, HF machine-generators], pp. 3-6 in "Funkentelegraphie für Flugzeuge" [Spark gap telegraphy for aircraft], Erich Niemann, Vol. IX of "Handbuch der Flugzeugkunde", Richard Carl Schmidt & Co. (publ.), 1921, 434 pp. Source: archive.org, accessed 15 April 2020. [pdf]
• Ref. 186G: "Wireless telegraphy", Jonathan Zenneck, McGraw-Hill Book Co. (publ.), 5^th ed., 1918, 443 pp. [pdf; file size: 360 MB]; translation of the German original "Lehrbuch der drahtlosen Telegraphie", Jonathan Zenneck, F. Enke (publ.), 1913, 521 pp.
• Ref. 186G1: Chapter VII: "Transmitters of damped oscillation" [Marconi, Braun, Wien, stationary & rotating electrodes, quenched], pp. 173-212. [file size: 35 MB]
• Ref. 186G2: Chapter VIII: "High frequency machines for undamped oscillations" [Fessenden, Alexanderson, C. Lorenz Co., Goldschmidt, Eberswalde], pp. 213-219.
• Ref. 186G3: Chapter IX: "Undamped oscillations by the arc method" [Poulsen], pp. 220-245. [file size: 21 MB]
• Ref. 186G4: §207 "The advantages of directive signalling" [incl. Telefunken Compass], pp. 365-370.
• Ref. 186H: §8 of Article 5 (pp. 36-37), §1 & §3 of Article 16 (p. 74-76) in International Telegraph Convention 1927 - Treaties, Washington/DC/USA, 1927, 171 pp. Source: International Telecommunication Union, accessed 29 April 2020.
• Ref. 186J: "Zusammenstellung der modernsten tönenden und ungedämpften Radio-Stationen und -Geräte" ["Overview of the most modern quenched spark and undamped (continuous wave) radio sets and equipment"], Telefunken Gesell. für drahtlose Telegraphie m.b.H., product catalog, November 2020 (product status of early 1919), 244 pp. [file size: 32 MB]. Source: www.cdvandt.org. Accessed 1 May 2020.
• Ref. 186J1: Chapter 2, Group II: "Gruppe II. Land- und Schiffs-Stationen" ["Group II, Land and shipstations"], 30 pp. [singing spark transmitter models 0,2 TK; 0,5 TK; Debeg-Schrank-Station; 1,5 TK; 2,5 TK; 5 TK; 7,5 TK; 10 TK; 15 TK; 25 TK; 35 TK; 0,4 TV Behelfs-Station; 0,5 TV; 1 TV; 2 TV; 2,5 TV; 4 TV; 10 TV; all of these spark transmitter models appear to have alreday been marketed by mid-1913; continuous wave vacuum tube transmitter models 0,5 kW; 1 kW, 5 kW].
• Ref. 186J2: Chapter 2, Group III: "Gruppe III. Flugzeug- und Luftschiffstationen" ["Group III, Aeroplane and airship stations"], 16 pp. [AFS 35; Sender-Empfänger A, D4, G, N, R, ALS 49; Röhren-Sender-Empfänger ARS 80a; Empänger E; Dynamo Maschine B, C, D16, D17, G, R, RS, TL 3,5/20]
• Ref. 186K: "Funkentelegraphie und -telephonie mit ungedämpften Schwingungen" ["Spark gap telegraphy and telephony with undamped waves"], Rudolf Grabau, in "Funkgeschichte", Vol. 29, Nr. 168, 2006, pp. 177-185. Accessed 19 April 2020. [pdf]
• Ref. 186L: "Elektromagnetische Schwingungen und Drahtlose Telegraphie" ["Electromagnetic oscillations and wireless telegraphy"], Jonathan Zenneck, Ferdinand Enke (publ.), 1905, 1056 pp. Source: us.archive.org, accessed 19 April 2020.
• Ref. 186M: "Sendeprinzipien" ["Principles of radio transmitters"], pp. 332-335 in "Radios von gestern: Das Sachbuch für Sammler und Radio-Amateure", Ernst Erb, 3^rd ed., 1998, 456 pp. Source: radiomuseum.org, accessed 19 April 2020 [pdf]
• Ref. 186N: "Historical remarks to the history of electrical oscillators", Wolfgang Mathis, in "Proc. of the International Symp. on Mathematical Theory of Networks and Systems (MTNS)", Padua/Italy, 1998, 4 pp. Source: www.researchgate.net. Accessed 1 May 2020.
• Ref. 186P: "Die Technik der Funkentelegraphie mit gedämpften Schwingungen", ["Spark gap telegraphy and telephony with damped waves"], Rudolf Grabau, in "Funkgeschichte", Vol. 29, Nr. 167, 2006, pp. 136-147. Source: radiomuseum.org, accessed 19 April 2020. [pdf]
• Ref. 186Q: articles by and about Karl Ferdinand Braun
• Ref. 186Q1: "Notizen über drahtlose Telegraphie" ["Notes on wireless telegraphy"], Ferdinand Braun, in "Physikalische Zeitschrift", Vol. 4, Nr. 13, 1 April 1903, p. 361-364. Provides §1 "Zur Beseitigung eines Missverständnisses. Einige historische Bemerkiungen" ["Clearing up of a misunderstanding. Some historical comments"] with brief overview of transmitter technology of those days (Hertz, Marconi, Righi oscillator, spark gap, Slaby, Ascoli, Abraham, antenna reflector), and §2 "Versuche über eine Art gerichteter Telegraphie" ["Tests with a form of directive telegraphy]).
• Ref. 186Q2: "Ferdinand Braun - A Pioneer in Wireless Technology and Electronics", Peter Russer, pp. 228-247 in Section III of "A Wireless World. One Hundred Years since the Nobel Prize to Guglielmo Marconi", Firenze University Press (publ.), first edition, 2012, 370 pp. Source: researchgate.net, retrieved 1 May 201.
• Ref. 186Q3: "Electrical oscillations and wireless telegraphy", Karl Ferdinand Braun, 1909 Nobel Prize in Physics acceptance lecture, Stockholm, December 1909. Source: nobelprize.org, retrieved 3 May 2021.
• Ref. 186R: "Klystrons, Traveling Wave Tubes, Magnetrons, Crossed-field Amplifiers, and Gyrotrons", A. S. Gilmour, Artech House (publ.), February 2011, 864 pp., ISBN 9781608071845.
• Ref. 186S: "The Magnetron", Albert W. Hull, in "Journal of the American Institute of Electrical Engineers", Vol. XL, Nr. 9, September 1921, pp. 715-723. Source: hathitrust.org, retrieved 17 April 2021.
• Ref. 186T: "The Cavity Magnetron: not just a British invention", Yves Blanchard, Gaspare Galati, Piet van Genderen, in "IEEE Antennas and Propagation Magazine", Vol. 55, No. 5, October 2013, pp. 244-254. Source: ieeexplore.ieee.org, accessed 26 April 2021. [pdf, See note 1]
• Ref. 186V: "The Marconi timed-spark continuous-wave transmitter", Philip R. Coursey, in "The Wireless World", Vol. VII, No. 78, September 1919, pp. 310-316. Source: worldradiohistory.com, retrieved 3 May 2021.
• Ref. 186W: "Fessenden and the early history of radio science", John S. Belrose, in "Proceedings of the Radio Club of America", Vol. 67, Nr. 2, November 1993, pp. 6-23. Source: worldradiohistory.com, retrieved 1 April 2021.
• Ref. 186X: "Half a century since the wireless world began", A.D. Blumlein, in "The Wireless World", Vol. 67, No. 4, April 1961, pp. 155-183. Source: worldradiohistory.com, retrieved 3 May 2021.
• Ref. 186Y: multiple articles about WW1 Telefunken's spark transmitter and U-boat radio technology in "Telefunken-Zeitung, Zweite Kriegsnummer, Vol. III, Nr. 16, July 1919". Source: radiomuseum.org, accessed 28 May 2021. [pdf]
• Ref. 186Z: pp. 259, 260 in "Father of Radio: The autobiography of Lee de Forest", Lee de Forest, Wilcox & Follet Co. (publ.), 1950, 502 pp. Source: worldradiohistory.com, accessed October 2022.
• Ref. 187: Telefunken Compass
• Ref. 187A: articles about the German Fog Signal Service and the "Seezeichenversuchsfeld" (Maritime Navigation Markers Test Site)
• Ref. 187A1: "Elektrische Wellen im Nebelsignaldienst" ["Electrical waves in the Fog Signal Service"], Walter Körte, pp. 570-571 in "Zentralblatt der Bauverwaltung", Nr. 87, 30 October 1909. Source: digital.zlb.de. Retrieved February 2020.
• Ref. 187A2: "Die Entwicklung des deutschen Seezeichen-Versuchswesens" ["The development of the German maritime signalling research institute"], Breuer, in "Zentralblatt der Bauverwaltung", Vol. 50, Nr. 1, 8 January 1930, pp. 44–46. Source: digital.zlb.de. Retrieved 17 April 2020.
• Ref. 187A3: "Das Seezeichen-Versuchsfeld des Reichsverkerhsministeriums in Berlin-Friedrichshagen" ["The maritime signalling test site of the Ministry of Transport in Berlin-Friedrichshafen], Breuer, in "Zentralblatt der Bauverwaltung", Vol. 50, Nr. 25, 25 June 1930, pp. 452-457, and Nr. 26, 2 July 1930, pp. 467-471. Source: digital.zlb.de. Retrieved 17 April 2020.
• Ref. 187A4: "Nautischer Verein zu Bremen" ["The Nautical Association in Bremen"], in "HANSA, Deutsche Nautische Zeitschrift", Vol. 50, No. 49, 6 December 1913, p. 1034. Source: digishelf.de. Retrieved 16 April 2020.
• Ref. 187A5: "Funknavigation (Seefunkfeuer) - Arbeiten der preußischen und deutschen Seezeichen Verwaltung und des Seezeichenversuchsfeld - Eine Zusammenfassung der Entwicklungsgeschichte der funktechnischen Seezeichen aus Akten von 1905 - 1939; Teil 1 (1905 - 1910)", Johannes Braun, 1962. Source: web.archive.org (part 2 not available). Retrieved 17 April 2020.
• Ref. 187A6: "Geheimer Oberbaurat Körte" ["Privvy Counsel Körte"], Roloff, in "Zentralblatt der Bauverwaltung", Vol. 34, Nr. 39, 16 May 1914, pp. 297-298. Source: digital.zlb.de. Retrieved 17 April 2020.
• Ref. 187A7: "Die Versuche der deutschen Verwaltung mit elektrischen Wellen im Nebelsignaldienst (Funkfeuer / Seefunkfeuer)" ["Experiments by the Authorities with electrical waves in the Fog Signal Service (radio beacons / maritime radio beacons)"], Johannes Braun, Fachstelle der WSV für Verkehrstechnik (publ.), Koblenz 1962. [Summary]. Retrieved in part from web.archive.org on 25 February 2020
• Ref. 187B: p. 3 in "Telefunken und der deutsche Schiffsfunk, 1903 - 1914" ["Telefunken and German marine radio"], Michael Friedewald, in "Zeitschrift für Unternehmensgeschichte", Vol. 46, Issue 1, April 2001, pp. 27-57. Retrieved 19 April 2020. [pdf]
• Ref. 187C: Telefunken-Kompass; 3 near-identical Telefunken articles. [Summary]
• Ref. 187C1: "Telefunken-Kompass", in "Dinglers Polytechnisches Journal", Year 93, Vol. 327, No. 34, 24 August 1912, pp. 538–541. Source: DFG Digitalisierung des Polytechnischen Journals (Creative Commons 3.0 license).
• Ref. 187C2: "Telefunken-Kompass", pp. 77-84 in "Telefunken Zeitung", Vol. 1, Nr. 5, April 1912. Source: radiomuseum.org.
• Ref. 187C3: "Telefunken Kompass", in "Jahrbuch der drahtlosen Telegraphie und Telephonie sowie des Gesamtgebietes der elektromagnetischen Schwingungen", Nr. 1, July 1912, pp. 85-92, Nr, 2, September 1912, p. 198.
• Ref. 187D: "Telefunken-Kompaß", pp. 15 & 17 in "Telefunken Zeitung", Vol. 2, Nr. 7, August 1912. Source: radiomuseum.org.
• Ref. 187E: articles from the "Popular Science Monthly" magazine.
• Ref. 187E1: "Safeguarding Vessels by Radio" [Bellini-Tosi directional receiver, Telefunken Compass], Annis Salsbury, in "Popular Science Monthly", Vol. 88 [file size: 92 MB], No. 3, March 1916, pp. 451-453. Retrieved 15 April 2020.
• Ref. 187E2: "How the Zeppelin Raiders Are Guided by Radio Signals", in "Popular Science Monthly, Vol. 92" [file size: 92 MB], No. 4, April 1918, pp. 632-634. Retrieved 27 February 2020.
• Ref. 187F: "50 Jahre Telefunken - Festschrift zum 50 jährigen Jubileum der Telefunken Gesellschaft für drahtlose Telegraphy m.b.h. - Gleichzeitig als 100. Ausgabe der Telefunken Zeitung", Vol. 26, Nr. 100, May 1953, 164 pp. Source: nvhrbiblio.nl, retrieved 19 February 2020.
• Ref. 187F1: "Die Zeit des Funkensenders" [The era of the spark gap transmitters], J. Zenneck, pp. 153-158.
• Ref. 187F2: "Fernsehen, Richtstrecken und Funkortung" [Television, directional microwave links, and radio D/F], W.T. Runge, pp. 181-190.
• Ref. 187G: "Meißner, Alexander (Meissner)", pp. 92-93 in "Biografien österreichischer Physiker - Eine Auswahl", D. Angetter, M. Martischnig, Österreichisches Staatarchiv, 2005, 175 pp.
• Ref. 187H: "Orientierung von Luftschiffen" ["Airship navigation"], pp. 110, 111, 114 in "Telefunken Zeitung", Vol. 2, Nr. 11, April 1913. Source: radiomuseum.org.
• Ref. 187J: "Der Peilsender Kleve der Kaiserlichen Marine in Hau" ["The directional beacon (Telefunken Compass station) of the Imperial Navy at Kleve/Hau", Bernd-Rüdiger Ahlbrecht, pp. 20-24 in "Geschichtsbrief Bedburg-Hau", Nr. 14, 2019, Geschichtsverein Bedburg-Hau e.V. (publ.),72 pp. Accessed 15 April 2019.
• Ref. 187K: p. 71 in "Die Antenne - Zeitschrift für drahtlose Nachrichtenübermittlung und verwandte Gebiete", Dr. Erich F. Huth G.m.b.H. – Gesellschaft für Funkentelegraphie (publ.), Vol. 2, Nr. 4, July 1913. Source: de.wikipedia.org.
• The same image is also used on p. 408 of "Das deutsche Seezeichenwesen – 1850–1990 zwischen Segel- und Container-Schiffsverkehr", Gerhard Wiedemann (ed.), Johannes Braun, Hans Joachim Haase, DSV Verlag (publ.), Hamburg 1998, 640 pp.
• Ref. 187L: "Meißner, Alexander, Funkingenieur" [radio engineer], 3-page bio, pp. 695-697 in "Maly - Melanchton", Vol. 16 of "Neue deutsche Biographie", Otto zu Stolberg-Wernigerode (ed.), Duncker & Humblot (publ.), 1990, 785 pp. Accessed 16 April 2020.
• Ref. 187M: "Telefunken auf der Allgemeinen Luftschiff-Ausstellung (Ala)", pp. 53-56 in "Telefunken Zeitung", Vol. 1, Nr. 5, April 1912. Source: radiomuseum.org. [pdf].
• Ref. 187N: "The Radio Direction Finder", Chapter XXII (pp. 261-265) in "History of Communications-Electronics in the United States Navy", Linwood S. Howeth, Bureau of Ships and Office of Naval History, 1963, 698 pp. Source: hathitrust.org, retrieved May 2020.
• Ref. 187P: Appendix A3 (pp. 33-43) in "Fire Island Lighthouse and Keeper's Dwelling", Vol. 3 of "Historic Structure Report", 470 pp. Source: US National Archives and Records Service. [file size: 37 MB]. Retrieved 2 May 2020.
• Ref. 187Q: articles [in Dutch] in "Radio-Nieuws - Maandblad van de Nederlandsche Vereeniging voor Radiotelegrafie". Source: nvhrbiblio.nl. Accessed: 13 April 2020.
• Ref. 187Q1: "Een geheimzinnig station" ["A mysterious station"], Vol. 1, No. 3, 1 March 1918, p. 40.
• Ref. 187Q2: "Geheimzinnige stations" ["Mysterious stations"], Vol. 1, No. 4, 1 April 1918, pp. 82-84.
• Ref. 187Q3: "De A. B. C. stations" ["The A.B.C. stations"], Vol. 1, No. 5, 1 May 1918, pp. 89-90.
• Ref. 187Q4: "De B.C.-stations" ["The B.C.-stations"], Vol. 1, No. 6, 1 June 1918, pp. 125-128.
• Ref. 187Q5: "Nog eens het CCC-station" ["Once more, the CCC-station], Vol. 2, No. 2, 1 February 1919, pp. 33-35.
• Ref. 187Q6: "Is het toch Kleef geweest?" ["Was it Cleves after all?"], Vol. 2, No. 3, 1 March 1919, pp. 70-71.
• Ref. 187Q7: "Nog eens het CCC-station" ["Once more, the CCC-station"], Vol. 2, No. 3, 1 March 1919, pp. 71-73.
• Ref. 187Q8: "Weer het CCC-station" ["Again, the CCC-station"], Vol. 2, No. 4, 1 April 1919, pp. 115.
• Ref. 187Q9: "Het b-station" ["The b-station"], Vol. 2, No. 12, 1 December 1919, p. 405-409.
• Ref. 187R: "Die Richtungssendeanlagen Cleve und Tondern" ["The directional transmitting stations Cleve and Tondern"], pp. 961-964 in "Die Funkpeilung", Leo Pungs, F. Banneitz, Section 3 of Chapter VI of Part 5 in "Taschenbuch der drahtlosen Telegraphie und Telephonie", Vol. 1, F. Banneitz (ed.), Springer-Verlag (publ.), 1927, 1254 pp.
• Ref. 188: List of 1929-1940 patents of the Conz company (and its employees) regarding frequency conversion and motor speed control; source: DEPATISnet (search-engine of the German patent & trademark office, DPMA).
• Ref. 197: pp. 11-13, 24 in "Kabel-Herstellung: Kabelaufbau, Werkstoffe, Verfahrenstechnik" [cable manufacturing], Walther Ehlers, Hermann Lau, Springer-Verlag (publ.), 1956, 434 pp.
• Ref. 208: carbon pile regulators:
• Ref. 208A: "Carbon Pile Regulator" pp. 11-13 in "Aircraft Electrical Systems", E.H.J. Pallett, Pitmann Publ., 1976, 166 pp.
• Ref. 208B: "Carbon pile regulators", June 1945 [pdf]
• Ref. 208C: Pintsch advertising, p. II  in "Elektrotechnische Zeitung", Nr. 12 (21 March), 1935
• Ref. 210: Maps (charts) with Luftnachrichten Anlagen (Luftwaffe Signal Corps installations) from the Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016". Note: at the Archive, only free-hand photography is allowed (no tripod, etc.), under sub-obtimal lighting conditions. Also, most of the oprational maps are large, folded into A4-size (ca. 21x30 cm, ≈8x12 inch), and are not flat when unfolded...
• Ref. 210A: "Funk-Navigationsanlagen im Reichsgebiet" (radio-navigation stations in the Reich), Oberkommando der Luftwaffe [OKL] - Generalnachrichtenführer 1- II. Map is dated 15 June 1944. [file size: 65 MB; good-but-lower-resolution file is here 12 MB]. Source: BArch-MA/BAMA file nr. (Signatur) RL 2-V/8 "Ln. Anlagen (Karten)", Bandnr. 2, Teil 2 of "Anlage B, Teil 2: Ln. Anlagen verschiedener Art, Juni - Aug. 1944".
• Bernhard stations Be-0, Be-9, B-10, Be-11, and Be-12 are marked on this map. Map size 4x5 A4-size panels.
• Ref. 210B: "Bernhard"-Anlagen im Reichsgebiet"(radio-navigation stations in the Reich), OKL - Generalnachrichtenführer Abt. 1/ II. Map is dated 1 July 1944.  [file size: 24 MB]. Source: BArch-MA/BAMA file nr. (Signatur) RL 2-V/8.
• Bernhard stations Be-0, Be-6, Be-8 through Be-12, and Be-14 through Be-16 are marked on this map. Map size 5x2½ A4-size panels.
• Ref. 210C: "Ln.-Anlagen Westfront" (Luftwaffe Signal Corps installations on the western front). Map is dated 30 August 1944. [file size: 22 MB]. Source: BArch-MA/BAMA file nr. (Signatur) RL 2-V/8
• Bernhard station Be-6 is marked on this map. Map size 4x3 A4-size panels.
• Ref. 210D: "Funk-Navigationsanlagen Ost-Raum" (radio-navigation installations, eastern area), OKL Generalnachrichtenführer 1. Abt.II. Map is dated 15 June 1944. [file size: 44 MB; good-but-lower-resolution file is here, 26 MB]. Source: BArch-MA/BAMA file nr. (Signatur) RL 2-V/8.
• Map is marked with locations of Sonne, Komet, Zyklop, Egon, and Truhe stations. Map size 5x5 A4-size panels.
• Ref. 210E: "Funk-Navigationsanlagen Westraum" (radio-navigation installations, western area), OKL - Generalnachrichtenführer 1. Abt. II. Map is dated 15 June 1944. [file size: 83 MB; good-but-lower-resolution file is here, 10 MB]. Source: BArch-MA/BAMA file nr. (Signatur) RL 2-V/8.
• Bernhard stations Be-2, Be-6, Be-8, and Be-10 are marked on this map. Map is marked with locations of Sonne, Knickebein, Komet, Zyklop, Bernhard, Truhe, Erika, Y-(Kampf), Egon (Kampf), Baldur, Peildörfer, Flugsicherungshaupstellen, and Flugsichsrungszentralen.
• Map size 6x5 A4-sheets (WxH). Map scale is 1:2000000.
• Ref. 210F: "Funknavigationsanlagen" (radio-navigation installations), OKL - Generalnachrichtenführer 1. Abt.II Map is dated 1 October 1944. [file size: 107 MB; good-but-lower-resolution file is here, 13 MB]. Source: BArch-MA/BAMA file nr. (Signatur) RL 2-V/13.
• Map covers Europe, from mid-Scandinavia down to mid-Italy. Map is marked with locations of Sonne, Zyklop, Egon, Truhe, Bernhard, Y-Kampf, Hermes/Hermine, Knickebein, Komet, Erika, Flugsicherungs-Zentralen, Flugsicherungshauptstellen. Map size 7x4 A4-sheets (WxH). Map scale 1:200000.
• Ref. 210G: "Flughafen-Bereichskommando (Koflug) 10/XII". Map is not dated. Source: BArch-MA/BAMA file nr. (Signatur) RL 20/310.
• Koflug 10/XII moved to Morlaix/Bretagne in July of 1940; it was dissolved in October of 1944.
• Bernhard station Be-2 is marked on this map. Map is marked up with Korps- & Divisions-boundaries, Ln.-Anlagen, Flugwachen, Fliegerhorste, Unterstellungen, Armeekorps LXXIV & XXV; map scale 1:500000.
• Ref. 210H: "Kommando des Flughafenbereiches 8/XII (Morlaix)" (Kdo FHB 8-XII). Map is dated 6 July 1944. [file size: 91 MB; good-but-lower-resolution file is here, 31 MB]. Source: BArch-MA/BAMA file nr. (Signatur) RL 20/310.
• Bernhard station Be-2 is marked on this map. Map covers the western half of Brittany (Bretagne). Map is marked with boundaries at Ln. Korps & Division level; Map scale 1:200000.
• The original large single-sheet map (ca. 120x105 cm overall size) was divided into 4x5 separate map panels of ca. A4 size, that were glued onto a large sheet of thin gray canvas, and folded.
• Ref. 210J: Map of FuMG Stellungen in Litauen [Luftwaffe radar sites in Lithuania], Oberkommando der Luftwaffe - Generalnachrichtenführer (O.K.L. Gen.Nafü), 1. Abt. (III). Map is dated 21 July 1944. Source: BArch-MA/BAMA file nr. (Signatur) RL 2-V/6.
• Flugwachkommandos, Flugmeldezentralen, Luftflottengrenzen also marked on the map. Map scale 1:2500000, Zchs.Nr. 44/46.
• Ref. 210K: Map "Ln. Anlagen im Raume Rumänien" (Luftwaffe Signal Corps installations in Rumania]). Map is dated 25 August 1944. [file size: 25 MB].  Source:  BArch-MA/BAMA file nr. (Signatur)  RL 2-V/8.
• Map is marked with locations of FuMG, Funknav. Anlagen, LVerm., Jägerleistellungen. Map size 5x2 A4-sheets (WxH).
• Ref. 210L: Map "Ln. Anlagen im Raume Bulgarien" (Luftwaffe Signal Corps installations in Bulgaria). Map is dated 25 August 1944. [file size: 21 MB].  Source: BArch-MA/BAMA file nr. (Signatur) RL 2-V/8.
• Map is marked with locations of FuMG, Funknav. Anlagen, LVerm., Flugsicherungshaupstellen, Jägerleistellungen. Also, 1 map panel has listing of Luftnachrichtentruppe units present in Bulgaria at that time. Map size 5x2 A4-sheets (WxH).
• Ref. 210M: "Ln.-Anlagen im Raume Finnland - Übersichtskarte von Nord-Finnland" (Luftwaffe Signal Corps installations in Finland). [file size: 34 MB; good-but-lower-resolution file is here, 4 MB]. Map is dated 14 October 1944. Source: BArch-MA/BAMA file nr. (Signatur) RL 2-V/13/K5.
• Map is marked with locations of FuMG, Funknav. Anlagen Sonne, Kzw-Adcock, Luftparke, FMZ, S.u.J.-Stellen, Frontrep. Betriebe, LVerm., Flugsicherungshaupstellen, and Jägerdienste. Map markings include dates of explosive destruction or disassembly ("Sprengung", "Abbau"). Map size 3x2½ A4-sheets (WxH).
• Ref. 210N: "Untitled map of northernmost Scandinavia". Map is not dated. Source: BArch-MA/BAMA file nr. (Signatur) RL 2-V/13.
• Map is marked with location of "Sonne" beacons S-20 at Andö and S-17 at Svanvik, Flugsicherungszentralen "Lofoten", "Polarmeer", nr. 11 at Kemi/Finland. Map scale 1:4000000. Map size 2x1 A4-sheets (WxH).
• Ref. 210P: "Ln.-Anlagen Baltikum" (Luftwaffe Signal Corps installations in the Baltic area). Map is dated 18 September 1944. [file size: 24 MB; good-but-lower-resolution file is here, 3 MB]. Source: BArch-MA/BAMA file nr. (Signatur) RL 2-V/13/K3.
• Map is marked with locations of FuM, LV, and RV-Netz. Map size 2x2 A4-sheets (WxH).
• Ref. 210Q: "Ln. Anlagen im Raume Griechenland" (Luftwaffe Signal Corps installations in Greece). Map is dated 30 August 1944 - 5 November 1944 [file size: 26 MB; good-but-lower-resolution file is here, 4 MB].
• Map is marked with locations of FuMG, Flugsicherungszentralen, L. Verm., Luftparke, Ln. Gast., Frontrep. Betr., Rep. & Sammelstellen f. Bordfunk Geräte. Map size 4x2 (WxH) A4-sheets. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) RL 2-V/13.
• Ref. 210R: Map "Drahtlage Ost" (wired communication links, eastern area). Map is not dated. [file size: 21 MB]. Source: BArch-MA/BAMA file nr. (Signatur RL 2-V/8.
• Map is marked with line types (DK, Zuspannung, Heereslinie, Fernkabel, I-Kabel, LF-Kabel), LV, Schaltstellen. Scale 1:2500000.
• Ref. 210S: "I. Flugsicherungsbezirke" (air traffic control districts), OKL. Gen.-Nafü, 1. Abt. II. Map is dated 1 October 1944. [file size: 91 MB; good-but-lower-resolution file is is here, 11 MB]. Source: BArch-MA/BAMA file nr. (Signatur) RL 2-V/13.
• Colored map covers area of the southern half of Scandinavia through Greece. A seperate smal map of entire Scandinavia is attached to the back of the map (included). Map is marked with locations of Flugsicherungszentralen, Flugsicherungshauptstellen. Map scale 1:200000. Map size 5x4 (WxH) A4-sheets.
• Ref. 210T: "I. Flugsicherungsbezirke" (air traffic control districts). Map is dated 1 October 1944. [file size: 17 MB; good-but-lower-resolution file is here, 2 MB].  Source: BArch-MA/BAMA file nr. (Signatur) RL 2-V/13.
• Black & white map covers area of the southern half of Scandinavia through Greece. Map is marked with locations of Flugsicherungs-Hauptstellen and Flugsicherungszentralen. Map size: 3x2 (WxH) A4-sheets.
• Ref. 210U: "Wassermann-Einsatz und -Planung" (operational and planned Wasserman sites), Zeichgs-Nr. 44/18-1-A, GKdos, OKL. Gen.-Nafü, 1. Abt. III. Map is dated 20 June 1944. [file size: 76 MB; good-but-lower-resolution file is here, 8 MB]. Source: BArch-MA/BAMA file nr. (Signatur) RL 2-V/9.
• Map covers area of northern Britain to northwestern Egypt. Map is marked with locations of Wassermann (L/M/S; operational/under construction/planned by Luftflotten, proposed by O.K.L. Gen.Nafü.), Fu.MG (nachtjagdfähig), Jagdschloß, Mammut, Freya (+ An , + An & Kuh, + Kuh & Gemse, + Fahrstuhl), Würzburg (A-D, Riese, Riese + Gema Zusatz).
• Map size: 6x5 (WxH) A4-sheets. Map scale 1:2500000.
• Ref. 210V: "Jägermeßstellungen" (radar sites for fighter intercept guidance), Zeichgs-Nr. 44/17-2-A, GKdos, OKL. Gen.-Nafü, 1. Abt. III. Map is dated 20 June 1944. [file size: 61 MB; good-but-lower-resolution file is here, 25 MB]. Note: this map was rather poorly folded (6x5 layers) and not flat at all, which made it hard to stitch the indiviudal partial images back together. Source: BArch-MA/BAMA file nr. (Signatur) RL 2-V/9.
• Map covers area of northern Britain to northwestern Egypt. Map is marked with locations of Egon (Gerät, Gerät + AN, Gerät + A/K), Y-Stellung, Y-Gerät (operational, under construction, planned), Tagjadgenauigkeit, Nachtjagdgenauigkeit, and also boundaries of Zusatzzahlgebiete, Jagdtrapezbegrenzung.
• Map size: 6x5 (WxH) A4-sheets. Map scale 1:2500000.
• Ref. 210W: "Flugmeldeeinsatz- und Organisationsplanung", Zeichgs-Nr. 44/20-1-A, GKdos, OKL. Gen.-Nafü, 1. Abt. III. Map is dated 20 June 1944. [file size: 63 MB; good-but-lower-resolution file is here, 26 MB]. Source: BArch-MA/BAMA file nr. (Signatur) RL 2-V/9.
• Note: this map has the same background map as ref. 210V, but with some different mark-ups. Map covers area of northern Britain to northwestern Egypt. Map is marked with locations of Wassermann (L/M/S), Fu.MG (nachtjagdfähig), Mammut, Freya (+ An , + An & Gemse, + An & Kuh, + Kuh & Gemse, + Fahrstuhl), Würzburg (A-D, Riese, Riese + Gema Zusatz), and also boundaries of Zusatzzahlgebiete, Jagdtrapezbegrenzung.
• Map size: 6x5 (WxH) A4-sheets. Map scale 1:2500000.
• Ref. 210X: "Ln-Gerätestellungen im Landekopfraum" [Luftwaffe Signal Corps installations/sites]. Map is dated 24-June-1944. Source: BArch-MA/BAMA file nr. (Signatur) RL 2-V/235 (frmr. RL 2-V/5).
• Map is centered on Allied invasion beachheads in Normandie. Map is marked with location of LV, Fu.M.B., H-Peiler, Fu.M.G. Fu.Nav. (Y, Kn, E, Be), H.-Zug, Jägermeßstellungen, and s. & l. Funkfeuer sites. "Bernhard" stations Be-1 (Favières) and Be-4 (La Pernelle) are marked on this map.
• Map size: ca. 4x3½ (WxH) A4-sheets. Map scale 1:500000.
• Cover letter for the above map. Letter without subject, dated 24 June 1944, addressed to Chef Luftwaffe Führungsstab. Letter reference "Gen.Nafü. 1. Abt (I), Nr. 11 004/44 g. Kdos". Letter mentions scuttling/destruction of installations, transfer of forces from the Cotentin peninsula to Cherbourg, and numbers of German forces killed or taken prisoner.
• Ref. 210Y: "Ln.-Anlagen im Bereich der Ostfront" [Luftwaffe Signal Corps installations on the eastern front]. Map is dated 9 February 1945.  [file size: 103 MB; good-but-lower-resolution file is here, 21 MB]. Source: BArch-MA/BAMA file nr. (Signatur) RL-2-V-19.
• Map covers area from Denmark to Hungary. Map is marked with locations of Fu.MG (1. Ordnung, Eisenbahn, mot.), Funknav.-Anlagen (Egon, Zyklop, Sonne, Truhe), LVermittlung, Jägerleitstellungen, and Flugsicherungszentralen (Nachtjagd) sites. Map markings include "Bernhard" stations Be-0, Be-12, and Be-15. On the back of the map's legend panel, the map title is repeated, but changed by hand to "Ln.-Anlagen im Bereich der Front" and "Bereich Reichsgebiet 9.2.45".
• Map size: ca. 6x3½ (WxH) A4-sheets. Map scale is not marked.
• Ref. 210Z: "Flugsicherungseinheiten mit Nebenkarte Norwegen". Map is dated 1-Jan-1945, Gen.-Nafü 1/II.  [file size: 61 MB; good-but-lower-resolution file is here, 11 MB]. Source: BArch-MA/BAMA file nr. (Signatur) RL-2-V-19.
• Map covers area from Scandinavia to Romania. Map is marked with location of Flugsicherungshauptstellen, abgesetzte UKW Arbeitsplätze, Flugsicherungszentralen (Fluz), and Rgt. / Abt. / Komp. sites.
• Map size: ca. 4x3½ (WxH) A4-sheets. Map scale is 1:2000000.
• Ref. 210AA: "Flugsicherungszentralen Flugsicherungs-Hauptstellen", map covers area from The Netherlands to Hungary. Map is dated 1-January-1945, Gen.-Nafü 1/II. Source: BArch-MA/BAMA file nr. (Signatur) RL-2-V-19.
• Map is marked with location of Flugsicherungszentralen (Fluz; Kampf & Nachtjagd), Flugsicherungs-Haupstellen, abgesetzte UKW-Arbeitsplätze.
• Map size: ca. 4x2 (WxH) A4-sheets. Map scale 1:2000000.
• Ref. 210AB: "Drehkreuzachsen im Reichsgebiet". Map is dated 1-March-1945 with update on 22-March-1945, Gen.-Nafü.  [file size: 88 MB; good-but-lower-resolution file is here, 26 MB]. Source: BArch-MA/BAMA file nr. (Signatur) RL-2-V-19.
• Map covers area from Denmark to Hungary. Map is marked with location of "Drehkreuzachsen" lines (permanent phone lines, with wire-pairs twisted between masts), LV, LSZ, Jägermeßstellungen, Schaltstellen, TF-Verstärker.
• Map size: ca. 5x3½ (WxH) A4-sheets. Map scale 1:1000000.
• Ref. 210AC: "Gesamt-Drahtlage" [Complete com wire/cable map]. Map is dated 1-January-1945. [file size: 41 MB; good-but-lower-resolution file is here, 23 MB]. Source: BArch-MA/BAMA file nr. (Signatur) RL-2-V-19.
• Map covers area from Denmark to Hungary. Map is marked with location of Drehkreuzachsen, Heereslinien, Fernkabel, Breitbandkabel, U-Kabel, LF-Kabel, LV, Schaltstellen, LSZ, Verstärkerämter, Betriebsstellen.
• Map size: ca. 4x2 (WxH) A4-sheets. Map scale 1:2000000.
• Ref. 210AD: "Begriffsbestimmungen" [definitions/terminology], Anlage (appendix) to "Der Reichsmarschall d. Großdeutschen Reiches und Oberbefehlshaber der Luftwaffe Lw.Fü.St./Chef NVW Nr. 10 222/44 g.Kdos.(l/I) vom 28.2.44". Dated 28 february 1944. Page 6 missing from file. Source: BArch-MA/BAMA file nr. (Signatur) RL 2-V/5.
• Brief definition/clarifaction of the terms "Flugmeldedienst", "Flugwache" (Vollflugwache / Tagflugwache / Behelfsflugwache), "Fu.M.G.Stellung" (1. Ordung, 2. Ordnung, 3.Ordnung), Flugmeldezentrale (Stellungs-, Abschnitts-, Divisions-, Korps-, Flotten-), "Flugmelde-Bereiche" (Stellungs, - Abschnitts- (Flugmeldeabschnitt), Divisions-), "Einheiten des Flugmeldedienstes" (-Kompanie, -Abteilung-, -Regiment), "Flugmeldeauswertestelle eines Fliegerhorstes", "Florian-Netz", "Reportageverfahren", "Jägermeßdienst", "Jägermeßstellung", "Warnwache", "L.S.Warnkommando (L.S.Wako)", "L.S.Warnzentrale", "Eisenbahnflugwarnzentrale (Eflu-Wz.)", "Flugmeldposten der Flakartillerie".
• Ref. 210AE: "Taktische Zeichen für die Neuorganization des Flugmeldedienstes, Eintragung der Geräteausstattung der Fu.M.G.-Stellung, Darstellung des Ausbauzustandes, Taktische Zeichen für die Neuorganization des Jägerleitdienstes" [map & org-chart symbology for the Luftwaffe Aircraft Reporting Service, standard equipment configuratins for radar sites, map & org-chart symbology for the reorganized Fighter Guidance Service], 1944, 6 pp. Source: BArch-MA/BAMA file nr. (Signatur) RL 2-V/5.
• Ref. 212: "Flugzeug-Ausrüstungsgeräte - Teil 9, Mappe 637", RLM, Jan/Sept 1944; source: www.DeutscheLuftwaffe.de [file size 41 MB]
• Ref. 212A: pdf pp. 17, 18, 330-350, 388-392
• Ref. 212B: pdf p. 299 "Prüfuhr Ln 28901, PrU 28, 124-1416 A, T. Bäuerle u. Söhne, 1941/42"
• Ref. 221: "Dr. phil. Siegmund Loewe (1885-1962)", Herbert Börner, in "Funkgeschichte", Vol. 12 (1989), Nr. 67, pp. 9-13 [pdf]
• Ref. 228: Rotating loop- and reflector-beacons
• Ref. 228A: "Directional Wireless as an Aid to Navigation" [direction-finding, night effect, course-ranges, directional transmission, beam, VHF reflector-antenna, rotating loops, fixed-course loops], R.L. Smith-Rose, in "Nature", Volume 120, No. 3030, 26 November 1927, p. 774-776. Accessed 11 April 2020. [pdf]
• Ref. 228B: "Some experiments on the applications of the rotating-beacon transmitter to marine navigation", R.L. Smith-Rose, S.R. Chapman, in "Journal of the Institution of Electrical Engineers", Vol. 3 , Iss. 8, March 1928, pp. 256-269, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf]
• Ref. 228C: "Directional Wireless and Marine Navigation: the Rotating-Loop Beacon", R.L. Smith-Rose, in "Nature", Volume 121, 12 May 1928, p. 745.  [pdf]
• This is an update to ref. 228A.
• Ref. 228D: "Radio Direction-Finding by Transmission and Reception", R.L. Smith-Rose, in "Nature", Vol. 125, No. 3154, 12 April 1930, pp. 568-569. [pdf]
• Ref. 228E: "Some Observations on the Orfordness Rotating Beacon", R.L. Smith-Rose, in "Journal of the I.E.E.", Vol. 69, Iss. 412, April 1931, pp. 523-532, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf]
• Also published under the same title in "Proceedings of the Wireless Section of the Institution of Electrical Engineers", Vol. 6, Iss. 17/18 , June-September 1931, pp. 137-146. [Abstract].
• Ref. 228F: Reports of the UK Department of Scientific and Industrial Research, Radio Research Board (DSIR 11):
• Ref. 228F1: "An investigation of a Rotating Radio Beacon" [Gosport], R.L. Smith-Rose, S.R. Chapman, Research Report No. 6, 1928.
• Ref. 228F2: "The Orfordness Rotating Beacon and Marine Navigation" [principle of the beacon, bearing taking with stopwatch and automatic recorder, bearing accuracy], R.L. Smith-Rose, Special Report No. 10, 1931, 14 pp. [Abstract / report review].
• Ref. 228G: pp. 200-204 in "Rotating beacons", Section 4.12 of "Radio Aids to Civil Navigation", Reginald Frederick Hansford (ed.), Heywood & Co. Ltd. (publ.), 1960, 623 pp.
• Ref. 228H: British Air Ministry Notices/Pamphlets
• Ref. 228H1: "Orfordness Rotating Beacon : Instructions for taking bearings. (Provisional) : direction and position finding by means of directional wireless transmission", Pamplet No. 38, year unknown.
• Ref. 228H2: "Orfordness Rotating Radio Beacon", Notice No. 56 of 1929, in "Air Ministry Notices to Airmen, p. 1045 in "Flight", Vol. XXI, no. 38, 20 September 1929, 56 pp. Source: archive.org. Accessed 3 May 2020.
• Ref. 228H3: "Orfordness rotating radio beacon", General Notice No. 19 of 1930.
• Ref. 228H4: "Farnborough Rotating Wireless Beacon", General Notice No. 31 of 1930, in "Air Ministry Notices to Aircraft Owners and Ground Engineers", p. 1388 in "Flight", Vol. XXII, No. 48, 28 November 1930. Source: archive.org. Accessed 3 May 2020.
• Ref. 228H5: "Farnborough rotating wireless beacon" - General Notice No. 33 of 1930.
• Ref. 228H6: "Farnborough and Orfordness rotating wireless beacons", Notice No. 43 of 1931 Series A, p. 823 in "Flight", Vol. XXIII, No. 33, 14 August 1931, 26 pp. Source: archive.org. Accessed 4 May 2020.
• Ref. 228H7: "Orfordness rotating radio beacon", Notice No. 21 of 1932 Series A, p. 499 in "Flight", Vol. XXIV, No. 23, 3 June 1932, 22 pp. Source: archive.org. Accessed 3 May 2020.
• Ref. 228H8: "Orfordness rotating radio beacon", Notice No. 58 of 1932 Series A.
• Ref. 228H9: "Orfordness and Tangmere rotating radio beacons", Notice No. 30 of 1933 Series A.
• Ref. 228H10: "Orfordness rotating radio beacon", Notice No. 63 of 1933 Series A.
• Ref. 228H11: "Orfordness radiobeacon", Notice No. 32 of 1938. Excerpt.
• Ref. 228J: "Direction-Finding System (Beacon)", UK Parliament, Commons Chamber, Record of Oral Answers To Questions, Vol. 222, nr. 29, 21 November 1928. Source: hansard.parliament. Accessed 3 May 2020.
• Ref. 228K: "First of the Beams", 9 pp. in "Inter-War Years", Chapter 5 in "Most Secret: The Hidden History of Orford Ness", Paddy Heazell, The History Press (publ.), 2011, 256 pp. Accessed 4 May 2020. [pdf]
• Ref. 228L: "Note on a special dial for time-pieces to be used with rotating wireless or other beacons", R.L. Smith-Rose, in "Journal of Scientific Instruments", Vol. 5, No. 3, 1 March 1928, pp. 93-96 [file size: 49 MB], . Accessed 4 May 2020.
• Ref. 228M: "An automatic recorder of signals from a rotating beacon transmitter", R.L. Smith-Rose, H.A. Thomas, in "Journal of Scientific Instruments", Vol. 8, No. 3, 1 March 1931, pp. 81-88, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]   Also published in "The Nautical Magazine", Vol. 127, January 1932 [2-page extract].
• Ref. 228N: pp. 35, 36, 79, 87, 154 in "1939 Radio Aids to Navigation - Including Details of Direction-finder Stations, Radiobeacons, Navigational Warnings, Time Signals, Etc.", United States Hydrographic Office (Navy Dept., Bureau of Navigation), publication H.O. No. 205, 1939, 315 pp.
• Ref. 228P: "The invention of synchronous rotations by means of Paul la Cour's Phonic Wheel as used in Telegraphy", P. Chr. Dresing, in "The Telegraphic Journal and Electrical Review", Vol. XX, No. 476, 7 January 1887, pp. 31, 32.
• Ref. 228Q: "Orford Ness: the Black Beacon and associated power house", National Heritage List for England (NHLE). Accessed 8 May 2020. [pdf]
• Ref. 228R: pp. 454-455 in "Wireless - A treatise on the theory and practice of high-frequency electric signalling" [Farnborough rotating beacon], L.B. Turner, Cambridge University Press (publ.), 1931, 531 pp. Source: archive.org [file size: 32 MB]. Accessed 10 May 2020.
• Ref. 228S: articles in "Journal of the Institution of Electrical Engineers", Vol. 66, Iss. 375, March 1928.
• Ref. 228S1: "Rotating-loop radio transmitters, and their application to direction-finding and navigation", T.H. Gill, N.F.S. Hecht, in "Journal of the Institution of Electrical Engineers", Vol. 66, Iss. 375, March 1928, pp. 241-255, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]. Also reprinted in "Proceedings of the Wireless Section of the Institution of Electrical Engineers", Vol. 3, Iss. 8, June 1928, pp. 69-83.
• Ref. 228S2: "Some experiments on the applications of the rotating-beacon transmitter to marine navigation", R.L. Smith-Rose, S.R. Chapman, in "Proceedings of the Wireless Section of the Institution of Electrical Engineers", Vol. 3, Iss. 8, June 1928, pp. 256 -269, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1].
• Ref. 228S3: "A theoretical discussion of various possible aerial arrangements for rotating-beacon transmitters", R.L. Smith-Rose, in "Journal of the Institution of Electrical Engineers", Vol. 66, Iss. 375, March 1928, pp. 270-279, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1].
• Ref. 228S4: "Discussion on the papers “Rotating-loop radio transmitters, and their application to direction-finding and navigation”, by Messrs. Gill and Hecht, “Some experiments on the applications of the rotating-beacon transmitter to marine navigation”, by Messrs. Smith-Rose and Chapman, and “A theoretical discussion of various possible aerial arrangements for rotating-beacon transmitters”, by Dr. Smith-Rose, respectively, before the Wireless Section, 4th January, 1928", in "Journal of the Institution of Electrical Engineers", Vol. 66, Iss. 375, March 1928, p. 274-278. Source: en.booksc.org, accessed April 2021. [pdf, See note 1].
• Ref. 228S5: "The authors' replies to the discussion on “Rotating-loop radio transmitters, and their application to direction-finding and navigation”, “Some experiments on the applications of the rotating-beacon transmitter to marine navigation” and “A theoretical discussion of various possible aerial arrangements for rotating-beacon transmitters”, T.H. Gill, N.F.S. Hecht, R.L. Smith-Rose, S.R. Chapman, in "Journal of the Institution of Electrical Engineers", Vol. 66, Iss. 375, March 1928, pp. 278-279. Source: en.booksc.org, accessed April 2021. [pdf, See note 1].
• Ref. 228T: documentation about the Orfordness beacon, available at The National Archives, Kew/England
• Ref. 228T1: "COMMUNICATIONS. Wireless: Orfordness; erection of an experimental wireless rotating beacon", archive file Catalog reference T 161/576/1, file covers period 24 May 1928 - 4 May 1933.
• Ref. 228T2: "Signals (Code 133): Rotating wireless beacon - Orfordness. Key number(s): 5688, 4496....", archive file Catalog reference MT 9/1951, file covers period 1928 - 1930, file contains 14 items.
• Ref. 228U: p. 345, 346 in "New Aids to Navigation and Pilotage", K.E.L. Creighton, in "Royal United Services Institution Journal", Vol. 77, Iss. 506, May 1932, pp. 341-358. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 228V: articles about Marconi's (and others') parabolic reflector antenna beacons, the Marconi company, and Guglielmo Marconi himself.
• Ref. 228V1: "The "Radio Lighthouse" - An Amazing New Use for Marconi Beams", p. 77 in "Popular Science Monthly", Vol. 105, No. 6, December 1924. Accessed 10 May 2020.
• Ref. 228V2: "Short-wave Directional Wireless Telegraph" [reflector antennas, Inchkeith beacon], C.S. Franklin, in "Nature", Vol. 110, No. 2754, 12 August 1922. Accessed 10 May 2020. [pdf]
• Ref. 228V3: "The Marconi wireless beam reflector on Inchkeith", N. Wells, in "Engineering", Vol. 119, 13 March 1925, p. 309-311.
• Ref. 228V4: pp. 10-13 in "Short wave wireless communication", Alan Wilfrid Ladner, Charles Robert Stoner, John Wiley & Sons, Inc. (publ.), 1933, 348 pp. Source: hathitrust.org, retrieved 20 October 2020.
• Ref. 228V5: pp. 442-444, 455 in "Wireless: A Treatise On The Theory And Practice Of High-Frequency Electric Signalling", L. B. Turner, Cambridge University Press, 1931, 578 pp. Source: archive.org, retrieved 20 October 2020.
• Ref. 228V6: "Short-wave directional wireless telegraphy", C.S. Franklin, in "The Wireless World and Radio Review",Vol. X, No. 8, 20 May 1922, p. 219-225. Source: worldradiohistory.com, retrieved 13 January 2021.
• Ref. 228V7: "Directional short - wave wireless telephony", §6 in "Electrons, electric waves and wireless telephony - XIX", J.A. Fleming, in "The Wireless World and Radio Review", No. 182 (Vol. XI, No. 19), 10 February 1923, p. 626-629. Source: archive.org, retrieved 13 January 2021.
• Ref. 228V8: "Directional wireless as an aid to navigation", in "The Wireless World and Radio Review", No. 189 (Vol. XI, No. 26), 31 March 1923, pp. 859-860. Source: archive.org, retrieved 13J anuary 2021.
• Ref. 228V9: "How Marconi has conquered fogs with a lightless lighthouse - revealing secrets of the wireless wizard's new "one way" radio which may supplant light buoys and other signal devices guiding ships at sea", in "The Shreveport Times" (Shreveport/USA), Vol. L, No. 96, 3 September 1922, p. 35.
• Ref. 228V10: "The wireless beam" [Marconi, reflector beam at Inchkeith, shipping], in "The Manchester Guardian", 15 May 1924, p. 16
• Ref. 228V11: "Safeguarding sea with beam transmitters - Radio beacon guides ships despite fog: Marconi invention safeguards vessels" [Marconi revolving reflector at South Foreland, narrow beam, wavelength 6 m = 50 MHz, 16 compass points marked with Morse coder letter, shipping], in "The Pittsburgh Post", Vol. 83, No. 303, 18 November 1925, p. 13.
• Ref. 228V12: "Reflected wave employed as lighthouse off Scotland" [Marconi, Inchkeith, 4.28 m wavelength = 70 MHz, revolving reflector antenna, 8m aperture, 1/2 rpm, spark transmitter, distinctive signal at 1/2 or 1/4 compass points, Morse letter each 2 compass points, 2.8° bearing determination, stop watch method], in "Calgary Herald" (Alberta/Canada), Vol. 38, No. 4539, 26 August 1922, p. 28.
• Ref. 228V13: "Short wave directive radio transmission" [experiments at ca. 30 MHz (10 m wavelength), 50 W tube transmitter, vertical cage dipole with parabolic reflector], Francis W. Dunmore, Francis H. Engel, in "Radio News", Vol. 5, No. 2, August 1923, pp. 128-130, 182, 184. Source: worldradiohistory.com, retrieved 4 April 2021. Also published as "Short-wace
• Ref. 228V14: "Radio Telegraphy" [Inchkeith beacon], Senatore Guglielmo Marconi, in "Proc. of the IRE", Vol. 10, Nr. 4, August 1922, pp. 215-238.  Source: worldradiohistory.com, retrieved 19 April 2021. Reprint: in "Proc. of the IRE", Vol. 50, Nr. 8, August 1962, pp. 1748-1757. Source: en.booksc.org, accessed April 2021. [pdf (better quality than the scan of the 1922 article), See note 1]
• Ref. 228V15: "A history of the Marconi Company", W.J. Baker, St. Martin's Press (publ.), 1971, 433 pp. Source: nvhrbiblio.nl, retrieved 3 May 2021.
• Ref. 228V16: "The Heinrich Hertz wireless experiments at Karlsruhe in the view of modern communication", D.J. Cichon, W. Wiesbeck, in "Proc. IEE International Conference on 100 Years of Radio", London/UK, September 1995, 6 pp. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 228W: "East coast beacon for airmen" [Orfordness rotating radio beacon operational], in "The Manchester Guardian", 10 September 1929, p. 6.
• Ref. 228X: "Wireless apparatus", R. L. Smith-Rose, in "Journal of Scientific Instruments", Vol. 8, nr. 2, February 1931, pp. 66-69. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 228Y: "A Method of Exciting the Aerial System of a Rotating Radio Beacon", H.A. Thomas, in "Institution of Electrical Engineers - Proceedings of the Wireless Section of the Institution", Vol. 10, Iss. 30, September 1935, 256-261. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 228Z: "Radio Research", S.K. Lewer, in "Science Progress in the Twentieth Century", Vol. 25, No. 98, October 1930, pp. 315-319.
• Ref. 229: civil equi-signal beam systems (Scheller, Fixed-course & Four-Course ranges, E/T & A/N beacons, Visual Ranges, Visual Aural Ranges)
• Ref. 229A: articles in German and Dutch language
• Ref. 229A1: "Über die Wirkung von Schellers drahtlosen Kursweiser auf das Flugzeug" ["About the impact of Scheller's wireless direction pointer on aircraft", Eberhard Buchwald, in "Zeitschrift für drahtlose Telegraphie und Telephonie sowie des Gesamtbereichs der elektromagnetischen Schwingungen", Vol. 15, Nr. 2, February 1920, pp. 114-122. Source: hathitrust.org, retrieved April 2021.
• Ref. 229A2: "Neue Versuche über funkentelegraphische Richtsender" ["New trials with directional spark transmitter stations"; A/N system], Franz Kiebitz, in "Zeitschrift für drahtlose Telegraphie und Telephonie sowie des Gesamtbereichs der elektromagnetischen Schwingungen", Vol. 15, Nr. 4, April 1920, pp. 299-310.
• Ref. 229A3: "Zur Geschichte der Richtwirkungs- und Peilversuche auf den Flugplätzen Döberitz und Lärz" ["History of radio directivity- and direction-finding tests at Döberitz and Lärze airfields"], Richard Baldus, Eberhard Buchwald, Rudolf Hase, in "Jahrbuch - Zeitschrift für drahtlose Telegraphie und Telephonie", Vol. 15, Nr. 2, February 1920, pp. 99-100. Source: hathitrust.org, retrieved April 2021.
• Ref. 229A4: "Über Richtempfangsversuche im Flugzeug" ["About directional reception in airplanes"], Eberhard Buchwald, in "Jahrbuch - Zeitschrift für drahtlose Telegraphie und Telephonie", Vol. 15, Nr. 2, February 1920, pp. 101-113. Source: hathitrust.org, retrieved April 2021
• Ref. 229A5: "Das Kaiserliche Telegraphen-Versuchsamt" ["The Imperial Telegraphy Test Institute"], in "Telefunken Zeitung", Vol. 3, No. 1, January 1914, pp. 7-9. Source: radiomuseum.org, retrieved 11 April 2021.
• Ref. 229A6: "Neuere Arbeiten auf dem Funkbaken-Gebiete" ["Recent work in the field of radio beacons"; Lorenz, E/T keying, magnetic-bias keying, VHF beacon], Ernst Kramar, "Hochfrequenztechnik und Elektroakustik", Vol./Nr. 40, September 1932, pp. 88-92. [Abstract].
• Ref. 229A7: "Lorenz-ultra-korte golf-landingsbaken voor vliegtuigen" ["Lorenz VHF landing beacon for aircraft"], H. Veenstra (Lorenz; based on E. Kramar), in "Radio-Nieuws", Vol. 18, Nr. 3, 15 May 1935, pp. 49-61. Source: nvhrbiblio.nl, retrieved 24 May 2022.
• Ref. 229A8: "De Nederlandsche radiobakens" ["The Dutch radio beacons"; incl. B.R.A. 101], pp. 59-66 in "Radio en Luchtvaart" ["Radio and aviation"], S. van der Molen, No. 5 of "Meulenhoff's Luchtvaartserie", J.M. Meulenhoff (publ.), 1936, 107 pp. Source: us.archive.org, retrieved 22 May 2022.
• Ref. 229B: "Radio range flying", C.H. McIntosh, J.L. Adams, F.C. Ringer, Ringer Press (publ.), 1941, 62 pp. Source: hathitrust.org, retrieved 1 April 2021.
• Ref. 229C: articles in "Electrical Communication - Technical Journal of the International Telephone and Telegraph Corporation and Associate Companies". Source: worldradiohistory.com. Accessed January-August 2020.
• Ref. 229C1:"Otto Scheller and the Invention and Applications of the Radio-Range Principle" [incl. ITT Landing System, SCS-51 (mobile)], R.I. Colin, in "ITT Electrical Communication", Vol. 40, Nr. 3, 1965, pp. 359-368, retrieved 23 January 2020. [Summary]. Reprinted as "Otto Scheller: The Radio Range Principle", R.I. Colin, in "IEEE Trans. on Aerospace and Electronic Systems", Vol. AES-2, No. 4, July 1966, pp. 481-487 [pdf].
• Ref. 229C2: "Federal Telephone and Radio Corporation - A historical review: 1909-1946" [incl. spark transmitter, arc transmitter, Duddell, Poulsen, Federal Telegraph Company, Mackay System, ITT], F.J. Mann, in "ITT Electrical Communication", Vol. 23, No. 4, December 1946, pp. 377-406.
• Ref. 229C3: "An Ultra-High Frequency Radio Range with Sector Identification and Simultaneous Voice", Andrew Alford, Armig G. Kandoian, Frank J. Lundburg, Chester B. Watts, in "Electrical Communication" Journal of the Int'l Telephone & Telegraph Corp. and Associated companies", Vol. 23, No. 2, 1946, pp. 179-189.
• Ref. 229D: Papers published in the "Bureau of Standards Journal of Research". Source: US National Institute of Standards and Technology (NIST). Accessed March-April 2020. Also articles about activities of the Bureau of Stds.
• Ref. 229D1: "A 12-Course Radio Range for Guiding Aircraft with Tuned Reed Visual Indicator", H. Diamond, F.G. Kear, Research Paper 154 (RP154), in "Journal of Research", Vol. 4, Issue 3, March 1930, pp. 351-369. [pdf] [Abstract]
• Ref. 229D2: "Applying the Radio Range to the Airways", F.G. Kear, W.E. Jackson, Research Paper 155 (RP155), in "Journal of Research", Vol. 4, Issue 3, March 1930, pp. 371-381. [pdf] [Abstract]. NOTE: this article was also published in the Proc. of the IRE, see ref. 229L8.
• Ref. 229D3: "Development of the Visual Type Airway Radio-Beacon System", J.H. Dellinger, H. Diamond, F.W. Dunmore, Research Paper RP159, in "Journal of Research", Vol. 4, Issue 3, March 1930, pp. 425-459.  [pdf]   [Abstract, Summary]
• Ref. 229D4: "The cause and elimination of night effects in radio range-beacon reception", H. Diamond, Research Paper 513 (RP513), in "Journal of Research", Vol. 10, Issue 1, January 1933, pp. 7-34. [pdf]
• Ref. 229D5: "A radiobeacon and receiving system for blind landing of aircraft", H. Diamond, F.W. Dunmore, Research Paper 238 (RP238), in "Journal of Research", Vol. 5, Issue 4, October 1930, pp. 897-931. [pdf]
• Ref. 229D6: "Unidirectional radiobeacon for aircraft", E.Z. Stowell, Research Paper 35 (RP35), in "Journal of Research", Vol. 1, Issue 6, December 1928, pp. 1011-1022. [pdf]   [Abstract]
• Ref. 229D7: "Applying the visual double-modulation type radio range to the airways", Research Paper 148 (RP148), H. Diamond, in "Journal of Research", Vol. 4, Issue 3, March 1930, pp. 265-289. [pdf]   [Abstract]
• Ref. 229D8: "A course-shift indicator for the double-modulation type radiobeacon", H. Diamond, F.W. Dunmore, Research Paper 77 (RP77), in "Journal of Research", Vol. 3, Issue 1, 1 July 1929 (paper dates from 20 February 1929), 10 pp. [pdf]
• Ref. 229D9: "A tuned-reed course indicator for the 4 and 12 course aircraft radio range", F.W. Dunmore, Research Paper RP160, in "Journal of Research", Vol. 4, Issue 4, April 1930, pp. 461-474. [pdf]   [Abstract]
• Ref. 229D10: "Design of tuned reed course indicators for aircraft radiobeacon", F.W. Dunmore, Research Paper 28 (RP28), in "Journal of Research", Vol. 1, Issue 5, November 1928, pp. 751-769. [pdf, file size: 26 MB]
• Ref. 229D11: "A method of providing course and quadrant identification with the radio range-beacon system" [Adding a vertical antenna to the cross-loops], F.W. Dunmore, Research Paper 593 (RP593), in "Journal of Research", Vol. 11, Issue 3, September 1933, pp. 309-325. [pdf] [Abstract]
• Ref. 229D12: "The Radio Work of the Dept. of Commerce", J.H. Dellinger, in "QST", June 1921, pp. 18-21. Accessed 14 April 2020. [pdf]
• Ref. 229D13: "A Century of WWV", Glenn K. Nelson, in "Journal of Research of the National Institute of Standards and Technology", Vol. 124, Article 124025, 2019. Accessed 14 April 2020. [pdf]
• Ref. 229D14: "Radio publications of the Bureau of Standards", NBS DoC, Letter Circular LC 40, 25 November 1922, 22 pp. Accessed 14 April 2020. [pdf]
• Ref. 229D15: "Radio - The aviator's guiding hand", pp. 147-170 in "Antennas, instruments, and systems in development" Chapter VI in "Achievement in Radio - Seventy Years of Radio Science, Technology, Standards, and Measurements at the National Bureau of Standards" [file size: 72 MB; history of the NBS radio section], Wilbert F. Snyder, Charles L. Bragaw, National Bureau of Standards, NIST Special Publication 55 (SP555), October 1986, 884 pp. Accessed 14 April 2020. [pdf, file size: 72 MB]
• Ref. 229D16: "Automatic volume control for aircraft radio receivers", W.S. Hinman, Research Paper 330 (RP330), in "Journal of Research", Vol. 7, Issue 1, July 1931, pp. 37-46. Accessed 15 July 2020. [pdf]
• Ref. 229D17: "A Course Indicator of Pointer Type for the Visual Radio Range-Beacon System", F.W. Dunmore, Research Paper 336 (RP 336), in "Journal of Research", Vol. 7, Issue 1, July 1931, pp. 147-170. Accessed 5 June 2020. [pdf] [Abstract]
• Ref. 229D18: "Theory of design and calibration of vibrating-reed indicators for Radio Range beacons", G.L. Davies, in "Journal of Research", Vol. 7, Issue 1, July 1931, pp. 195-213. Accessed 10 June 2020. [pdf] [Abstract] NOTE: this article was also published in the Proc. of the IRE, see ref. 229L13.
• Ref. 229D19: "A simultaneous radiotelephone and Visual Range beacon for the airways", F.G. Kear, G.H. Wintermute, Research Paper 341 (RP341) in "Journal of Research", Vol. 7, Issue 2, August 1931, pp. 261-287. Accessed 10 June 2020. [pdf] [Abstract] NOTE: this article was also published in the Proc. of the IRE, see ref. 229L7.
• Ref. 229D20: "Phase Synchronization in Directive Antenna Arrays with Particular Application to the Radio Range Beacon", F.G. Kear, Research Paper 581 (RP581), in "Journal of Research", Vol. 11, No. 1, July 1933, pp. 123-140. [pdf] [Abstract]
• Ref. 229D21: "A course-shift indicator for the double-modulation type radiobeacon", H. Diamond, F.W. Dunmore, in "Journal of Research", Vol. 3, Issue 1, July 1929, p. 1. [pdf]
• Ref. 229D22: "Graphical determination of polar patterns of directional antenna systems", G.L. Davies, W.H. Orton, Research Paper 435 (RP435), in "Journal of Research", Vol. 8, Issue 5, May 1932, pp. 555-569. [pdf]
• Ref. 229D23: "Performance tests of radio system of landing aids", H. Diamond, Research Paper 602 (RP602), in "Journal of Research", Vol. 11, Issue 4, October 1933, pp. 463-490. [pdf] [Abstract]
• Ref. 229D24: "A radio direction finder for use on aircraft", Wilbur S. Hinman, Research Paper 621 (RP621), in "Journal of Research", Vol. 11, Issue 6, December 1933, pp. 733-741. [pdf] [Abstract]
• Ref. 229D25: "Experiments with underground ultra-high-frequency antenna for airplane landing beam", Harry Diamond, Francis W. Dunmore, Research Paper 1006 (RP1006), in "Journal of Research", Vol. 19, Nr.1, July 1937, 19 pp. [pdf] [Abstract]. NOTE: this article was also published in the Proc. of the IRE, see ref. 229L17.
• Ref. 229D26: "Consolidated Instrument Company" & "The Radio-beacon Tuned Reed Indicator", pp. 44 & 74 in "US Air Services - Feature Aeronautical Magazine, Commercial and Military", November 1929. [contract to manufacture the U.S. Bureau of Standards Visual Radio beacon Vibrating Reed Indicator awarded to Julien P. Friez & Sons, Inc., Baltimore/MD, subsidiary of Consolidated Instrument Co. of America, Inc.].
• Ref. 229D27: "The comparative accuracy of various existing and proposed radio navigation systems" [Radio Range, azimuthal-type, hyperbolic-type, composite range/azimuth type], William Q. Chrichlow, National Bureau of Standards, Central Radio Propagation Laboratory [ = Department of Commerce, Boulder/CO, Laboratories Building 1], Report No. CRPL-4-1, 30 December 1946, 44 pp. Source: nist.gov, retrieved 20 October 2020.
• Ref. 229D28: "Receiving sets for aircraft beacon and telephony", Haraden Pratt, Harry Diamond, in "J. of Research", Vol. 1, Issue 4, October 1928, pp. 543-563, Research Paper 19 (RP19), 19 June 1928, 23 pp. Source: nist.gov, retrieved 23 February 2021.
• Ref. 229D29: "Characteristics of airplane antennas for radio range-beacon reception" [vertical, T-, L-, V-antennas] H. Diamond, G.L. Davies, in "J. of Research", Vol. 6, Issue 5, May 1931, pp. 901-916, Research Paper 313 (RP313), 24 January 1931, 16 pp. Source: nist.gov, retrieved 23 February 2021.
• Ref. 229D30: "Theory of design and calibration of vibrating reed indicators for radio range beacons", G.L. Davies, in "J. of Research", Vol. 7, Issue 1, July 1931, pp. 195-213, Research Paper 338 (RP338), 25 March 1931, 19 pp. Source: nist.gov, retrieved 23 February 2021.
• Ref. 229E: Papers published in "Scientific Papers of the Bureau of Standards". Source: US National Institute of Standards and Technology (NIST). Accessed April 2020.
• Ref. 229E1: "A Directive Type of Radio Beacon and its Application to Navigation" [test/eval of multi-turn crossed-loop antennas, A/N equi-beam, effect of aircraft trailing-wire receive antenna], F.H. Engel, F.W. Dunmore, in "Scientific Papers of the Bureau of Standards", Vol. 19, No. 480 (S480), 8 September 1923, pp. 281-295.  [pdf] [Summary]
• Ref. 229E2: "Directive radio transmission on a wave length of 10 meters" [successful experiments of making the radiation pattern of a vertical dipole directional, with various configs of a reflector screen made of tuned & un-tuned vertical wires; shortwave, instead of then-standard long & medium wave], Francis W. Dunmore, Francis H. Engel, in "Scientific Papers of the Bureau of Standards", Vol. 19, Scientific Paper No. 469 (S469), 9 January 1923, pp. 1-16. [pdf] Extract was publised as "Short-wave directive transmission - constructional details of the transmitting and receiving equipment", in "The Wireless World and Radio Review", No 202 (Vol. XII, Nr. 13), 30 June 1923, pp. 419- 422. Source: worldradiohistory.com, retrieved 21 April 2021.
• Ref. 229E3: "Principles of radio transmission and reception with antenna and coil aerials", J.H. Dellinger, Scientific Paper No. 354 (S354), Scientific Papers of the Bureau of Standards, Vol. 15, June 1919, pp. 435-495. [pdf]
• Ref. 229E4: "The radio direction finder and its application to navigation", Frederick A. Kolster, Francis W. Dunmore, Scientific Paper 428 (S428), July 1921), Scientific Papers of the Bureau of Standards, Vol. 17, January 1922, pp. 529-566. [pdf]
• Ref. 229E5: "The field radiated from two horizontal coils", G. Breit, Scientific Paper No. 431 (S431), Scientific Papers of the Bureau of Standards, Vol. 17, Issue 3, 1922, pp. 589-606. [pdf]
• Ref. 229F: web page "The Evolution of Airway Lights and Electronic Navigation Aids", Roger Mola, U.S. Centennial of Flight Commission, 2003. [pdf]
• Ref. 229G: "The Equi-Signal Zone Radio Beacon and Air Navigation", R.L. Smith-Rose, in "Nature", Vol. 126, No. 3168, 19 July 1930, pp. 98-100. Accessed 1 March 2020. [pdf]
• Ref. 229H: Yagi-Uda directional multi-element focussed beam antenna
• Ref. 229H1: "Projector of the Sharpest Beam of Electric Waves", Hidetsugu Yagi, Shintaro Uda, in "Proceedings of the Imperial Academy" (Japan), Vol. 2, Iss. 2, 1926, pp. 49-52. [pdf]
• Ref. 229H2: p. 214 in "Highlighting the History of Japanese Radio Astronomy: 1: An Introduction", M. Ishiguro, W. Orchiston, K. Akabane, N. Kaifu, M. Hayashi, T. Nakamura, R.Stewart, H.Yokoo, in "Journal of Astronomical History and Heritage", Vol. 15, No. 3, November-December 2012, pp. 213-231. Source: narit.or.th, retrieved 8 April 2021
• Ref. 229H3: "Notes on the history of the Yagi-Uda antenna", Yasuto Mishiake, in "IEEE Antennas and Propagation Magazine", Vol. 56, No. 1, february 2014, pp. 256-257. Source: sm.rim.or.jp, retrieved 5 April 2021.
• Ref. 229J: "Lighting the Airways" and "The Emergence of Radio", in Chapter II "The Republican Era, 1926-1932", in "Bonfires to beacons: Federal civil aviation policy under the Air Commerce Act, 1926-1938" [file size: 29 MB], Nick A. Komons, U.S. Department of Transportation / Federal Aviation Administration (publ.), 1978, 472 pp. Source: hathitrust.org, accessed 21 May 2020. 
• Ref. 229K: "Radio range and blind flying: almost a decade of monumental aeronautical growth (1929-1936)", Chapter 4 (pp. 105-144) in "Flying the beam: navigating the early US airmail airways, 1917-1941", Henry R. Lehrer, Purdue University Press (publ.), ISBN 9781557536853, 2014, 234 pp.
• Some pages from Chapter 4.
• Ref. 229L: articles in Proceedings of the Institute of Radio Engineers. Source: worldradiohistory.com, retrieved June 2014 - June 2020.
• Ref. 229L1: "Apparatus used on British and European Airways", Edward H. Furnival, in "Proc. of the I.R.E", Vol. 17, Nr. 12, December 1929, pp. 2123-2136.
• Ref. 229L2: "The civil airways and their radio facilities", H.J. Walls, in "Proc. of the I.R.E.", Vol. 17, Nr. 12, December 1929, pp. 2141-2157.
• Ref. 229L3: "Applying the visual double-modulation type Radio Range to the airways", H. Diamond, in "Proc. of the I.R.E", Vol. 17, Nr. 12, December 1929, pp. 2158-2184. [Abstract]
• Ref. 229L4: "Radio in aeronautics - Its technical status and the organization for its application in Germany", F. Eisner, H. Fassbender, in "Proc. of the I.R.E.", Vol. 17, Nr. 12, December 1929, pp. 2185-2229.
• Ref. 229L5: "Applying the Radio Range to the airways", F.G. Kear, W.E. Jackson, in "Proc. of the I.R.E.", Vol. 17, Nr. 12, December 1929, pp. 2268-2282.   [Abstract]. NOTE: this article was also published in the Bureau of Standards Journal of Research, see ref. 229D2.
• Ref. 229L6: "Radio beacons for transpacific flights", Clayton C. Shangraw, in "Proc. of the I.R.E.", Vol. 16, Nr. 9, September 1928, pp. 1203-1235. [Abstract].
• Ref. 229L7: "A simultaneous radiotelephone and Visual Range beacon for the airways", F.G. Kear, G.H. Wintermute, in "Proc. of the I.R.E.", Vol. 20, Nr. 3, March 1932, pp. 478-515. NOTE: this article was also published in the Bureau of Standards Journal of Research, see ref. 229D18. [Abstract].
• Ref. 229L8: "Development of radio aids to air navigation", J.H. Dellinger, Haraden Pratt, in "Proc. of the I.R.E.", Vol. 16, No. 7, July 1928, pp. 890-920. [Abstract].
• Ref. 229L9: "Apparent Night Variations with Crossed-coil Radio Beacons", Haraden Pratt, in "Proc. of the I.R.E.", Vol. 16, Nr. 5, May 1928, p. 652-657. [Abstract].
• Ref. 229L10: "Simultaneous Radio Range and Telephone Transmission", W.E. Jackson, D.M. Stuart, in "Proc. of the I.R.E.", Vol. 25, Nr. 3, March 1937, pp. 314-326.  [Abstract].
• Ref. 229L11: "Radio Guidance" [two rotating radio beacons (simultaneously on the same frequency), triangulation on a display (physical map in aircraft instrument + projecting 2 intersecting light beams)], J. Edward Miller, in "Proc. of the I.R.E.", Vol. 20, Nr. 11, November 1932, pp. 1752-1762. [Abstract].
• Ref. 229L12: "Loop antennas for aircraft" [D/F], George F. Levy, in "Proc. of the I.R.E.", Vol. 31, Nr. 2, February 1943, pp. 56-66. [Abstract].
• Ref. 229L13: "Theory of design and calibration of vibrating-reed indicators for Radio Range beacons", G.L. Davies,  in "Proc. of the I.R.E.", Vol. 20, Nr. 1, January 1932, pp. 161-181. [Abstract]. NOTE: this article was also published in the Bureau of Standards Journal of Research, see ref. 229D17.
• Ref. 229L14: "The Development of a Visual Type of Radio Range Transmitter Having a Universal Application to the Airways" [very comprehensive!!! 4-course, 12-course visual range, transmitters, frequency tripler, loops, goniometer], W.E. Jackson, S.L. Bailey, in "Proc. of the IRE", Vol. 18, Nr. 12, December 1930, pp. 2059-2101. [Abstract]
• Ref. 229L15: "A Radio Range beacon free from night effects", Howard Allan Chinn, in "Proc. of the I.R.E.", Vol. 21, Nr. 6, June 1933, pp. 802-807.
• Ref. 229L16: "On the solution of the problem of Night Effects with the Radio Range beacon system", H. Diamond, in "Proc. of the I.R.E.", Vol. 21, Nr. 6, June 1933, pp. 808-832. [Abstract]
• Ref. 229L17: "Rectangular short-wave frame aerials for reception and transmission", L.S. Palmer, D. Taylor, in "Proc. of the I.R.E.", Vol. 22, Nr. 1, January 1934, pp. 93-114
• Ref. 229L18: "Experiments with underground ultra-high-frequency antenna for airplane landing beam", Harry Diamond, Francis W. Dunmore, in "Proc. of the I.R.E.", Vol. 25, Nr. 12, December 1937, pp. 1542-1560. [Abstract] Note: this article was also published in the Bureau of Standards Journal of Research, see ref. 229D25.
• Ref. 229L19: "The status of instrument landing systems" [overview BoS activities, test at College Park/MD & Newark, Lorenz 1933 40 MHz and kick-meter, US Army 1932/33 at Wright Field, Lorenz/ITT tests at Indianapolis issues, Bendix/UAL tests 1936 with yagi antennas], William Elvin Jackson, in "Proc. of the I.R.E.", Vol. 26, Nr. 6, June 1938, pp. 681-699. [Abstract]. Note: same article was also published in 1937 as CAA Technical Development Report No. 1 (ref. 229R20).
• Ref. 229L20: "The Ultra-Short-Wave Guide-Ray Beacon and Its Application", E. Kramar, W. Hahnemann, in "Proc. of the I.R.E.", Vol. 26, No.1, January 1938, pp. 17-44.
• Ref. 229L21: "Ultra-Short-Wave Propagation", Paul von Handel, Wolfgang Pfister, in "Proc. of the IRE", Vol. 25, Nr. 3, March 1937, pp. 346-363.
• Ref. 229L22: "Field intensity characteristics of double modulation type of directive radio beacon", Haraden Pratt, in "Proc. IRE", vol. 17, Nr. 5, May 1929, pp. 873-878. Source: worldradiohistory.com, retrieved 23 February 20121.
• Ref. 229M: "Adcock Antennas" [4-Course A/N systems], section 1.13.3 in "Radio Antenna Engineering", Edmund A. Laport, McGraw-Hill Book Co. (publ.), 1952, 574 pp.
• Ref. 229N: "The stationary and rotating equisignal beacon" [Bellini-Tosi, goniometer, Telefunken Compass, A/N fixed-course, tests at McCook Field / Dayton, and Wilbur Wright Field, loop crossing-angle effects], W. H. Murphy, L. M. Wolfe, in "SAE Transactions", Vol. 21, Part II, 1926, pp. 979-1015.
• Ref. 229P: articles about Australian "Marconi" Radio Range, Lorenz/AWA beams & ILS
• Ref. 229P1: "First radio beacon in Australia opened by the Minister for Defence", p. 3 in "The Radiogram - The Staff Journal of the Amalgamated Wireless (Australasia) Ltd.", Vol. III, no. XIII, July 1936. Source: worldradiohistory.com, retrieved 15 June 2020.
• Ref. 229P2: p. 128, 148, 149 in "Air Crash: the story of how Australia's airways were made safe, Vol. 1 - 1929-1939", Macarthur Job, Aerospace Publications Australia (publ.), 1991, 169 pp.
• Ref. 229P3: "Wireless - Radio for aircraft" [equisignal beacons should be established], in "The Sydney Morning Herald", Vol. 100, 7 Feb 1930, p. 5.
• Ref. 229P4: "Radio beacon - First in Australia - Opened near Mascot - Range up to 200 miles", in "The Sydney Morning Herald", Vol. 106, 28 April 1936, p. 10.
• Ref. 229P5: "Radio beacons - Air Board perplexed" [new beacon system (VHF) suggested, just before MW beacon tenders considered], in "The Age" (Melbourne), 26 January 1937, p. 9.
• Ref. 229P6: "Ultra Short Wave - Air-routes installation", [VHF beacons to be installed on main air routes], in "The Age" (Melbourne), 4 March 1937, p. 10.
• Ref. 229P7: "Radio to aid airmen- Six new beacons - Plans for network completed", in "The Sydney Morning Herald", Vol. 107, 29 May 1937, p. 17, 18.
• Ref. 229P8: "Aviation - Air beacons - Installation in Australia - Progressive radio" [Lorenz/Germany staff supervises installation of beacons; equipment imported and manufactured by AWA], in "The Sydney Morning Herald", Vol. 107, 4 December 1937, p. 16.
• Ref. 229P9: "Radio beam might have saved Kyeema - Evidence of expert - The beam was found satisfactory" and "Beacons tests - Plane chartered" [accident investigation; Lorenz VHF beacon at Essendon & Canberra ground test soon], in "The Age" (Melbourne), 3 November 1938, p. 13.
• Ref. 229P10: "Radio aids to flying - Tests begin", in "The Sydney Morning Herald" [accident investigation; Lorenz & AWA receivers, VHF ], Vol. 108, 5 November 1938, p. 13.
• Ref. 229P11: "Kyeema disaster inquiry - Suitability of new beacons - World's best safety factors", in "The Age" (Melbourne), 5 November 1938, p. 32.
• Ref. 229P12: "Board's lack of plane - Many requests - Needed for beacon tests - Government's delay", in "The Sydney Morning Herald", Vol. 108, 8 November 1938, p. 8.
• Ref. 229P13: "Air beacons - "We lead the world" - Captain Johnston at Kyeema Inquiry" [accident investigation; MW vs VHF beacons, AWA experimental receiver, Philips "blind landing" beacon system did not meet Civil Aviation Board specs], in "The Sydney Morning Herald", Vol. 108, 24 November 1938, p. 12.
• Ref. 229P14: "Airlines and activities - First radio beacons to-day - Sidney-Brisbane route" [all beacons along route operational this day], in "The Age" (Melbourne), 3 April 1939, p. 9.
• Ref. 229P15: "Radio beacons - First manufacture in Australia", in "The Sydney Morning Herald", Vol. 109, 7 April 1939, p. 8.
• Ref. 229P16: "Airlines and activities - Beacon made in Australia - Useful development" [VHF beacons, first at Sydney/Kingford-Smith, equipment designed & made by AWA, 90 ft steel tower], in "The Age" (Melbourne), 13 April 1939, p. 9.
• Ref. 229P17: "Air navigation aids - Four beacons at work" [8 of 10 beacons tested, 4 of which already operational], in "The Sydney Morning Herald", Vol. 109, 7 June 1939, p. 21.
• Ref. 229P18: "History of radio beacons - Delays in operation - Evidence on tests and experiments" [Lorenz & Telefunken beacons, STC, suitability of German receivers], in "The Age" (Melbourne), 4 November 1938, p. 7.
• Ref. 229P19: "Fault in air beacons - Steel towers may go - Long series of delays", in "The Sydney Morning Herald", Vol. 109, 28 November 1939, p. 12.
• Ref. 229P20: "Australia perfects radio guide" [claims Australian scientists first in world to perfect DME], in "The Sydney Morning Herald", Vol. 118, 8 January 1949, p. 3.
• Ref. 229P21: "Radio aids for safer flying" [Radio Ranges, ILS, DME], in "The Sydney Morning Herald", Vol. 120, 19 September 1950, p. 2.
• Ref. 229Q: "Principles of Aeronautical Radio Engineering", P.C. Sandretto, McGraw-Hill Book Co. (publ.), 1^st ed., 1942, 424 pp. Source: us.archive.org [file size 20 MB], retrieved 15 June 2020.
• Chapters II-VIII: "The Radio Range", "The Ultra-High-Frequency Radio Range", "Aircraft Direction Finders", "Markers", "Instrument Landing", "Absolute Altimeters", "Direction Finding from Ground Stations".
• Key words: radio ranges; derivation of loop antenna field-strength pattern; goniometer; apparent/phantom loop vs. physical/true loop; course-shifting & -bending; TL range antenna system; "night effect" elimination; Simultaneous Radio Range (beacon + voice); Visual Radio Range; reed instruments; 12-course (never in service); UHF radio range; shore-effect (dielectric constant & soil conductivity); multiple/split courses (altitude dependent); TL tower; Alford Loop; Visual 2-Course Range (90/150 Hz modulation + 1020 Hz A/N quadrant ID & station passage); RCA VHF Omni-directional range (VOR) being developed (1942), preceded by LW omni with rotating goniometer + north signal; cardioid pattern; ILS (Lorenz, Bureau of Standards, United-bendix, CAA-ITT, Washington Institute of Technology, CAA-MIT), Dingley leader cable, altimeters (sonic, capacitive, radio).
• Ref. 229R: US Dept. of Commerce, bi-weekly Air Commerce Bulletins (ACB) 1929-1939, Aeronautics Bulletin (AB) 1936, monthly Civil Aeronautics Journals (CAJ) 1944-1950, Technical Development Reports (TDR), Technical Manuals (TM), Miscellaneous Publications (MP). Source ACB: hathitrust-org, source AB: hathitrust.org; source CAJ: hathitrust.org (1) and  hathitrust.org (2);  retrieved June-September 2020. Source TM: hathitrust.org, retrieved February 2021; [abstracts/summaries of all ACB & CAAJ articles below]
• Ref. 229R1: ACM, Vol. 1 (July-December 1929, January-June 1930) [abstracts / summaries] ‒
  No. 2 (July-'29), pp. 19-20, No. 3 (Aug-'29), p. 13, No. 4 (Aug-'29), pp. 5-11, 21-23, No. 5 (Sept-'29), pp. 10-11, No. 8 (Oct-'29), pp. 15-17, No. 10 (Nov-'29), pp. 1-3,  No. 11 (Dec-'29), pp. 11-12, 29, No. 12 (Dec-'29), p13, No. 13 (Jan-'30, pp. 19-20, No. 14 (Jan-'30), p. 18, No. 15 (Feb-'30), p. 18,  No. 16 (Feb-'30), pp. 14,  No. 18 (Mar-'30), p. 16,  No. 19 (Apr-'30), p. 15, No. 22 (May-'30), pp. 3-8, No. 23 (June-'30), pp. 5-6, No. 24 (June-'30), p. 9.
• Ref. 229R2: ACM, Vol. 2 (July-December 1930, January-June 1931) [abstracts / key words] ‒
  No. 4 (Aug-'30), pp. 79-87, No. 5 (Sept-'30), pp. 120-121, No. 8 (Oct-'30), pp. 201-203, No. 10 (Nov-'30), pp. 272-275, No. 14 (Jan-'31), pp. 366-367, 370-371, No. 15 (Feb-'31), pp. 393, No. 17 (Mar-'31), pp. 437-439, No. 20 (Apr-'31), pp. 526-529.
• Ref. 229R3: ACM, Vol. 3 (July-December 1931, January-June 1932) [abstracts / summaries] ‒
  No. 3 (Aug-'31), pp. 55-58, No. 4 (Aug-'31), p. 102, No. 8 (Oct-'31), p. 109, No. 15 (Feb'-32), pp. 361-365, No. 18 (Mar-'32), pp. 433-438, 440, 441.
• Ref. 229R4: ACM, Vol. 4 (July-December 1932, January-June 1933) [abstracts / summaries] ‒
  No. 2 (July-'32), pp. 33-45, No. 5 (Sept-'32), pp. 121-126,  No. 6 (Sept-'32), pp. 135-150, No. 11 (Dec-'32), pp. 260-264, No. 12 (Dec-'32), pp. 293-294, No. 17 (Mar-'33), pp. 424-426, No. 18 (Mar-'33), pp. 441-427, No. 19 (Apr-'33), pp. 467-469, 470-472, No. 21 (May-'33), pp. 525-529, No. 22 (May-'33), pp. 555-569.
• Ref. 229R5: ACM, Vol. 5 (July-December 1933, January-June 1934) [abstracts / summaries] ‒
  No. 1 (July-'33), pp. 3-7, 16, No. 5 (Nov-'33), pp. 127-133, No. 7 (Jan-'34), pp. 165-168, No. 8 (Feb-'34), pp. 202, No. 9 (Mar-'34), pp. 223-225, No. 11 (May-'34), pp. 265-271.
• Ref. 229R6: ACM, Vol. 6 (July-December 1934) [abstracts / summaries] ‒
  No. 3 (Sept-'34), pp. 55-59, No. 5 (Nov-'34), pp. 108, 109.
• Ref. 229R7: ACM, Vol. 8 (July-December 1936, January-June 1937) [abstracts / summaries] ‒
  No. 3 (Sept-'36), pp. 65-70, No. 4 (Oct-'36), pp. 83-93, No. 5 (Nov-'36, pp. 127-129, No. 8 (Feb-'37), pp. 169-175.
• Ref. 229R8: ACM, Vol. 9 (July-December 1937, January-June 1938) [abstracts / summaries] ‒
  No. 4 (Oct-'37, pp. 77-85, No. 5 (Nov-'37) , p. 119, No. 6 (Dec-'37), pp. 141-143, No. 8 (Feb-'38), pp. 189-191, No. 12 (June-'38), pp. 304-306.
• Ref. 229R9: ACM, Vol. 10 (July-December 1938, January-June 1939) [abstracts / summaries] ‒
  No. 4 (Oct-'38), p. 116, No. 12 (June-'39), p. 301.
• Ref. 229R10: AB, No. 24 (1936), "The federal airways system" [incl. airway operations, intermediate landing fields, optical airway beacons, radio range beacons (types RA, RL, MRA, MRL, ML), radio communication stations, weather service], U.S. Dept. of Commerce, Bureau of Air Commerce, 1 July 1936, 25 pp.
• Ref. 229R11: ACM, Vol. 11 (July-December 1939) [abstracts / summaries] ‒
  No. 5 (Nov-'39), pp. 121, 124, No. 6 (Dec-'39), pp. 155-157.
• Ref. 229R12: CAJ, Vol. 1 (1940)  [abstracts / summaries] ‒
  No. 3 (Feb-'40, pp. 37, 38, 52), No. 7 (Apr-'40, pp. 109-111, 156.
• Ref. 229R13: CAJ, Vol. 5 (1944) [abstracts / summaries] ‒
  No. 3 (Mar-'44, pp. 29, 39, No. 12 (Dec-'44), p. 140.
• Ref. 229R14: CAJ, Vol. 6 (1945) [abstracts / summaries] ‒
  No. 2 (Feb-'45), pp. 13, 17.
• Ref. 229R15: CAJ, Vol. 7 (1946) [abstracts / summaries] ‒
  No. 6 (June-'46), pp. 72, 78, No. 7 (July-'46), pp. 85, 95, No. 11 (Nov-'46), pp. 137, 142, 148, No. 12 (Dec-'46), p. 150.
• Ref. 229R16: CAJ, Vol. 8 (1947) [abstracts / summaries] ‒
  No. 3 (Mar-'47), pp. 30, 31, 33, No. 4 (Apr-'47, pp. 37, 44.
• Ref. 229R17: "Circuit design for low-frequency radio ranges" [general description, field intensity distributions, coupling system, antenna currents, phase between antenna pairs vs. course shift, equipment], Donald M. Stuart, "CAA Technical Development Report No. 23 (formerly CAA Technical Development Div. Report No. 8)", November 1939, 23 pp. Source; hathitrust.org, retrieved 26 June 2020.
• Ref. 229R18: "Visual-Aural Ranges and Omniranges", Bulletin No. 3 of "CAA Airways Operations Training Series", March 1949, 24 pp. Source: hathitrust.org, retrieved 26 June 2020.
• Ref. 229R19: "Flying the Omnirange", Department of Commerce,  Civil Aeronautics Administration, Aviation Information, June 1950. 24 pp. Source: hathitrust.org, retrieved 26 June 2020. Revised version was issued by the CAA as "Basic omnirange flying", February 1951, 9 pp.
• Ref. 229R20: "The status of instrument landing systems" [NBS, Lorenz system, Army Air Force, Washington Institute of Technology, Indianapolis, Transcontinental / Western Air / United Airlines, Bendix], William Elvin Jackson, Department of Commerce, Bureau of Air Commerce, Civil Aeronautics Authority, Safety and Planning Division, Technical Development Report No. 1 (formerly CAA Technical Development Report No. 1 (TDR 1), October 1937, 15 pp. Source: hathitrust.org, retrieved 1 July 2020. [Abstract]. Note: this article was also published in 1938 the Proc. of the I.R.E. (ref. 229L19).
• Ref. 229R21: "Preliminary report on a four course ultra-high-frequency radio range", J.C. Hromada, Dept. of Commerce, Bureau of Air Commerce, Safety and Planning Division, Technical Development Report No. 3 (TDR 3, formerly Report No. 3), January 1938, 7 pp., CAA reprint, 1940. Source: hathitrust.org, retrieved 1 July 2020.
• Ref. 229R22: "Geographical separation of Radio Range stations operating on the same or adjacent frequencies in the 200-400 kilocycle band", A.E. Harrison, U.S. Department of Commerce, Civil Aeronautics Authority, Technical Development Report No. 4, January 1938, 6 pp. Source: hathitrust.org, 16 January 2021.
• Ref. 229R23: "The Ultra-High-Frequency Aural Radio Range", J.C. Hromada, P.B. King, Part I of "Development of the Ultra-High-Frequency Radio Range", U.S. Dept. of Commerce, Civil Aeronautics Administration, Radio Development Section, Technical Development Division, Technical Development Report No. 42, June 1944, 15 pp.
• Ref. 229R24: "Testing of the UHF Radio Ranges and Towers", P.B. King, T.A. Kouchnerkavich, Part II of "Development of the Ultra-High-Frequency Radio Range", U.S. Dept. of Commerce, Civil Aeronautics Administration, Radio Development Section, Technical Development Division, Technical Development Report No. 43, July 1944, 40 pp. [file size: 34 MB]
• Ref. 229R25: "A Visual-Aural Ultra-High-Frequency Radio Range with Simultaneous Voice", Part III of "Development of the Ultra-High-Frequency Radio Range", U.S. Dept. of Commerce, Civil Aeronautics Administration, Radio Development Section, Technical Development Division, Technical Development Report No. 49, June 1945, 116 pp. [file size: 40 MB]
• Ref. 229R26: "Pilots' Radio Handbook" [incl. Visual Radio Range, Aural Radio Range, Omni Range / VOR, ILS], U.S. Dept. of Commerce, Civil Aeronautics Administration (C.A.A.), Technical Manual No. 102, September 1953, revised March 1954, 127 pp. [file size: 31 MB]
• Ref. 229R27: pp. 295-298 in "The tide of commerce and industry (1920-30)", Chapter V (pp. 221-298) in "Measures for Progress - A history of the National Bureau of Standards", Rexmond C. Cochrane, James. R. Newman (ed.), U.S. Dept. of Commerce, Miscellaneous Publication 275 (MP 275), 1966, 683 pp. Source: nist.gov, retrieved 19-Feb-2021.
• Ref. 229R28: "Airplane radio" [1921 NBS support to Army Air Service experiments with loops crossing at 45° for generating equisignal course], p. 68 in "Radio Communication", in "Annual Report of the Director Bureau of Standards to the Secretary of Commerce for the Fiscal Year Ended June 30, 1921", Dept. of Commerce, Miscellaneous Publication No. 47 (MP 47), 1921, 276 pp. Source: digital.library.unt.edu, retrieved 22 February 2021.
• Ref. 229R29: p. 172 in "Some activities and accomplishments", pp. 162-285 in "Standards Yearbook 1927" [covers 1926!] , Dept. of Commerce, Bureau of Standards, Miscellaneous Publication No. 77 (MP77), 12 February 1927, 408 pp. Source: nist.gov, retrieved 13 March 2021.
• Ref. 229R30: p. 76 in "Bureau of Lighthouses", pp. 74-76 in "Standards Yearbook 1928" [covers 1927!], Dept. of Commerce, Bureau of Standards, Miscellaneous Publication No. 83 (M83), 4 January 1928, 399 pp. Source: nist.gov, retrieved 13 March 2021.
• Ref. 229R31: "The development adjustment, and application of the Z-marker" (a higher resolution file is here, file size 43 MB), W.E. Jackson, H.I. Metz, Civil Aeronautics Authority Technical Development Report No. 14 (TDR-14, formerly Report No. 16, Safety & Planning Division, Bureau of Air Commerce, Dept. of Commerce), July 1938, 28 pp. Source: hathitrust.org, retrieved 9 April 2021.
• Ref. 229R32: "The development of fan-type Ultra-High-Frequency radio markers as a traffic control and let-down aid", Henry Irwin Metz, Civil Aeronautics Authority, Technical development Report No. 5 (CAA TDR-5; formerly Report No. 5, Safety & Planning Div., Bureau of Air Commerce, Dept. of Commerce), January 1938, 22 pp.
• Ref. 229R33: "The development of an improved Ultra-High-Frequency radio fan marker", P.D. McKeel, J.M. Lee, H.I. Metz, Civil Aeronautics Authority, Technical development Report No. 12 (CAA TDR-12, formerly Report No. 14, Safety & Planning Div., Bureau of Air Commerce, Dept. of Commerce)), June 1938, 22 pp.
• Ref. 229S: "American Aviation Heritage - Identifying and Evaluating Nationally Significant Properties in U.S. Aviation History, A National Historic Landmarks Theme Study", U.S. Dept. of the Interior, National Park Service, Rev. March 2011, 320 pp. Source: npshistory.com, retrieved 20 June 2020. [pdf]
• Incl.: College Park Airfield/MD (pp. 84-87, p. 261), Army's McCook Field in Dayton/OH (p. 54, 67, 71, 125, 134, 267; all facilities moved to Wright Field in 1927 and was then closed down), Wright Field (also near Dayton/OH, later renamed Wright-Patterson AFB; pp. 3-5, 125, 134-136), Bellefonte/PA Air Mail Field (p. 84, 85, 271; NBS 4-course range test site), Mitchel Field near Garden City/NJ (p. 168)].
• Ref. 229T: articles/books about radio beacons developed and/or installed in France
• Ref. 229T1: "Navigation radioélectrique (principe des appareils)" ["Radio Navigation (principles of the equipment)"; D/F, rotating loop, rotating beacons with radio goniometer, course-beacons, Lorenz & L.M.T. landing systems, ], Ministère des Travaux Public et des Transports, Secrétariat Général à l'Aviation Civile et Commerciale, Section des Instructions Aéronautique, preliminary edition, 1944, 44 pp. Source: calameo.com, retrieved 3 July 2020.
• Ref. 229T2: "Les phares aéronautiques - France, Allemagne, États-Unis, Europe du Nord, 1910-1960" ["Aeronautical beacons - France, Germany, USA, northern Europe"], Collection Mémoire de l'Aviation Civile, Direction Générale de l'Aviation Civile (DGAC), 2018, 99 pp. Source: Ministère de la Transition écologique et solidaire / Mission Mémoire de l'Aviation Civile, retrieved July 2020.
• Ref. 229T3: "Chronique de la navigation aérienne" ["Chronicle of radio air navigation", file size: 30 MB], Jean Hubert, École Nationale de l'Aviation Civile (ENAC, National Civil Aviation School, Toulouse/France, publ.), 1987, 349 pp. Source: Ministère de la Transition écologique et solidaire / Mission Mémoire de l'Aviation Civile, retrieved December 2019. [Notes]
• Ref. 229T4: "Navigation radioélectrique (principe des appareils)" ["Radio navigation - principle of the systems"; radio-goniometer & error sources, automatic goniometer/DF, radio compass, omni-directional radio beacons, fixed & rotating course-beacons, radio altimeter, bad-weather landing methods & beacons, Lorenz], Ministère des Travaux Public et des Transports, Secrétariat Général à l'Aviation Civile et Commerciale, Section des Instructions Aéronautique, preliminary edition, 1944, 44 pp. Source: calameo.com, retrieved 3 July 2020.
• Ref. 229T5: "Phares lumineux ou radiophares?" ["Optical or radio beacons?"], P. Franck, in "L'Aéronautique - Revue mensuelle illustrée", Vol. 9, No. 100, September 1927, pp. 271-274. Source: Bibliothèque National de France (BNF) online library, retrieved 11 July 2020.
• Ref. 229T6: "Un important problème de la navigation áerienne : Le guidage des avions 1-2-3" ["An important problem in aerial navigation: the guidance of aircraft", Parts 1-3], M. Volkringer, in "Revue Aéronautique de France", Vol. 20, No. 3, March-April 1930, pp. 4-6; No. 4, April-May 1930, p. 7; No. 7, July-August 1930, pp. 5-6. Source: Bibliothèque National de France (BNF) online library, retrieved 11 July 2020.
• Ref. 229T7: "L'atterissage sans visibilité des avions par l'emploi des ondes ultra-courtes - 1" ["Aircraft landing without visibility by using ultra-short waves" - Part 1 of 3], Vol. 29, No. 7-8, July-August 1939, pp. 10-12. Source: Bibliothèque National de France (BNF) online library (the library does not hold issues of this magazine with the remaining part(s) of the article), retrieved 7 September 2020.
• Ref. 229T8: "Les radiophares d'atterrissage" ["Radio beacons for landing"], Paul Larivière, in "L'Aéronautique", Vol. 18, No. 207, August 1936, pp. 155-163. Source: Bibliothèque National de France (BNF) online library, retrieved 11 July 2020.
• Ref. 229T9: "Note sur les aériens et les diagrammes de rayonnement des radiophares de guidage à enchevêtrement / Notice concerning the aerials and the diagrams of radiation of the radio range beacons at interlocking signals" [article in both French & English], Yves Rocard, in "Bulletin de la Société Française Radio-Électrique (S.F.R.)", Vol. 11, No. 2, 2^nd Quarter 1937, pp. 33-60. Source: Bibliothèque National de France (BNF) online library, retrieved 11 July 2020.
• Ref. 229T10: "Les radiophares interférentiels S.A.D.O.D.-Aicardi" ["Directional radio beacons of the company Société des Ondes Dirigées (SADOD), system Aicardi], Paul Larivière, in "L'Aéronautique", Vol. 19, No. 219, August 1937, pp. 198-202. Source: Bibliothèque National de France (BNF) online library, retrieved 11 July 2020.
• Ref. 229T11: "Effets de diffraction affectant la signalisation des radioalignements" ["Effects of refraction (shore effect) on the signalling of radio course beacons"], Yves Rocard, in "Revue Scientifique", Vol. 78, No. 5-6, May-June 1940, pp. 267-272. Source: Bibliothèque National de France (BNF) online library, retrieved 11 July 2020.
• Ref. 229T12: "Un dispositif français d'atterrissage sans visibilité" ["A French device for blind landing"], in "Aviation Française", No. 138, 22 October 1947, p. 8. Source: Bibliothèque National de France (BNF) online library, retrieved 11 July 2020.
• Ref. 229T13: "L'atterrissage dans la brume" ["Landing in fog"], Henry Porra, in "Science et Vie", No. 356, May 1947, pp. 223-233. [ZZ method, Toulouse, SCS 51, GCA, CSF].
• Ref. 229T14: "Le temps des ingénieurs de la navigation aérienne - Mémoires techniques 1945-1985" ["The era of radio navigation engineers"; file size: 34 MB], Groupement des Ingénieurs de L'aviation Civile Rétraités (Bordeaux), 2013, 243 pp. Source: calameo.com, retrieved 4 October 2020.
• Ref. 229U: "Report on electronic systems of air navigation - "Technical and economic characteristics of LF/MF non-directional beacons, Standard Loran, Consol [Sonne-Consolan], Navarho, Decca, "GEE" system, LF/MF four-course radio range, VHF omni-directional range, Distance Measuring Equipment", Air Coordinating Committee, Air Traffic Control & Navigation Panel, Special Working Group No. 9; U.S. Dept. of Commerce, Office of Technical Services, March 1954, pp. Source: hathitrust.org, retrieved 1 July 2020.
• Ref. 229V: articles, books, and other material about the history of the U.S. DoC National Bureau of Standards and its beacons
• Ref. 229V1: "History and development of the Bureau of Standards radio beacon experiment station at College Park, Maryland", Robert W. Beckham, 18 December 1936, 40 pp. Records of the Phi Mu Fraternity, Special Collections, University of Maryland Libraries, University of Maryland, College Park. Source: archive.org, retrieved 3 July 2020. [Introduction]
• Ref. 229V2: pp. 293-298, 407 in "Measures for progress: A history of the National Bureau of Standards" [file size: 32 MB], Rexmond C. Cochrane, U.S. Dept. of Commerce, National Bureau of Standards, MP 275, 2^nd ed., 1974, 718 pp. Source: US National Institute of Standards and Technology (NIST),  accessed 3 September 2020. [pdf]
• Ref. 229V3: "The first radio beacon is inaugurated", photo of the interior of the Bureau of Standards beacon radio hut at College Park/MD/USA, with its director, George K. Burgess, 30 May 1927. Retrieved 19 February 2021.
• Ref. 229V4: Historic images in the Digital Archives of the National Institute of Standards and Technology (NIST, Gaithersburg, MD 20899). Records: Dials for blind landing aircraft (Aug. 1930), Blind landing system - 1 (Dec. 1930), Blind landing system - 2 (Dec. 1930), Interior of blind landing system (Dec. 1930), Landing beacon indicator and control panel (April 1930), Aids for blind landing of aircraft (July 1930), College Park field station (1926), Aircraft course indicators using two metal reeds, 1928. Accessed: June-August 2020.
• Ref. 229W: U.S. Dept. of Commerce and US Army Air Forces documents covering air navigation (incl. US radio range maps)
• Ref. 229W1: "Practical air navigation and the use of the aeronautical charts of the Department of Commerce", Thoburn C. Lyon, Special Publication No. 197, U.S. Dept. of Commerce, Coast and Geodetic Survey, 1935, 63 pp. [file size: 23 MB] [p. 36 - Radio Range chart] Source: hathitrust.org.
• Ref. 229W2: "Practical air navigation and the use of the aeronautical charts of the U.S. Coast and Geodetic Survey", Thoburn C. Lyon, Special Publication No. 197, U.S. Dept. of Commerce, Coast & Geodetic Survey, 2^nd ed. (1938), 204 pp. [p. 53 - Radio Range chart] [file size: 52 MB] Source: noaa.gov, accessed 21 July 2020.
• Ref. 229W3: "Practical air navigation", Thoburn C. Lyon, Civil Aeronautics Bulletin No. 24, U.S. Dept. of Commerce, Civil Aeronautics Administration (CAA), September 1940, 263 pp. [p. 97 - Radio Range chart] [file size: 49 MB]. Source: hathitrust.org, accessed 22 July 2020.
• Ref. 229W4: "Practical air navigation", Thoburn C. Lyon, 1945, 359 pp. [p. 200 - Radio Range chart] [file size: 112 MB] Source: hathitrust.org, accessed 23 July 2020.
• Ref. 229W5: "Instrument Flying: Advanced (with Radio Aids)" [incl. A/N Radio Ranges, Marker Beacons], U.S. Army Air Forces, Technical Order No. 30-100B-1, 15 January 1944, 80 pp. Source: aafcollection.info, accessed 23 September 2020.
• Ref. 229W6: "The Evolution of Instrument Flying in the U.S. Army", David M. McIntosh, Air Command and Staff College, Air University, Maxwell AFB, Student Report Nr. 88-1760, April 1988, 65 pp. Source: US Defence Technical Information Center, retrieved 7 October 2020.
• Ref. 229W7: "Civil Aviation and Facilities - Aerospace Education II", N.A. Orser, W.G. Glascoff, US Air Force Junior ROTC, "ED 068 290", 1969, 148 pp. Source: eric.ed.gov, retrieved 1 April 2021.
• Ref. 229X: "Characteristics of Radio Ranges, Elementary Radio Range flying, Instrument Approach Procedures, Radio compasses, Instrument landings and other development projects", Chapters III, IV, V, IX, and X in "Instrument and radio flying" [Radio Ranges, Instrument Approach Procedures, radio compasses, Busignies, Sperry-RCA ADF, Hegenberger, Lorenz, UHF Ranges, Air-Track, RTCA, Bendix System, Metcalf, Flighttray] Karl S. Day, Air Associates, Inc. (publ.), 1938, 284 pp. Source: hathitrust.org, retrieved 8 June 2021.
• Ref. 229Y: articles in popular radio & aviation magazines and newspapers, primarily 1920s-1930s
• Ref. 229Y1: "Radio beacons to aid air mail flyers", R.S. Winters, in "Radio Age", Vol. 7, Nr. 1, September 1927, pp. 21-24, 48. Source: worldradiohistory.com,, retrieved 23 February 2021.
• Ref. 229Y2: "Guiding airplanes by radio beacons", S.R. Winters, in "Popular Aviation", Vol. 1, Nr. 4, November 1927, pp. 23-26.
• Ref. 229Y3: "Landing of aircraft in fog by radio", H. Diamond, in "Electronics", Vol. 6, Nr. 6, June 1933, pp. 158-161. Source: worldradiohistory.com, retrieved 23 February 2021.
• Ref. 229Y4: "Airports and Airways" [radio beacon at Hadley Field], in "Aviation" (pre AvWeek), Vol. 23, No. 1, 29 August 1927, p. 486, 488. Source: us.archive.org, retrieved 24 February 2021.
• Ref. 229Y5: "Federal Airways", Charles Ingram Stanton, in "Radio News", Vol. 29, No. 6, June 1943, pp. 100, 101, 260, 266. Source: worldradiohistory.com, retrieved 1 April 2021.
• Ref. 229Y6: "Radio Ranges", Donald M. Stuart, in "Radio News", Vol. 29, No. 6, June 1943, pp. 126-129, 266, 272. Source: worldradiohistory.com, retrieved 1 April 2021.
• Ref. 229Y7: "Washington plans new radio beacon as aid to flyers" [Bureau of Standards, College Park/MD], in "The Baltimore Sun", Vol. 179, No. 85D, 23 August 1926, p. 7.
• Ref. 229Y8: "Radio beacon guides direction of planes - Army experts report recent experiment worked perfectly" [Army Signal Corps, Bureau of Standards, first beacon guided flight, from Ford Airport to McCook Field], in "The Evening Sun" (Baltimore/MD)", 25 March 1927, p. 40.
• Ref. 229Y9: "Radio beacons will serve planes as direction guides" [Bureau of Standards, College Park/MD, airplane radio telephone, 6 beacon station established or under construction], in "The Hartford Courant", Vol. XC, 22 May 1927, p. 75.
• Ref. 229Y10: "Radio soon practical for airplane service" [College Park/MD, Bellefonte/PA, McCook Field in Dayton/OH; Ford Motor Co. Field Dearborn/MI & Chicago/IL, Hadley Field/NJ], in "The Pittsburgh Press", 5 June 1927, p. 51.
• Ref. 229Y11: "First radio beacon dedicated" [College Park/MD], in "Kenosha Evening News", Vol. XXXIII, No. 194, 10 June 1927, p. 29
• Ref. 229Y12: "The first radio beacon is inaugurated" [photo; College Park/MD, Bureau of Standards], in "Fort Worth Star-Telegram", Vol. XLVII, Nr. 146, 26 June 1927, p. 12.
• Ref. 229Y13: "Radio beacons guide flyers across continent" [radio beacon telephone; photo; College Park/MD, E.Z. Stowell, P.W. Dunmore, H. Pratt, C.B. Hempel, J.H. Dellinger, Bureau of Standards], in "The Hartford Courant", Vol. XC, 26 June 1927, p. 68.
• Ref. 229Y14: "Radio beacons for air-travel over the seas" [photo; J.H. Dellinger, Bureau of Standards, chain of radio beacons across the ocean], in "The Capital Times" (Madison/WI), Vol. 19, No. 18, 2 July 1927, p. 4.
• Ref. 229Y15: "U. S. scientists responsible for radio beacon" [photo; F. Dunmore, J.H. Dellinger, H. Pratt; Bureau of Standards; College Park], in "Fort Worth Star-Telegram", Vol. XLVII, Nr. 202, 21 August 1927, p. 1.
• Ref. 229Y16: "Footnotes" [visual beacon, DoC, BoS, 8 years, College Park], in "Nebraska State Journal", 16 June 1928, p. 6.
• Ref. 229Y17: "Engineers told of government's work on aircraft radio" [1926 Air Commerce Act, Aeronautics Branch, BoS, 1926/27 BoS beacon stations], in "Chicago Sunday Tribune", 17 June 1928, p. 5
• Ref. 229Y18: "Radio beacon is now practical - Enables airmen to fly on course in any weather, engineers say" [Doc, BoS 1921, aural & visual systems, receiving set, indicator], in "New Cambria Leader", Vol. XVI, Nr. 27, 31 August 1928, p. 2.
• Ref. 229Y19: "Flying conquers fog" [BoS, cockpit instruments, reed indicator], James Stokley, in "Oakland Tribune", Vol. CX, No. 48, 17 February 1929, p. 72.
• Ref. 229Y20: "Will conduct "fog flying" radio tests - Efficiency of the aircraft radio beacon to be tried out by Army flyer" [Doolittle, reed instrument, College Park], Martin Codel, in "Great Falls Tribune", Vol. 43, 3 July 1929, p. 13.
• Ref. 229Y21: "Former government scientists carry on aviation research - Radio experts, victims of Economy Act, form institute to pursue navigation developments as private individuals" [BoS, Washington Institute of Technology, at College Park(MD)] in "The Evening Star" (Washington/DC), 13 October 1933, p. 17.
• Ref. 229Y22: "And now... Happy landings for the "blind-flying-"pilot" [combined instrument, light & radio beacons, BoS, TL], J.H. Williams, in "Salinas Index-Journal", Vol. XLIX, 4 November 1933, p. 9.
• Ref. 229Y23: "Landing planes by radio in fog", Keith Wyatt, in "The Baltimore Sun", Vol. 37-D, 4 April 1937, pp. 98, 99.
• Ref. 229Y24: "Medium-wave beacons at Croydon" [335 kHz 4-course radio range; Marconi built?], in "Flight", 26 August 1937, p. 216.
• Ref. 229Z: articles and other material about the Henry Ford A/N radio beacons
• Ref. 229Z1: photos from the digital collection expert set of The Henry Ford, accessed 15 February 2021 - "Radio Beacon Transmitting Station and Antennas at Ford Airport, 10 September 1926" (image THF123653); "Radio Station "WFO" License for Operating the Ford Aircraft Radio Beacon, 26 October 1926" (image THF255154); "Detail of Goniometer Used inside the Radio Beacon Transmitting Station at Ford Airport, 10 September 1926" - (image THF99457), "Equipment Inside the Radio Beacon Station Building at Ford Airport, March 16, 1927" (image THF255074; goniometer motor drive & scale).
• Ref. 229Z2: "Ford Airways complete year's flight; no accident during entire year" [Ford air transport service started 13 April 1925, between Ford Airport at Dearborn/MI & Chicago/Maywood Field; 1 July 1925: between Detroit/MI & Cleveland/OH], in "Ford News", Vol. VI, No. 13, 1 May 1926, pp. 1, 8.
• Ref. 229Z3: "Ford Airways Daily Flight Report" entry of 8 November 1926: 2:25 hr / 230 miles beacon test flight Dearborn-Chicago with Eugene Donovan as "radio man".
• Ref. 229Z4: "Ford radio beacon for airplanes", in "Ford News", Vol. VII, Nr. 10, 15 March 1927, p. 1.
• Ref. 229Z5: "Guiding aerial flight by radio beacon - A process applied to commercial aviation on the Ford Airlines", in "Ford News", Vol. VII, Nr. 12, 1 April 1927, pp. 4, 5.
• Ref. 229Z6: "Ford plane with tour is winged laboratory - Is testing radio beacon, 500-mile telegraphic unit, and broadcast receiving set", in "Ford News", Vol. VII, Nr. 17, 1 July 1927, p. 1, 6.
• Ref. 229Z7: "Plane radio is efficient - In touch with land constantly on tour" [3rd National Air Tour; Ford Co. trimotor equipped with beacon radio equipment, mentions 5 beacons incl. Ford Co. beacon at Dearborn/MI], in "Ford News", Vol. VII, Nr. 19, 1 August 1927, p. 1.
• Ref. 229Z8: "First radio-directed flight" [10 Feb 1928: first official beacon-guided point-to-point flight - Dearborn/MI (Ford) to McCook Field (Army) ], in "Ford News", Vol. VIII, Nr. 6, 1 February 1928, p. 19.
• Ref. 229Z9: "The radio beam - Aviators depend on an invention developed by an automobile company", in "Ford News", Vol. XX, November 1940, p. 247, 262.
• Ref. 229Z10: "Radio beacon used by commercial airplane", William F. Gilmore, in "U. S. Air Services", Vol. XII, Nr. 3, March 1927, p. 15.
• Ref. 229Z11: "The new Ford transport", A.M. Jacobs, p. 68 in "Air Corps News Letter", Vol. XI, No. 3, 10 March 1927. Source: media.defense.gov, retrieved 19 February 2021.
• Ref. 229Z12: "1^st with a radio beam for planes!", 1-page Ford Co. advertising in "Boy's Life - For All Boys" magazine, May 1945, p. 19; on p. 12 in "Life", 5 February 1945; on p. 33 in "Popular Science", January 1945.
• Ref. 229Z13: pp. 204-207 in "Henry Ford: His life - His work - His genius", William Adams Simonds, Floyd Clymer (publ.), 1946 (revised ed.), 365 pp. Source: us.archive.org, retrieved 19 February 2021.
• Ref. 229Z14: "Aircraft Radio Beacon" chapter 10 (pp. 97-100) in "Beyond the Model T - The other adventures of Henry Ford", Ford R. Bryan, Wayne State University Press (publ.), revised edition, 1997, ISBN 0-8143-2682-X, 232 pp.
• Ref. 229Z15: "Ford Airport Hangar", National Register of Historic Inventory - Nomination Form, U.S. Dept. of the Interior, National Park Services, 10 April 1985, 25 pp. Source: catalog.archives.gov, retrieved 15 February 2021. [file size 25 MB] 
• Ref. 229Z16: recommended website "Flying the beams - The history of the Low Frequency Radio Range, aviation's first radio navigation system and other early radio navigation systems through the mid-20th century", Doug Davis, 2021. Accessed April 2021.
• Ref. 229Z17: "How the Ford radio beacon station changed aviation", YouTube video, accessed 15 February 2021.
• Ref. 229Z18: "Lansing Municipal Airport", 4 pp. in "Forgotten Chicago Airfields", Nicolas C. Selig, The History Press (publ.), 2014, 128 pp.
• Ref. 229Z19: "Ford Motor Company" [renewal of license for experimental radio stations W8XC, W9XH, W8XE], pp. 150-153 in "Decisions, reports, and orders of to Federal Communications Commission of the United States - July 1934 - July 1935 - Volume 1", Federal Communications Commission Reports, Federal Communications Commission, 1936, 338 pp.
• Ref. 229Z20: "Radio beacon guides Dayton Ford plane" [first beacon guided flight Ford Airport Dearborn/MI, McCook Field, Dayton/OH], in "St. Joseph Herald-Press" , 11 February 1927, p. 5
• Ref. 229Z21: "Radio beacon control invented" [Ford-Hammond Airport, Dearborn Field], in "The Lake County Times", Vol. XXI, No. 212, 14 April 1927, pp. 1, 21.
• Ref. 229Z22: "New radio beacon for Ford Airport at Lansing" [A/N/T beacon, Lansing & Detroit], in "The Lake County Times", Vol. XVIII, No. 14, 5 May 1928, p. 1.
• Ref. 229Z23: "Model airport opened by Ford" [Detroit, paved runways + taxi ways + aprons], in "The Sunday Star" (Washington/DC), No. 1231, 21 October 1928, p. 72.
• Ref. 229Z24: "Ford radio beacon hearing ordered - Company must show need of continuing service", in "The Detroit Free Press", Vol. 101, Nr. 9, 13 May 1931, p. 9.
• Ref. 229Z25: "Ford engineers designed, built radio beacon - Round-the-world airways system completed by Australia-India link" [Army Air Service fall 1926, BoS, Ford radio range], in "The Daily Republican" (Monongahela/PA), Vol. 98, Nr. 13, 9 June 1944, p. 5.
• Ref. 229Z26: "Radio beacon aids dirigible on flight" [Ford Airport], in "The Sacramento Bee", Vol. 140, No. 22,803, 20 November 1926, p. 40.
• Ref. 229Z27: "Radio beacons test at Ford airport", in "The New York Times", 27 February 1927, Section XX, p. 18.
• Ref. 230: German, British, US WW2 RDF, radio-navigation systems, and associated jamming systems / countermeasures
• Ref. 230A: p. 42 in "The Secret War", Brian Johnson, Pen and Sword (publ.), 2004, 352 pp. [pdf, file size 50 MB] See note 1
• Ref. 230B: Table 1 in "Verfahren und Anlagen der Funkortung" ["Radio-navigation methods and installations"], W. Stanner, in "Elektrotechnische Zeitung (ETZ)", Ausgabe A, Vol. 75, Nr. 13, 1 July 1954, pp. 438-442. [circular LoP, hyperbolic LoP, Consol, Consolor, Decca, Loran, range of various systems incl. "Erika", "Erich", "Hermes/Hermine", and "Mond"]
• Ref. 230C: articles and books about the Battle of the Beams
• Ref. 230C1: "Pulling the crooked-leg", R.V. Jones, in "New Scientist", 23 February 1978, pp. 493-496.
• Ref. 230C2: "Milestones - Battle of the Beams", Carlo Kopp, in "Defence Today", January/February 2007, pp. 76, 77. [pdf]
• Ref. 230C3: "The Battle of the Beams - Part 1-3", D.V. Pritchard (G4GVO), in "Practical Wireless", Vol. 64, No. 1, Issue 970, January 1989, pp. 43-47; No. 2, Issue 971, February 1988, pp. 46-49; No. 3, Issue 972, March 1988, pp. 30-34. Source: worldradiohistory.com, accessed 1 September 2020. Also published as "The Battle of the Beams - Part 1-3", D.V. Pritchard (G4GVO), in "Ham Radio Magazine", June 1989, pp. 29-38; August 1989, pp. 20-29; October 1989, pp. 53-61. Source: worldradiohistory.com, accessed January 2014.
• Ref. 230C4: "Battling the Radio beams", "Part 1: Headache and Aspirin" and "Part 2: Bromide, Domino and Benjamin", Bruce Taylor (HB9ANY), in "RadCom Magazine", Radio Society of Great Britain (RSGB), Vol. 96, No. 5, May 2020, pp. 80-82, and Vol. 96, No. 5, June 2020, pp. 82-84. Source: researchgate.net, retrieved September 2022.
• Ref. 230D: books & articles by Reginald Victor Jones (R.V. Jones)
• Ref. 230D1: "Most Secret War" (e-book version), R.V. Jones, Hamish Hamilton (publ.), 1978, 576 pp., ISBN 10: 0241897467. See note 1. For the US American market, this book was published under the title "The Wizard War - British Scientific Intelligence 1939-1945", Coward, McCann & Geoghegan (publ.), 1978, 614 pp., ISBN 10: 0698108965. It can be read on-line at archive.org. Chapter 11 & 16 (Crooked Leg / Knickebein) are here, Chapter 17 & 21 (X-System, Y-System) are here. See note 1.
• Ref. 230D2: "Scientific Intelligence", R.V. Jones, 12 February 1947 lecture, "CIA Studies in Intelligence" Vol. 6, No. 3 (Summer 1962), pp. 55-76. Source: cia.org, accessed 12 August 2020. This is a slighly edited version of the original 12 February 1947 lecture, as first published in "Journal of the Royal United Services Institution", nr. 42, August 1947, pp. 352-360.
• Ref. 230D2: "Navigation and War" [incl. magnetic compass 2400 BC, WW1, X, Y, Knickebein, G/GEE, Oboe, G-H], R.V. Jones in "Journal of Navigation", Vol. 28, Iss. 1, January 1975, pp. 1-24. Source: en.booksc.org. [pdf, See note 1]
• Ref. 230E: "The Secrete War", 7-part BBC/Imperial War Museum (IWM) TV broadcast series from 1977 [available on DVD and some episodes also on YouTube)]
• Ref. 230E1: episode 1: "The Battle of the beams" (radio navigation beams used by the Germans for more accurate bombing, and the British countermeasures).
• Ref. 230E2: episode 2: "To see a Hundred Miles" (radar).
• Ref. 230E3: episode 3: "Terror Weapens" (the V1 and V2).
• Ref. 230E4: episode 4: "If..." (inventions that never became operational, or were delayed, imagining what could have happened if they had been).
• Ref. 230E5: episode 5: "The Deadly Waves"(magnetic mines and degaussing measures).
• Ref. 230E6: episode 6: "Still Secret" (Bletchley Park and the Enigma Code, including the Colossus computer).
• Ref. 230E7: episode 7: "The Battle of the Atlantic" (1978).
• Ref. 230F: articles about the X-Verfahren ("X-Procedure), X-Gerät ("X-Equipment"), Y-Verfahren ("Y-Procedure"), Y-Gerät ("Y-Equipment"); this Y-navigation method is not to be confused with the "Y" fighter-guidance method (incl. Y-Peiler ("Y-D/F system") which is also referred to as "Y-verfahren", nor with the British radio monitoring/intercept Y-Service.
• Ref. 230F1: pp. 48-49 (X-Gerät, Y-Gerät) in "German Radio Communication Equipment", US War Department Technical Manual, TME 11-227, June 1944, 61 pp.
• Ref. 230F2: "Fliegerhorst Köthen" ["Köthen airfield"], source: Militärhistorisches Museum Anhalt, accessed 11 August 2020. [pdf]
• Ref. 230F3: pp. 14-27 in "The First Pathfinders - The Operational History of Kampfgruppe 100, 1939-1941", Kenneth Wakefield, William Kimber (publ.), 1981, 265 pp.
• Ref. 230F4: pp. lxx-lxxiv in "The Bombing War: Europe, 1939-1945", Richard Overy, Penguin Books Ltd. (publ.), 2014, 852 pp. (published 2013 by Allan Lane, published 2015 as "The Bombers and the Bombed: Allied Air War Over Europe, 1940–1945")
• Ref. 230F5: "Der gezielte Blind-Bomben-Wurf - Die deutsche Lösungen: Das X-verfahren, Das Y-verfahren (Kampf)" ["The targeted blind bomb drop - The German solutions: the X-Procedure, the Y-procedure"], Heinrich Pusch (Oberst a.D. (Colonel, retired); Gruppenkommandeur Kampfgruppe 100 in 1939, Kommandeur Luftnachrichten-Regiment 31 in 1941 and Ln-Regiment 56 in 1943], date unknown (but after 1949/50, based on references to volumes of Winston Chruchill's memoires published in 1949 & 1950, see ref. 230F6 & 230F7 below), 71 pp. [file size: 57 MB; a good-but-lower resoluton file is here 16 MB]. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. ZA 3/402a, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230F6: "The Wizard War", Chapter XIX (pp. 337-352) in "Alone", Book II in "Their Finest Hour" [file size: 29 MB], Vol. II (of 6) of "The Second World War", Winston S. Churchill, Houghton Mifflin Co. (publ.), 1949, 836 pp. Source: readerssection.com, accessed 30 December 2021.
• Ref. 230F7: "The offensive in the Aether", Chapter XVI (pp. 248-259) in "The Onslaught of Japan", Book I in "The Hinge of Fate" [file size: 23 MB], Vol. IV (of 6) of "The Second World War", Winston S. Churchill, Houghton Mifflin Co. (publ.),1950, 476 pp. Source: readerssection.com, accessed 30 December 2021
• Ref. 230F8: "Das Y-verfahren. Eine Weiterentwicklung des X-Verfahrens. Erdacht von Dr. Ing. Hans Plendl, 1940 Flieger-Oberstabingenieur bei der Erprobungsstelle der Luftwaffe Rechlin/Mecklb." ["The Y-Procedure. An evolution of the X-Procedure. Conceived by Hans Plendl, 1940, Pilot – Senior Staff Engineer at the Luftwaffe test center at Rechlin/Mecklenburg"], 32 pp. Source: Bundesarchiv (BArch) Freiburg/Germany (Signatur) file nr. ZA 3/402a, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230F9: "I./K.G.66 - Kurzer Abriss der technischen und taktischen Einsatzgrundlagen der I./K.G.66 (Zielfindergruppe West) in verschiedenen Kriegsphasen" ["Short overview of technical and tactical operationprinciples of No. 1 Group of Kampfgeschwader 66 (Pathfinder Group West)"], [keywords: target finding & marking; Ju-88 S, Ju-188 E; Vannes, Poix, Le Bourget; I./K.G.100; X-Verfahren, Y-Verfahren, Egon, 1324/Truhe-Verfahren; detailed list of I./K.G.66 aircraft/crew losses 30-May-1943 - 11-Apr-1945], Hans Herbestreit, ca. 1970, 14 pp. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL 10/638, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230G: Chapter II and III in "R. V. Jones and the Birth of Scientific Intelligence", James Martinson Goodchild, PhD thesis, University of Exeter, March 2013, 640 pp. [pdf] Accessed 12 May 2019.
• Ref. 230H: "Electronic Warfare and the Night Bomber Offensive", Rob O'Dell, pp. 97 - 117 in "Air Power Review", Royal Air Force, Volume 10, Number 1, Spring 2007.
• Ref. 230J: "Radio Navigation Systems for Aviation and Maritime Use — A Comparative Study" [RDF, Consol/Consolan, Navaglobe, VOR, VORTAC, VOR/DME, Navarho/Navarho-H/-HH/-Rho, Decca, Standard Loran (Loran-A), Loran-C, Radio Mesh System], W. Bauss (tech ed.), Advisory Group for Aeronautical Research and Development (AGARD), North Atlantic Treaty Organization (NATO), AGARDOgraph 63, Pergamon Press, 1963, 232 pp. Translation of the German publication "Funkortungssysteme für Luft- und Seefahrt - Eine vergleichende Gegenüberstellung", Verkehrs- und Wirtschaftsverl. Dr. Borgmann (publ.). [pdf, file size 58 MB]. The following are articles taken from this book.
• Ref. 230J1: "Radio Direction-Finding on Board Aircraft and Ships", W.T. Runge, pp. 19-28.
• Ref. 230J2: "Consol and Consolan", Ernst Kramar, pp. 29-39.
• Ref. 230J3: "VOR-System", K. Bärner, pp. 43-57.
• Ref. 230J4: "Decca". H. Lueg, pp. 81-101.
• Ref. 230J5: "Standard-Loran", Ernst Kramar, pp. 113-118.
• Ref. 230K: articles about Elektra, Sonne, Consol/Consolan, Elektra-Sonne, Mond
• Ref. 230K1: "The Navigational Beam System "Elektra-Sonne" [Elektra, Sonne, Elektra-Sonne, Mond; complete German description, short translated summary in English], Otto von Heil, FIAT Final Report No. 1105, Field Information Agency Technical (FIAT), US Office of Military Government for Germany, 17 June 1947, 177 pp. Source: www.cdvandt.org. Accessed: March 2019.
• Ref. 230K2: "Funknavigation, Elektra, Sonne, Mond, Stern, Erika", J. Goldmann (Lorenz), Vorträge vor Fernmelde-Ingenieuren der Luftwaffe - Luftnachrichtenschule Halle (Saale) [Luftwaffe Signals School], February 1944, 22 pp. [file size: 25 MB]. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) RL 2-V/48, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230K3: "Sonne Planungen" ["Planning of Sonne sites"; mentions Sonne station Liebau, Sonne stations 12 (Warsaw) & 23, Großsonne station 32 (Danzig), and new Sonne site near Oppeln], Luftnachrichten telegram, dated 29 July 1944, signed by Capt. Franz, 1 p. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) RL 2-V/6, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230K4: "Consol - Beacon Direction Finding system of high accuracy" [Consol, Sonne, SBA], John E. Clegg, in "Wireless World", Vol. 52, No. 7, July 1946, pp. 233-235. Source: worldradiohistory.com, retrieved 6 January 2021.
• Ref. 230K5: "CONSOLAN - WHAT IS IT? New navigation aid for small boats needs only a surplus long-wave receiver, and some simple modifications you can make", Elbert Robberson, in "Radio-Electronics", March 1961, pp. 54-57. Source: worldradiohistory.com, retrieved August 2022.
• Ref. 230L: "Radio vs. U-boat" - An account of the part played by radio in the Battle of the Atlantic", G.M. Bennet, in "Wireless World", Vol. 52, No. 12, December 1946, pp. 408-411. Source: worldradiohistory.com, retrieved 6 January 2021.
• Ref. 230M: "Demonstrations of Radio Aids to Civil Aviation: Technical Descriptions of Radio Aids Demonstrated in the United Kingdom on Behalf of P.I.C.A.O during September 1946" [Consol, Post Office Position Indicator (POPI), Automatic DF (Radio Compass), weather radar, Gee with L & θ indicator, Decca, Rebecca Mk II & IV + Orbit Computer, VHF Omni-directional Radio Beacon(ORB), VHF Rotating Beacon, VHF Cathode Ray DF (CRDF), Airfield Control radar (ACR), SCS-51, Airfield Surface Movement Indicator (ASMI), BABS Mk II, radio altimeter slot antenna, GEE/BABS/Rebecca trainers, H2S/ASV trainers], Great Britain, Ministry of Civil Aviation, Provisional International Civil Aviation Organisation, H.M. Stationery Office, 1946, 84 pp. Source: chingchic.com, retrieved 5 January 2021. [file size: 25 MB]
• Ref. 230N: articles about VHF rotating-phase navigation systems, "UKW-Phasendrehfunkfeuer",  VOR, Erich
• Ref. 230N1: "An Omnidirectional Radio-Range System - Part I & II" [VOR], David G.C. Luck, in "RCA Review", Vol. VI, Nr. 1, July 1941, pp. 55-81, Vol. VI, Nr. 3, January 1942, pp. 344-369. Source: worldradiohistory.com, retrieved 25 October 2020.
• Ref. 230N2: "Omnirange = Air Safety", Samuel Freedman, in "Radio Electronics", February 1951, pp. 24-26. Source: worldradiohistory.com, retrieved 27 January 2021.
• Ref. 230N3: "An omnidirectional Radio Range system - Part I &Part II", D.G.C. Luck, in "RCA Review", Vol. VI, No. 1, July 1941, pp. 55-81, and Vol. VI, No. 3, January 1942, pp. 344-369. Source: worldradiohistory.com, retrieved 11 April 2021.
• Ref. 230N4: "The CAA VHF Omnirange", H.C. Hurley, S.R. Anderson, H.F. Keary, Civil Aeronautics Administration, Electronics Div., Technical Development & Evaluation Center, Technical Development Report No. 113 (CAA TDR-113), January 1949 (published June 1950), 65 pp.
• Ref. 230P: original correspondence of the Director General of Luftwaffe Signals Corps (General Nachrichtenführer). Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) RL 2-V/5, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230P1: "Anruf Gen.Martini wegen Erstellung Boden-Truhe West" [telephone call with General Martini regarding construction of Boden-Truhe West]. Letter/telegram from Gen. Nachrichtenführer (1.Abt.II), addressed to Chef. der Ln.Inspektion. Letter ref. OKL Gen.Nafü. Nr. 10 955/44 g.Kdos. (1. Abt.II). Letter is dated 18 June 1944. Letter states that due to current situation, the forward-looking Boden-Truhe West station will not be constructed and construction of the rearward-looking Boden-Truhe West station will be accelerated, using transmitters of the prior. The planned transmitters will be transported from France, but with trucks/lorries (wood gas) instead of by rail.
• Ref. 230P2: "Fernmündliche Rücksprache Major Kluge - Hptm. Gottschalk am 30.6.44" [telephone conversation Major Kluge - Captain Gottschalk]. Letter from Gen.Nafü (1.Abt.), addressed to Lfl.Kdo. 3 - Höh.Nafü, General der Navigation, and General der Kampfflieger. Letter ref. OKL Gen.Nafü. Nr. 11 092/44 g.Kdos. (1. Abt.II). Letter dated 8 July 1944. Letter states that, due to operational and test reasons, construction of radio navigation stations "Komet 2 (Laharie)", "Komet 3 (Labouheyre), and "Dora 2 (Morlaix) cannot be finished. Due to failure of "Erika 2 (Cherbourg)", the "Erika" system can no longer be used in the West. Therefore, "Erika 1 (Boulogne)" can be dismantled and parts (transmitter etc.) be secured.
• Ref. 230P3: "Sender for Bodentruhe" [transmitters for Truhe ground station]. Letter from Gen.Nafü (1.Abt.), addressed to Gen.Nafü/Ln.Insp (5.Abt/6.Abt). Letter is dated 8 July 1944. Letter describes allocation of 3 "Feuerstein" transmitters instead of "Feuerzange" transmitters to "Bodentruhe West", also mentions 3 "Merkur" transmitters are to be modified for "Bodentruhe West", schedule for delivery of additional "Merkur" and "Feuerstein" transmitters to be provided.
• Ref. 230P4: "Abschalten von Rundfunksendern." [Shutdown of (public) radio broadcast transmitters]. Letter from OKL.Gen.Nachrichtenführer. Letter ref. 11 987/44 geh. (1.Abt.II). Letter is dated 2 July 1944. Letter states that, as agreed with OKW and RPromin [Reichs Propaganda Ministerium], the request for shutting down radio broadcast transmitters during jamming/interference of radio beacons for day & night fighters, is denied. Reasons given by RPromin: 1) the current regulations already imply large scale shutdowns, further reduction is unacceptable for the propaganda, 2) the population interprets shutdowns as sign of imminent air raids. Shutdown for other reasons would cause unrest, and 3) Broadcast transmitter frequencies are fixed. If broadcast transmitters interfere with radio beacons or other services, Lfl.Kdo. must make sure that those services use other frequencies. As in other Luftflotten regions, restriction of radio beacons improves spread of utilized frequencies. Note: the signature part of the letter contains "- Robinson 2 -". This code name refers to a special trainset at the disposal of the Gen.Nafü.
• Ref. 230Q: articles about Knickebein
• Ref. 230Q1: "Knickebein - ein «Leitfaden» der Luftwafe (Wehrmacht)" ["Knickebein - a "guide line" of the Luftwaffe"; general description and site visits of all Kn locations except Kn-1, Kn-5, Kn-11, Kn-13], web pages by christianCH, update of 5 April 2021. [pdf, file size: 19 MB] See note 1. [In Sept/Oct-2022 email exchanges, christianCH also provided me with dimensions he measured at Kn-8: concrete block (1.4x1.4 m), base plate (84x60 cm; 8 through-holes Ø 2 cm), the square plate on top of it (33x33 cm), and of the 2-step cylindrical pivot (Ø 14 cm with 4mm wall thickness and Ø 11 cm, respectively), and also of the width of the outer concrete ring at (large) Kn-12 (same as small Kn ring, and with radial grooves in top = depressions for cross-ties, no signs of rail attachments)].
• Ref. 230Q2: pp. 245-247 in "Gleichgeschaltet: Maulburg im Nationalsozialismus und die Rolle von Hermann Burte im Dritten Reich", Hansjörg Noe, Verlag Waldemar Lutz (publ.), 448 pp., ISBN 978-3-922107-09-5. [Extract]
• Ref. 230Q3: p. 16 of "Knickebein" thread in the forum of geschichtsspuren.de, post by ChristianCH on 30-Mar-2014. [Extract]
• Ref. 230Q4: p. 2, 3 in "Krigsminner 1940-45 i Klepp kommune" ["War memories 1940-45 in the Klepp municipality"], F. Ravndal, T. Ødemotland, A. Jakobsen, T. Erga, O. Håland, B. Bore, A. Hatteland, J. Sørbø, T. Reve, Laget (publ.), 1990, 8 pp. Source: Norwegian National Library, accessed 31 July 2020. [pdf]
• Ref. 230Q5: "Kontrollpunkten der Knickebein-Anlage 4 (Karten), dabei Gesamtübersicht der Kontrollpunkte, Bereich zwischen Kranenburg und Donsbrüggen" [file size: 34 MB] ["Radiation-pattern check points for Knickebein Nr. 4 ( = Kleve-Materborn) in the area between Kranenburg and Donsbrüggen"], 8 maps with check points marked by small red dots and red lines, some measured field strength values are written in green (dated January 1942), Kranenburg = ca. 13 km west of K4; Donsbrüggen = ca. 12 km northwest of K-4; 2 maps with check points in The Netherlands (just north & south of Groesbeek = ca. 18 km west of K-4)]. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) RL 19/6/64 - 19/6/84 (frmr. RL 19/537), used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230Q6: "Knickebein" [incl. difference between KG 100 and other LW Kampfverbände], Luftwaffenführungsstab Ia (KM), adressed to "I L", 6 October 1940, g.Kdos, 1 page + 1 map. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) RM 7/2372, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230Q7: "Navigatorische Ausnutzung von Fernfunkfeuern Ukw. (Knickebein)" ["Utilization for navigation of long-range VHF radio beacons (Knickebein)"], memo Az. 47 p 14, B.Nr. 545/40 g.Kdos., signed by Major Schubert for the Chief of Staff of Luftflottenkommando 2, 5 May 1940, 3 pp. [Keywords: Knickebein, coordinates / radio frequency / center beam pointing direction for Stolberg & Kleve, width of the dots & dashes zones, vertical extent of the radiation pattern, 2 pp. utilization guidelines "Merkblatt" - not to be taken into the aircraft; if taken prisoner, no information shall be divulged]. Source: Bundesarchiv (BArch) Freiburg/Germany, file nr. (Signatur) RL 19-6/40 (frmr. RL 19/537), low quality microfiche, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230Q8: "Planung und Erstellung von UKW-Fernfunkfeuern (FFuFd) für die Funknavigation der Luftwaffe" ["Planning for, and construction of, long-range VHF radio navigation beacons of the Luftwaffe"], memo Az. 47 f 68, Nr. 2714/39 g.Kdos., addressed to Reichsminister of Aviation, Supreme Commander of the Luftwaffe, and Chief of the Signal Corps; draft signed by Flight Staff Engineer Gosewisch, 10 September 1939, 12 pp. [Keywords: high priority construction of beacons for Luftwaffe operations over the North Sea; requirements for the first 5 rotable beacons (3x Telefunken G.m.b.H. (high power (3 kW); up to 1200 km range (depending on radio set and aircraft altitude); to be located at Stolberg, Cleve, Borkum; code name Knickebein; antenna system weight ca. 200 metric tons), 2x C. Lorenz A.G. (lower power (500 W); up to 300-600 km range; to be located at Bad St. Peter and on the isle of Sylt; code name Karussel) in terms of equisignal beam width ±0.2° initially (later ±0.1°), dots & dashes zones width ±12°, rotability range ±45° from center beam-direction, radio frequencies compatible with FuBl 1 radio set (29.8-33.6 MHz, 5 fixed frequencies`+ 2 field-modifiable); degree to which the terrain around the beacons must be flat and unobstructed; remote monitoring radio receiver at each site; diagram with dimensions of the Knickebein antenna system and the rotation tracks; table for standard landing beam + Knickebein + Karussel with (humidity dependent) ranges for 3 receiver types (each with 2 different antennas); graph with 0.3° equisignal beam-width and useable altitude vs. range based on beacon signals audibility = vertical usability boundaries of the equisignal beam lobe].  [file size: 25 MB]. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) RL 19-6/40 (frmr. RL 19/537), low quality microfiche, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230Q9: "Geodätische und elektrische Einmessung der Knickebein-Anlage - Richtlinien über die geodätische und elektrische Einmessung der Knickebein-Anlagen - Anforderungen für die Auswahl und Vermessung des Kontrollbogens bei Knickebein-Anlagen" ["Geodetic and electrical calibration of the Knickebein stations - Guidelines fo the calibration - Requirements for the selection and measurement of the verification-arc of Knickebein installations"], As. 47 f 57 Nr. 72/41 g.Kdos., draft signed by Flight Staff Engineer Gosewich, 17 January 1941, 9 pp. [Keywords: all measurement points to be marked with concrete marker (graphic), 0.5° spacing between adjacent markers, 1:5000 maps for Knickebein K-2, sample data sheet for measurements of both dots & dashes beams )]. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) RL 19-6/40 (frmr. RL 19/537), low quality microfiche, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230Q10: "Erläuterungsbericht zu dem Vermessungsarbeiten für den U.K.W.B Kleve - Ergänzung zum Eläuterungsberiche" ["Explanatory report regarding the measurement activities for the Kleve VHF beacon + supplement"; measurement points must have visual contact with the beacon, distance from beacon: measurement with a truck, so measurement points must lie on accessible roads; min & max distance from beacon: 0.8 and 2 km (exceptions possible); no check points allowed near power lines; check point spacing 0.5°; check points marked with marker stone, sign, or nothing; check points also to be marked on the outer concrete ring of the beacon; mentions map in ref. 230Q5], signed by Dip.-Ing Schmitt, 7 pp. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) RL 19-6/40 (frmr. RL 19/537), low quality microfiche, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230Q11: "Krigsminne" ["War memory"], p. 21 in "Kommunedelplan - Kulturarv i Klepp 2005-2016" ["Municipal sub-plan - Cultural heritage in Klepp 2005-2016]", 32 pp. Retrieved October 2020. English translation of p. 21 is here.
• Ref. 230Q12: "Battle of Britain 50 år - Tyske navigasjons- systemer og britiske mottiltak" ["Battle of Britain 50 years - German navigation systems and UK countermeasures"], Halfdan Krohn, pp. 6-13 in "Norsk Militært Tidsskrift", Vol. 160, Nr. 12, December 1990. Source: www.nb.no.
• Ref. 230Q13: "Knickebein på Haugabakka, Klepp", Jan-Martin Nøding (LA8AK, SK 2005), on his webpage "Radarstasjoner og spesielt radionavigasjonsutstyr i Rogaland 1940-45" ["Radar stations and especially radio navigation equipment in Rogaland (Stavanger area)"], update of 29 September 2004. Retrieved 15 June 2022. [pdf]
• Ref. 230Q14: "Die Festung Sylt: Geschichte und Entwicklung der Insel Sylt unter militärischem Einfluss 1894 - 1945", Harald Voigt, Nordfriisk Instituut (publ.), 1992, 254 pp.
• Ref. 230Q15: "Leitstrahlanlage - von Maulburg aus lenkten die Nazis Jagdbomber ins Feindesland" ["Guide beam station - From Maulburg, the Nazis guided fighter-bombers to enemy country"], Gerald Nill, in "Badische Zeitung", 18 August 2020. [pdf]
• Ref. 230Q16: photo number MMD 465-5-3 on contact photo sheet 20 "Canadians in Germany - Date: 10 to 14 Feb. '45, Place: In and Around Cleve & Nijmegen, Photographer: Lieut. M.M. Dean" in "North West Europe - Album 87 of 110, 9 Feb. 45 - 1 March 1945", Canadian Army Numerical 46289-47274 (photo number range), Government of Canada, Library and Archives Canada. Retrieved 11-Oct-2021.
• Ref. 230Q17: "Les stations radars de la Gouinerie et du Petit Parc", a web page of the Mairie de Digulleville (townhall), accessed September 2022. [pdf]
• Ref. 230Q18: "A new look at "The Wizard War", Alfred Price, pp. 15-23 in "Royal Aircraft Historical Society Journal", Issue 28 [Proceedings of the Society's "Electronic Warfare" seminar held at RAF Museum Hendon, 10 April 2002], 2003, 158 pp.
• Ref. 230Q19: "La guerre des radars; 1 - Knickebein - Bernhard" [incl. photos Kn-10, Kn-11], Y. Delefosse, C. Delefosse, in "Archéologie Bunker Magazine", No. 6, 1986, pp. 4-9. Source: 16 August 2017 post on loup-mouton.blogspot.com, retrieved 31 July 2020. [In an October-2022 email exchange, Mr. Y. Delefosse, one of the two authors, confirmed to me that the 1940 photo (ECPA collection) of a Small Kn may have been taken at Kn-11, the photo of the concrete support block was taken at Kn-6, the block has a concrete base below ground level that is wider than the block (thickness & width of that base unknown), the steel I-beam track is 18 cm wide.]
• Ref. 230Q20: Second World War Canadian Army Air Photo Collection, Laurier Military History Archive (LMHA), Laurier Centre for the study of Canada, Wilfried Laurier University, Box 0261 - 2 of 2 "Germany/The Netherlands; North Rhine-Westphalia/Gelderland: Reichswald, Nijmegen, Kleve", Squadron 4, sortie nr. 1614, sortie date: 14 Jan 1945, page 2, negative nr. 4032.
• Ref. 230Q21: Letter from the Stadtarchiv Kleve [City Archive of Kleve], 12 December 2003, content posted in geschichtsspuren.de forum entries on 21 November and 12 December 2003 by EricZ     [pdf]
• Ref. 230Q22: Project'44 - Canadian Overseas Survey and Mapping 1939-1945, W.E. Storey Collection, Sheet 4202-2; the full-size map is here.
• Ref. 230Q23: "Station de radio-guidage codée "K11" (Emetteur Knickebein puis See-Elefant en 1944), Saint-Fiacre (Lanmeur)", source: patrimoine.region-bretagne.fr, retrieved September 2022. [pdf]
• Ref. 230Q24: "Knickebein Transmitter, Noto", Technical Report, Advanced Headquarters Northwest African Air Forces (NAAF), Capture Intelligence Section, A-2, August 1943. The Report cover page is here.
• Ref. 230Q25: "Parcours découverte - Le Mont Pinçon pendant la Seconde Guerre Mondiale" ["A walking discovery tour - Mont Pinçon during WW2"], brochure of the Tourist office of the Pays de Vire / Collines de Normandie, August 2020, 8 pp.  [pdf]
• Ref. 230Q26: "Knickebein - France, Boulogne sur Mer, inland, Haut Pichot". Source: bunkersite.com, accessed 20 October 2022. [pdf]
• Ref. 230Q27: ""Knickebein" Homing-Antenna Device", Wilhelm Runge, United States Army Air Forces (AAF), Air Materiel Command (AMC), Air Documents Division (T-2), Report F-TS-2603-RE (Translation 2603), March 1947, 27 pp. [Knickebein is a directional antenna used for navigational purrposes, operating in a frequency range of from 30 to 33.3 megacycles. The antenna array has a large number of dipoles in a row in order to obtain horizontal beaming and a sharply defined beacon. In addition, vertical beaming is provided to increase the range. Each of the two antenna parts is fed alternately in the rhythm of the signals E-T (dot-dash). A deviation of two and one-half degrees from the beacon axis results only in an amplitude change from seven to seven and one-half scale deviation. Under normal aircraft noise conditions 6.5% is the lowest threshold for safe reception of signals. Further experimentation proved that faster switching from one signal to the other facilitated the identification. The device consists of two stators and one rotor which has no slip contacts. The difference in capacitance, necessary for switching, is produced by the change of the positions of the rotor. Both connection points are stationary, one to the small and the other to the large stator.]
• Ref. 230Q28: "Der Deutsche Rundfunk bis zum Inkrafttreten des Kopenhagener Wellenplans" [transcript only; "German broadcast radio, up to the entry into force of the Copenhagen Frequency Plan" (a.k.a. The "Copenhagen Plan", annex to the 1948 "European Broadcasting Convention"], Gerhart Goebel, in "Archiv für das Post- und Fernmeldewesen", Vol. 2, Nr. 6, August 1950, pp. 355-454. [pdf; sorry: pp. 355-363 only!]
• Ref. 230Q29: "Das Fernsehen in Deutschland bis zum Jahre 1945" ["Television in Germany up to 1945], Gerhart Goebel, in "Archiv für das Post- und Fernmeldewesen", Vol. 5, Nr. 5, May 1953, pp. 259-393. [pdf].  [file size: 26 MB].
• Ref. 230Q30: "Rundfunksender auf Rädern: die fahrbaren Rundfunksendeanlagen der Deutschen Reichspost in den Jahren 1932 bis 1945" ["Broadcast transmitters on wheels: the mobile broadcast stations of the German Reichspost in the years 1932 - 1945"], Bernd-Andreas Möller, Vol. 13 of "Schriftenreihe zur Funkgeschichte", Gesellschaft der Freunde der Geschichte des Funkwesens (GFGF; contributor), Verlag Dr. Rüdiger Walz (publ.), 2003, 197 pp., ISBN-13‏: ‎ 978-3936012026 .
• Ref. 230R: British Air Ministry, etc. WW2 documents that cover Knickebein, "X-system", "Windjammer"/"Bernhard", "Elektra", "Sonne", RAF No. 100 Group). I do not have a copy of these documents - if you do (images, pdf), then please contact me.
• Ref. 230R1: "Extracts from interrogation reports on ‘X Gerat’ and ‘Knickebein’", WO 208/3506, War Office, Directorates of Military Operations and Military Intelligence; Ministry of Defence, Defence Intelligence Staff; MI 9 papers, February 1940 - July 1941. Source: nationalarchives.gov.uk (TNA) catalog entries WO Division 208.
• Ref. 230R2: "Extracts from interrogation reports on ‘X Gerat’ and ‘Knickebein’", WO 208/3507, War Office, Directorates of Military Operations and Military Intelligence; Ministry of Defence, Defence Intelligence Staff; MI 9 papers, 1 June 1940 - 30 April 1941. Source: nationalarchives.gov.uk (TNA) catalog entries WO Division 208.
• Ref. 230R3: "No. 100 Group: Review of operations", AIR 14/2343, Royal Air Force, Air Ministry, Bomber Command, November 1943 – May 1945. Source: nationalarchives.gov.uk (TNA) catalog entries AIR 14.
• Ref. 230R4: "No. 100 Group: Enemy Night Defence", AIR 14/3246, Royal Air Force, Air Ministry, Bomber Command, January 1944 – March 1945. Source: nationalarchives.gov.uk (TNA)  catalog entries AIR 14.
• Ref. 230R5: "‘Knickebein’ enemy navigational aid", AIR 14/3583, Air Ministry, Bomber Command, 1 February 1944 - 21 January 1945. Source: nationalarchives.gov.uk (TNA) catalog entries AIR 14.
• Ref. 230R6: "The Crooked leg: report on "Knickebein": Scientific Intelligence Report No. 6", AIR 20/1623, Air Ministry & Ministry of Defence, Air Historical Branch, Assistant Directorate of Intelligence (Science), June 1940. Source: nationalarchives.gov.uk (TNA) catalog entries AIR 20.
• Ref. 230R7: "‘Knickebein’: German transmitter photographed", September 1940, AIR 20/1626, Air Ministry & Ministry of Defence, Air Historical Branch, Assistant Directorate of Intelligence. Source: nationalarchives.gov.uk (TNA) catalog entries IR 20.
• Ref. 230R8: ""X-Gerat" German blind bombing system", January 1941, AIR 20/1627, Source: nationalarchives.gov.uk (TNA) catalog entries AIR 20.
• Ref. 230R9: "German "X-Gerat"", September 1940, AIR 20/1669, Air Ministry & Ministry of Defence, Air Historical Branch, Assistant Directorate of Intelligence. Source: nationalarchives.gov.uk (TNA) catalog entries AIR 20.
• Ref. 230R10: "German "X-Gerat"", September 1940, AIR 20/1670, Air Ministry & Ministry of Defence, Air Historical Branch, Assistant Directorate of Intelligence. Source: nationalarchives.gov.uk (TNA) catalog entries AIR 20.
• Ref. 230R11: "German "X-Gerat"", October 1940, AIR 20/1671, Air Ministry & Ministry of Defence, Air Historical Branch, Assistant Directorate of Intelligence. Source: nationalarchives.gov.uk (TNA) catalog entries AIR 20.
• Ref. 230R12: "German night fighter radio aids", June 1941, AIR 20/1674 Air Ministry & Ministry of Defence, Air Historical Branch, Assistant Directorate of Intelligence. Source: nationalarchives.gov.uk (TNA) catalog entries AIR 20.
• Ref. 230R13: "Elektra-Sonne": report", July 1945, AIR 20/1705 Air Ministry & Ministry of Defence, Air Historical Branch, Assistant Directorate of Intelligence. Source: nationalarchives.gov.uk (TNA) catalog entries AIR 20
• Ref. 230R14: "List of Benito dayfighter stations" [Y-System], January-December 1943, AIR 40/3006, Air Ministry, Directorate of Intelligence, Air Scientific Intelligence. Source: nationalarchives.gov.uk (TNA) catalog entries AIR 40
• Ref. 230R15: "Report No. 6: ‘The Crooked Leg’. Knickebein (German directional radio beacon)", AIR 40/3046, 1940, Air Ministry, Directorate of Intelligence, Air Scientific Intelligence. Source: nationalarchives.gov.uk (TNA) catalog entries AIR 40.
• Ref. 230R16: "Report No 10: X-Gerat (German system of blind bombing)", January-December 1940, AIR 40/3049, Air Ministry, Directorate of Intelligence, Air Scientific Intelligence. Source: nationalarchives.gov.uk (TNA) catalog entries AIR 40.
• Ref. 230R17: "Report no 12: German beam policy (history of German beam bombing methods)", AIR 40/3051, January-December 1941, Air Ministry, Directorate of Intelligence, Air Scientific Intelligence. Source: nationalarchives.gov.uk (TNA) catalog entries AIR 40.
• Ref. 230R18: "Royal Air Force No. 80 Wing Historical Report, 1940–1945", AIR 41/46, 1946, Air Ministry & Ministry of Defence, Air Historical Branch, Narratives & Monographs, Source: nationalarchives.gov.uk catalog entries AIR 41.
• Ref. 230R19: "With analysis of Navigational Beams (Knickebein) usage", HW 5/5, Government Code & Cypher School, German Section, reports of German Army & Air Force high grade machine decrypts, 12 September 1940 - 10 October 1940. Source: nationalarchives.gov.uk (TNA) catalog entries HW 5.
• Ref. 230R20: "London; 1. NOBILITY reports German use of KNICKEBEIN system to bomb Filton; 2. Intelligence from the Friends", HW 15/43/93, Government Code & Cypher School, Government Communications Headquarters, GRU (Soviet Intelligence), 16 October 1940. Source: nationalarchives.gov.uk catalog entries HW 15.
• Ref. 230R21: "Beams/Radar" [Knickebein, Cherbourg], NCUACS 95.8.00/B.11, 4 August 1940, 1 page, Cambridge University, papers & correspondence of R.V. Jones  Source: nationalarchives.gov.uk (TNA) catalog entries NCUACS 95 Beams/Radar. [not held at Kew Nat'l Archives].
• Ref. 230S: articles and other documentation about "Komet" ("Comet") and "Hermes/Hermine"
• Ref. 230S1: "Tysk Retningsantenneanlæge i Kølby Vest for Nibe" ["German Directional Antenna Installation in Kølby, west of Nibe"; rotating-beam system "Komet"], Commission for the Inspection of German Radio Stations Constructed in Denmark, report by Capt. Bahnsen and Prof. Jørgen Rybner of site visit on 11 Dec 1945, 3 pp. Courtesy M. Svejgaard, used with permission. English translation by me is here.
• Ref. 230S2: "Dora und Komet", secret telegram from the Gen. Nachrichtenführer (Director General of the Signal Corps) to Luftnachrichten Inspektion 5 Abt. III; instructions to halt construction and dismantle installations per instructions Nr. 35513/44 (secret) of same date, staff & guards to be redeployed, Komet at Kölby to remain at disposal of industry for further test/eval, no dismantlement yet of Komet stations - pending special instructions upon test results; dated 27 July 1944. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) RL 2-V/6, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016". Also posted in the geschichtsspuren.de forum (accessed 25 July 2020).
• Ref. 230S3: "Locations of Funksendezentrale (FuSZ) stations with an associated Hermes beacon". This is a kmz file ( = zipped/compressed "Keyhole Markup Language" kml file with annotated map locations) that can be viewed in Google Earth. Easiest to view (i.e., without installing an app): download the file, open Google Earth with Chrome browser (!!!), click on “menu” (3-line "hamburger" icon at top left of window), click on “projects” icon → “open” → “Import KML file from computer” → select the downloaded kmz file and watch!
• Ref. 230T: articles & documents about British & German countermeasures
• Ref. 230T1: "Organisation for Radio Countermeasures", Chapter 7 in "SIGNALS - Volume I: Organisation and Development" [file size: 15 MB], RAF, Air Publication 3237, Air Ministry, Air Historical Branch (A.H.B.), 1958, 125 pp. [Keywords Signals Branch/Group, Signals Flying Units, No. 80 Wing, No. 100 Group, Radio Countermeasures (R.C.M.) and Jamming Committees]. Source: RAF Air Historical Branch Narratives. [pdf]
• Ref. 230T2: "Radio Counter-measures" [file size: 50 MB], Air Publication No. S.D. 686, Vol. VII of "The Second World War 1939-1945 Royal Air Force: Signals", Air Ministry, Air Historical Branch (A.H.B.), 1950, 404 pp. [Keywords: No. 80 Wing, No. 100 Group, KG100, Deviator, Fighter & Bomber Command, U-boats, A.S.V. radar, wireless jamming, Knickebein, Headache, Aspirin, Bromide, Starfish, spoof & rotate, X-Gerät, Ruffian, Y-Gerät, Domino, Benito, Benjamin, Elektra, Wotan, Starfish, E.Bl.3, Windjammer, Cigarette, Sonne, Consol, See-saw, Egon, Briar, Neptun, Meerschaum, Meacon, V1, V2, Moonshine, Tinsel, Shiver, Window, Mandrel, Carpet, Freya, Jostle, Splasher, Corona, Cigar, Ottokar, Rayon, Torch, Dartboard, Boozer, Lichtenstein, Grocer, SN2, Piperack, IFF, Serrate, Freya-Halbe, Naxos, Monica, Flensburg, Dragoon, Overlord]. An easily searchable Table of Contents (text file) is here.  Source: RAF Air Historical Branch Narratives. [pdf]
• Ref. 230T3: "The Air Defence of Great Britain - Volume III: Night Air Defence, June 1940 - December 1941". [Keywords: WWI, early detection/inland tracking/height finding, German blind bombing & navigational aids, gunnery, search lights, sound locators, Ground Controlled Interception (GCI), Air Interception (AI), No. 80 Wing]. Source: RAF Air Historical Branch Narratives. [pdf]
• Ref. 230T4: "German reactions to Allied radio countermeasures: translations of two German documents", January-December 1944, AIR 40/3016, Source: nationalarchives.gov.uk (TNA) catalog entries AIR 40.
• Also see ref. 6B, ref. 230U1, and ref. 230E1.
• Ref. 230U: "Graphic survey of radio and radar equipment used by the Army Air Force", U.S. Army Air Forces, Air Technical Service Command
• Ref. 230U1: Section one, "Countermeasures equipment", 1 February 1945, 89 pp.
• Ref. 230U2: Section three, "Radio navigation equipment", 1 May 1945, 68 pp. [file size: 21 MB]
• Ref. 230U3: Section four, "Radar navigation equipment", 1 July 1945, 138 pp.
• Ref. 230V: "Navigational Aids" [MF & HF D/F, SBA, Radio Ranges, Gee, SCR 277, B/T, BABS, GCA], pp. 24-28 in "The signals war: A brief history of no. 26 Group", AIR 14/3562, UK Air Ministry, Bomber Command, December 1945.
• Ref. 230W: "Aerial Navigation and Traffic Control with Navaglobe, Navar, Navaglide, and Navascreen", H. Busignies, Paul R. Adams, Robert I. Colin, in "Electrical Communication - A Journal of Progress in the Telephone, Telegraph and Radio Art", published by "International Standard Electric Corp.", Vol. 23, No. 2, June 1946, pp. 113-143. Source: worldradiohistory.com, retrieved 17 August 2020.
• Ref. 230Y: "Radionavigation in the UK in World War II", F.C. Richardson, in "The Journal of Navigation", Vol. 45, Issue 1, January 1992, pp. 60-69. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 230Z: "The origins and development of operational resaerch in the Royal Air Force" [incl. I.F.F., Intro of Gee, Intro of Oboe, blind bombing instruments, development of H2S, development of Gee-H], Air Ministry, Air Publication 3368, 1963, 241 pp. Source: raf.mod.uk. Retrieved 20 june 2022.
• Ref. 234: general articles about aviation in Germany through WW2
• Ref. 234A: "Die Flugsicherung in Deutschland vor 1945 - Ein Rückblick" ["Air traffic control and air navigation in Germany before 1945 - a review"], Vol. 1 of "Entwicklung der Flugsicherung in Deutschland" ["Development of air traffic control in Germany"], Frank W. Fischer, International Advisory Group Air Navigation Services (ANSA, self publ.), 2014, 464 pp. [key words incl. blind landing with infrared light, accoustic signal, and the Lorenz system]
• pp. 252, 253, 256-258, 260, 261 from "Funknavigationssysteme" ["Radio navigation systems"], Appendix F (pp. 252-263) to Chapter 4 "Die Entwicklung in den 1920'er, 1930'er und 1940'er Jahren"
• Ref. 234B: "German Commercial Air Transport until 1945", Liudger Dienel, Martin Schiefelbusch, in "Revue belge de philologie et d'histoire – Belgisch Tijdschrift voor Filologie en Geschiedenis", vol. 78, nr. 3-4, 2000, pp. 945-967. [pdf]
• Ref. 235: "blind" landing systems, instrument landing systems, Ground Controlled Approach (GCA)
• Ref. 235A: "Schlechtwetterlandeanlagen" ["Bad-weather landing systems"], Telefunken commercial brochure W.B.160D (2000), 1936 (?), 4 pp. Source: www.cdvandt.org.
• Ref. 235B: installations at various airports
• Ref. 235B1: "20 Jahre Funkstation Dübendorf 1919–1939" ["20 years airport radio station of Dübendorf/Switzerland"], Max Unterfinger, Josef Baumgartner, unpublished typescript, 1939, 472 pp. The referenced photos were published in "Ein Beitrag zur Flugsicherungs Geschichte" ["A contribution about air traffic control history"; ZZ, RDF, Lorenz SBA, FuG-100 & AN/APN-1 radalt, PAR, ILS], Hans H. Jucker, July 2014, 61 pp. Source: www.wrd.ch. Retrieved 18 May 2020.
• Ref. 235B2: pp. 40, 43, 45, 48, 54 in "Gatwick: The Evolution of an Airport" [file size: 21 MB], John King, Issue No. 16 of "Sussex Industrial History - Journal of the Sussex Industrial Archeology Society", 1986, 74 pp. Source: docplayer.net, accessed 24 September 2020.
• Ref. 235B3: pp. 43-45 in "Croydon - Britain's Liverpool of the Air", chapter 2, pp. 29-45 in "European skyways; the story of a tour of Europe by airplane", Lowell Thomas, Boston Houghton Mifflin Co. (publ.), 1927, 524 pp. Source: hathitrust.org, retrieved 9 October 2020.
• Ref. 235B4: in "Engineering, an illustrated weekly journal", 25 December 1936, p. 703.
• Ref. 235B5: "Grande Bretagne" ["Great Britain"] in "Les aviation étrangers" ["Foreign aircraft"] column in "Les Ailes", Vol. 16, No. 780, 28 May 1936, p. 8. Source: Bibliothèque nationale de France, accessed 20 January 2022.
• Ref. 235C: articles of the Institute of Radio Engineers (IRE) -  "Proceedings of the IRE" and "IRE Transactions on Aeronautical and Navigational Electronics" (ANE). Source "Proc. of the IRE": worldradiohistory.com, retrieved June 2014 - May 2020.
• Ref. 235C1: "Report on Experiments with Electric Waves of about 3 Meters: Their Propagation and Use", Abraham Esau, Walter M. Hahnemann, in "Proc. of the I.R.E.", Vol. 18, Issue 3, March 1930, pp. 471-489. [Abstract].
• Ref. 235C2: "A new field application for ultra-short waves", Ernst Kramar, in "Proc. of the IRE", Vol. 21, Nr. 11, November 1933, pp. 1591-1531.
• Ref. 235C3: "The present state in the art of blind landing of airplanes using ultra-short waves in Europe" [1934/35, 33 MHz LOC, 38 MHz markers], Ernst Kramar, in "Proc. of the I.R.E.", Vol. 23, Nr. 10, October 1935, pp. 1171-1182. [Abstract]
• Ref. 235C4: "A Radio Beacon and Receiving System for Blind Landing of Aircraft", H. Diamond, F.W. Dunmore, in "Proc. of the I.R.E.", Vol. 19, Nr. 14, April 1931, pp. 585-626. [Abstract]. NOTE: this is an expanded version of ref. 235Y4 below.
• Ref. 235C5: "A new system for blind landing of aircraft" [VHF (345 MHz) CW transmitter horizontal dipole antenna in aircraft, directional receiving system on ground (2 crossing loop antennas with "equi" direction aligned with runway center line). Long-wave (350 kHz) AM transmitter on ground transmits Localizer deviation (modulation depth) to aircraft], K. Baumann, A. Ettinger, in "Proc. of the I.R.E.", Vol. 24, Nr. 5, May 1936, pp. 751-754.
• Ref. 235C6: "Coupled Networks in Radio-Frequency Circuits" [transmission-line bridge with coupled TL-section, as used in AAC LOC system], Andrew Alford, in "Proc. of the I.R.E.", Vol. 29, Nr. 2, February 1941, pp. 55-70.
• Ref. 235C7: "Instrument Landing at the National Bureau of Standards", Frank G. Kears, in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp. 61-67 [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C8: "Operational Flight Testing of Early Instrument Landing Systems", E.A. Cutrell, in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp. 67-70 [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C9: "Ground-Controlled Approach---Its Development and Early Operational Use", Chester Porterfield, in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp. 71-75, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C10: "All-Weather Landing", J.L. Anast, in "IRE Trans. on ANE", Vol. 1, Issue 2, June 1959, pp. 75-77, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C11: "A Survey of Instrument Approach Systems in the United States", Henry L. Metz, in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp. 78-84, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C12: "Improvements on the Instrument Landing System", in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp.85-94, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C13: "Electronic Landing Aids for Carrier Aircraft", A. Brodzinsky, in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp. 95-99, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C14: "Glide-Slope Antenna Arrays for Use under Adverse Siting Conditions", in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp. 100-111. [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C15: "The FAA Philosophy and Program of Instrument Approach and Landing System Development", L.C. Wright, D.J. Sheftel, in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp. 112-117. [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C16: "A Look at the Future of Automatic Landing Systems", G.B. Litchford, A. Tatz, F.H. Battle, in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp. 118-128, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C17: "An Automatic Landing System", F.D. Powell, in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp. 135-142. [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C18: "The AN/MSN-3: An Automatic Ground-Controlled Approach System", H. Goldstein, B. Cutler, in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp. 142-148, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C19: "Beam transmission of ultra short waves", Hidetsugu Yagi, in "Proc. of the I.R.E.", Vol. 16, No. 6, June 1928, pp. 715-741.
• Ref. 235C20: "The development of a new Station Location or Z-Marker antenna system", J.C. Hromada, in "Proc. of the IRE", Vol. 32, Nr. 8, August 1944, pp. 454-463.
• Ref. 235D: pp. 114-115 in "Sangamo in Peace and War", Part 2 of "Sangamo, a history of fifty years", Robert Carr Lanphier, Benjamin Platt Thomas, 1949, 145 pp. Source: hathitrust.org, accessed 10 September 2020.
• Ref. 235E: "Operation and Maintenance of Lorenz Equipment" and "Ultra-Short-Wave Blind-Approach System", pp. 55-64 and pp. 114-128 in "Aeroplane Radio Equipment - Dealing with Marconi, Standard, and North American radio equipment, with special notes on direction finding equipment, Lorenz equipment, and bonding and screening", Edward Molloy (ed.), Ernest Walter Knott (ed.), Vol. 17 of "Aeroplane Maintenance and Operation Series", Chemical Publishing Company, Inc. (publ.), 1941, 133 pp. Source: hathitrust.org. Retrieved 22 May 2020.
• Ref. 235F: "Schaltung und Aufbau der Sender" ["Circuit and construction of the transmitters"], Part II of "Die Sender und Sendeanlagen der Reichsflugsicherung" ["Circuits & construction of ground-station transmitters"], Vol. 3 of "Flugsicherungstechnische Lehrbücher" ["Air traffic control textbooks"], Hans-Joachim Zetzmann, Georg Siemens Verlagsbuchhandlung (publ.), 1938, 106 pp.
• Ref. 235G: "Die Ultrakurzwelle-Funkbake" ["The VHF radio beacon"; general description and method of operation of an A/N approach guide-beam beacon], E. Kramar, in "Elektrische Nachrichten-Technik (E.N.T.)", Vol. 9, Nr. 12, December 1932, pp. 469-473. Source: cdvandt.org.
• Ref. 235H: articles in "Air Corps News Letter" (source: Air Force Historical Support Division), "Air Force", and "Air Force Magazine" (source: airforcemag.com):
• Ref. 235H1: "First solo blind flight a success" [Hegenberger, localizer + marker beacon], Joseph S Edgerton, in "Air Corps News Letter", Vol. XVI, No. 6, 28 May 1932, pp. 4-5, retrieved 6 September 2020.
• Ref. 235H2: "Collier Trophy presented to Captain Hegenberger", in "Air Corps News Letter", Vol. XVIII, No. 14, 1 August 1935, pp. 4-5.
• Ref. 235H3: "Flying Blind" [Doolittle 1929 flight], C.V. Glines, in "Air Force Magazine", September 1989, pp. 140-141, retrieved August 2020.
• Ref. 235H4: "Shooting landings by radio", F.L. Moseley, in "Air Force: the official journal of the U. S. Army Air Forces", Vol. 27, No. 10, October 1944, pp. 41-44.
• Ref. 235J: articles by Eric M. Conway
• Ref. 235J1: "Blind Landings - Low-Visibility Operations in American Aviation 1918-1958" [general history, why runways?, curved & straight glide path guidance, leader-cable system, SCS-51], Erik M. Conway, The Johns Hopkins University Press (publ.), 2006, 235 pp. Retrieved 2 February 2020 [pdf]
• Ref. 235J2: "The Politics of Blind Landing", Erik M. Conway, in "Technology and Culture", Vol. 42, No. 1, January 2001, pp. 81-106. Source: jstor.com, accessed 23 August 2020. [pdf]
• Ref. 235K: "Blind flying on the beam, aeronautical communication, navigation and surveillance: its origins and the politics of technology". Source: NASA Technical Reports Server (NTRS), retrieved 13 January 2020.
• Ref. 235K1: "Part one: Form and Function", Randy Johnson, in "Journal of Air Transportation", Vol. 8, No. 1, 2003, pp. 37-68
• Ref. 235K2: "Part II: "Political Oversight and Promotion", Randy Johnson, in "Journal of Air Transportation", Vol. 8, No. 2, 2003, pp. 57-78
• Ref. 235K3: "Part III: Emerging Technologies, The Radio Range - The Radio Beacon and Visual Indicator", Randy Johnson, in "Journal of Air Transportation", Vol. 8, No. 2, 2003, pp. 79-104
• Ref. 235L: articles in "Journal of the IEE, Part IIIA: Radiocommunication"
• Ref. 235L1: "The development of c.w. radio navigation aids, with particular reference to long-range operation”, R. V. Whelpton, P. G. Redgment, in Vol. 94, Issue: 11, March-April 1947, pp. 244-254. [Abstract]
• Ref. 235L2: "C.W. Radio Aids to Homing and Blind Approach of Naval Aircraft", D. Quinn, R.D. Holland, in "J. of the IEE, Part IIIA: Radiocommunication", in Vol. 94, Issue 16, March-April 1947, pp. 953-960.
• Ref. 235L3: "C.W. Radio Aids to Approach and Landing", M. Birchall, in Vol. 94, Issue 16, March-April 1947, pp. 943-952
• Ref. 235L4: "Discussion on "C.W. Navigational Aids" at the Radiocommunication Convention, 2^nd April 1947", in Vol. 94, Issue 16, March-April 1947, pp. 1022-1028.
• Ref. 235L5: "Discussion on "C.W. Navigational Aids" - The Author's Replies to the Above Discussion", in Vol. 94, Issue 16, March-April 1947, pp. 1029-1030.
• Ref. 235M: articles about approach and landing procedures (ZZ (QGX), Controlled Descent through Cloud (CDTC), Jägerlandeverfahren, Hegenberger, ...)
• Ref. 235M1: "Um die Sicherheit des Luftverkehrs - Nebel, Vereisung, Schlechtwetter und ihre Überwindung" [incl. ZZ-Verfahren], Kurt W. Streit, in "Prisma : illustrierte Monatsschrift für Natur, Forschung und Technik", Vol. 5, nr. 12, April 1951, pp. 539-545. Source: e-peridodica.ch, retrieved 4 May 2021.
• Ref. 235N: "The Search for an Instrument Landing System, 1918-1948", William M. Leary, Chapter 3, pp. 80-99 in "Innovation and the Development of Flight", Roger D. Launius (ed.), Texas A&M University Press (publ.), 1^st ed., 1999, 335 pp. [pdf]
• Ref. 235P: articles in (popular) radio and aviation magazines, primarily 1930s
• Ref. 235P1: "Flying the Radio Beam", Henry W. Roberts, in "Short Wave Craft", February 1936, pp. 582, 583, 624, 625. Source: worldradiohistory.com, retrieved 28 February 2020.
• Ref. 235P2: "The "Air-Track" System of "Blind Landing"", Charles E. Planck, in "Radio-Craft", Vol. IX, Nr. 4, April 1937, pp. 202, 248, 255. Source: worldradiohistory.com, retrieved 1-July-2020.
• Ref. 235P3: "The Lorenz Blind Landing System", Roderick Denman, in "The Wireless World - The Practical Radio Journal", Vol. XXXVI, Nr. 14, Nr. 814, 5 April 1935, pp. 332-335. Source: worldradiohistory.com. Accessed 21 July 2020.
• Ref. 235P4: "Landing aircraft by sound - a demonstration of the Lorenz Blind Landing System" [Lorenz installation at Heston airport, demo flight with British Continental Airways airplane], in "The Wireless World - The Practical Radio Journal", Vol. XXXVIII, Nr. 26, Nr. 878, 26 June 1936, p. 627. Source: worldradiohistory.com. Accessed 21 July 2020.
• Ref. 235P5: "Radio Aloft", John B. Brennan, in "Radio News", Vol. XIV, Nr. 3, September 1932, pp. 140-141. Source: worldradiohistory.com, accessed 22 July 2020.
• Ref. 235P6: "Air traffic control", in "Wonders of World Aviation", Vol. 1, Part 7, 19 April 1938. Source: wondersofworldaviation.com, accessed 18 August 2020.
• Ref. 235P7: "Down the beam - an amateur tries Heston's Blind Approach System : Technique which requires only practice", H.A. Taylor, pp. 648-649 in "Flight" ["Flight International" since 1962], 18 June 1936.
• Ref. 235P8: "Instrument Landing System for Aircraft - Part I", Henry W. Roberts, in "Aero Digest including Aviation Engineering", Vol. 29, Nr. 10, October 1936, pp. 43-46. Source: library.upenn.edu, retrieved May/July 2020.
• Ref. 235P9: "Instrument Landing System for Aircraft - Part II" [Lorenz blind landing system, burried cable systems (Loth, Simon)], Henry W. Roberts, in "Aero Digest including Aviation Engineering", Vol. 29, Nr, 11, November 1936, pp. 32-36. Source: library.upenn.edu, retrieved May/July 2020.
• Ref. 235P10: "The W.I.T. "Air-Track" System of Instrument Landing" [W.I.T. = Washington Institute of Technology], Henry W. Roberts, "Aero Digest including Aviation Engineering", Vol. 30, Nr. 4, April 1937, pp. 60, 64. Source: library.upenn.edu, retrieved May/July 2020.
• Ref. 235P11: "Lorenz B-L System" [B-L = Blind Landing], in "Aero Digest including Aviation Engineering", Vol. 30, Nr. 6, June 1937, p. 66. Source: library.upenn.edu, retrieved May/July 2020.
• Ref. 235P12: "Lorenz Blind Approach Receivers", advertising by Smith's Aircraft Instruments Ltd., in "Flight", November 1936.
• Ref. 235P13: "Lorenz Blind Approach Receivers", advertising by Smith's Aircraft Instruments Ltd., in "The Aeroplane", 13 January 1937.
• Ref. 235P14: "On the Beam: an explanation of "Standard" Beam Approach - a radio aid for landing aircraft in conditions of poor visibility" (Part 1 & 2) [SBA, Lorenz MCW system, T.U. 3 main LOC beacon, M.U. 3 marker beacons, receiver set, RAF], Frank Preston, in "Practical Wireless", Vol. 22, No. 474, December 1945, pp. 4-9 and Vol. 22, No. 475, January 1946, pp. 50-51. Source: worldradiohistory.com. Accessed 25 August 2020.
• Ref. 235P15: "Radio Landing Systems" [MIT GCA, Lorenz, Lorenz/ITT SBA, SCS-51], P.R. Darrington, in "Wireless World", April 1978, pp. 38-43, 56. Source: worldradiohistory.com, retrieved 20 August 2020.
• Ref. 235P16: "Radio method of blind landing" [Hegenberger, US Army Air Corps, localizer + marker beacon, sonic altimeter], in "Popular Aviation", Vol. 14, No. 3, March 1934, pp. 155-156, 192-193.
• Ref. 235P17: "Weston Aircraft Instruments", Blind Approach Indicator advertising by Sangamo Weston Ltd, 1945-1946.
• Ref. 235P18: "Lorenz Blind Approach Receivers", advertising by Smith's Aircraft Instruments Ltd, as distributor of Standard Radio equipment, 1937.
• Ref. 235P19: "The Problems of Blind Landing", H. C. Pritchard, in "Journal of the Royal Aeronautical Society", Issue 432, Vol. 50, Nr. 12, December 1946, pp. 935-958, with "Discussion" on pp. 958-973. Source: en.booksc.org, retrieved 12 June 201. [Summary]
• Ref. 235P20: "Link Trainer: The infamous "blue box" - history's most prolific flight simulator", pp. 70-71 in "Aeroplane", Issue No. 567, Vol. 48, No. 7, July 2020, pp. 70-71.
• Ref. 235P21: "Fluglandetechnik" [instrument landing], Karl Durst, pp. 102-107 in "Radio-Rundschau - Technisch-wirtschaftliche Zeitschrift", Vol. 1, Nr. 6, September 1946. Source: archive.org, retrieved 15 May 2020.
• Ref. 235P22: "Radiolandingsbakens, Part I - XVI" ["Radio landing beacons", in Dutch language, file size: 21 MB], in "Radio Bulletin", Vol. 18, No. 7-12 (July 1949, pp. 221-224, 246; August 1949, pp. 267-270; September 1949, pp. 304-307, 309; October 1949, pp. 339-342, 355; November 1949, pp. 380-384, 398; December 1949, pp. 440-443, 453), Vol. 19, No. 1-8, 10, 11 (January 1950, pp. 26-29; February 1950, pp. 66-68; March 1950, pp. 105-108; April 1950, pp. 135-137; May 1950, pp. 183-187; June 1950, pp. 209-211, 229; July 1950, pp. 245-248; August 1950, pp. 279-281; October 1950, pp. 351-354, 365; November 1950, pp. 339-402). Source: nvhrbiblio.nl, retrieved 30 September 2020.
• Ref. 235P23: "Latest Type AAF Blind Landing Equipment" [ITT Federal, Indianapolis system, LOC AN/MRN-1, MC-528, GS pattern], M.E. Montgomery, in "Electronic Industries", January 1945, pp. 100-103, 190, 192, 194, 196, 198. Source: worldradiohistory.com, retrieved 4 October 2020.
• Ref. 235P24: "New UHF landing system at Laguardia", in "Electronic Industries", January 1943, pp. 62-64, 107, 108.
• Ref. 235P25: "Happy Landings in Fog", Julian Legget, in "Popular Mechanics", Vol. 59, No. 6, June 1933, pp. 973-975.
• Ref. 235P26: "Lorenz-ultra-korte golf-landingsbaken voor vliegtuigen" ["Lorenz VHF landing beacon for airplanes", in Dutch], H. Veenstra, in "Radio-Nieuws", Vol. 18, No. 3, 15 May 1935, pp. 49-61. Source: nvhrbiblio.nl, retrieved 14 October 2020.
• Ref. 235P27: "IL at ID - The latest demonstration of instrument landing (IL) equipment, the Lorenz system at Indianapolis (ID)", Donald G. Fink, in "Aviation", July 1937, pp. 20, 21, 72, 75. Source: archive.org, retrieved 14 October 2020.
• Ref. 235P28: "La T.S.F." [Télégraphie sans Fil, i.e., "radio" application to aviation; incl. Lorenz landing beacon & associated cockpit instrument], L. Portier, in "Potentiel Aérien Mondial", special 1936 issue for the 15^th "Salon de l'Aéronautique à Paris" of "L'Aérophile", pp. 63-69. Source: Bibliothèque nationale de France (BnF); public domain.
• Ref. 235P29: "Landing on a radio beam", Greg Grant, in "Electronics World + Wireless World", February 1991, pp. 121-124. Source: worldradiohistory.com, retrieved 19 October 2020.
• Ref. 235P30: "The CAA Instrument Landing System - Part I & II", Peter Caporale, in "Electronics", Vol. 18, February 1945, pp. 116-124, March 1945, pp. 128-135. Source: worldradiohistory.com, retrieved 25 October 2020.
• Ref. 235P31: "Landing of aircraft in fog by radio - installation at Newark Airport", H. Diamond, in "Electronics", Vol. 4, No. 6, June 1933, pp.158-161. Source: worldradiohistory.com, retrieved 25 October 2020.
• Ref. 235P32: "40-cm waves for aviation" [MIT 700 MHz localizer beam system], in "Electronics", Vol. 9, No. 11, November 1939, pp. 12-15. Source: worldradiohistory.com, retrieved 25 October 2020.
• Ref. 235P33: "Cathode-Ray Tube used as aircraft instrument indicator" [first integrated CRT-based electronic display: ILS LO/GS deviations or altimeter, artificial horizon, directional gyro, airspeed indicator], in "Electronics", Vol. 10, Nr. 3, March 1940, pp. 36-38. Source: worldradiohistory.com, retrieved 25 October 2020.
• Ref. 235P34: "All-weather flying" [CAA landing system, Omni Ranges, DME, radar, automatic landing], in "Electronics", Vol. 16, Nr. 9, September 1946, pp. 84-87. Source: worldradiohistory.com, retrieved 25 October 2020.
• Ref. 235P35: "Air navigation by wireless - The work of the radio beacons" [Mitchel Field/NY, leader cable, capacity altimeter], in "Wireless World", No. 522, Vol. XXV, No. 9, 28 August 1929, pp. 196-198. Source: nvhrbiblio.nl, retrieved 14 January 2021.
• Ref. 235P36: "Ground-Controlled Approach for aircraft" [GCA], C. W. Watson, in "Electronics", Vol. 15, Nr. 11, November 1945, pp. 112-115. Source: worldradiohistory.com, retrieved 25 October 2020.
• Ref. 235P37: "GCA for Control of Commercial Aviation" [post-WW2 civil version by Gilfillan Bros. Co. of military GCA], in "Electronics", Vol. 16, Nr. 5, May 1946, pp. 160-161. Source: worldradiohistory.com, retrieved 25 October 2020.
• Ref. 235P38: "Status of VHF facilities for aviation" [VHF communication, VHF Range (Localizer), ILS glide-path, VOR], in "Electronics", Vol. 17, Nr. 10, November 1947, pp. 90-95. Source: worldradiohistory.com, retrieved 25 October 2020.
• Ref. 235P39: "Air navigation: survey of radio aids to civil navigation", M.G. Scroggie, in "Wireless World", Vol. 52, No. 11, November 1946, pp. 352-356. Source: worldradiohistory.com, retrieved 3 January 2021.
• Ref. 235P40: "Aerial navigation - radio aids to sky pilotage" [DF, B-T, goniometer, TFK Compass, neon lights, leader cable], Douglas G. Jeffrey, in "Aeronautics" [predecessor of "Popular Aviation" and "Flying Magazine"], Vol. 5, Nr. 6, December 1929, pp. 39-40, 66, 68, 70.
• Ref. 235P41: "The Present State of Development of Radio Instrument Airplane Landing Systems in this Country and Abroad", E. N. Wendell, in "Proceedings of the Radio Club of America", Vol. 15, Nr. 3, March 1938, pp. 22-29. Source: worldradiohistory.com, retrieved 1 April 2021.
• Ref. 235P42: color photo entitled "Experiments in developing instrument landing systems at the CAA Experimental Station, Indianapolis, Indiana. Equipment shown is used for the localizer and glide path", p. 86 of "Color Photography", in "Radio News", Vol. 29, No. 6, June 1943, pp. 82-97. Source: worldradiohistory.com, retrieved 1 April 2021.
• Ref. 235P43: "Instrument Approach System", Peter Caporale, in "Radio News", Vol. 29, No. 6, June 1943, pp. 121-125, 194, 197, 198. Source: worldradiohistory.com, retrieved 1 April 2021.
• Ref. 235P44: "Blind Flying" " [incl. Lorenz beacon, Hegenberger], in "Wonders of World Aviation", Part 15, 14 June 1938, pp. 401-406. Source: wondersofworldaviation.coma, accessed 29 May 2021.
• Ref. 235P45: "Marconi aerodrome approach beacon equipment, type WBD.4" [medium wave, main equi-signal beacon + 2 marker beacons, E/T keying], in "The Marconi Review", No. 66, May-August 1937, pp. 15-22. Source: worldradiohistory.com, retrieved 1 April 2021.
• Ref. 235P46: "Radar and Radar Approach Aids" [GCA], pp. 28-34 in "The signals war: A brief history of no. 26 Group", AIR 14/3562, UK Air Ministry, Bomber Command, December 1945.
• Ref. 235P47: "Blind landing" [Lorenz-IT&T demo at Indianapolis], in "Electronics", July 1937, pp. 26-27. Source: worldradiohistory.com, retrieved 12 June 2021.
• Ref. 235P48: "L'atterrissage sans visibiltié" ["Landing without visibility"], Lt. Vuillot, in "Revue du Ministère de l'air : organe de l'armée de l'air et de ses réserves", Vol. 1, no. 6, 15 June 1935, pp. 743-759. [ZZ-method, concentric leader cables, BoS System by Diamond & Dunmore with cross-pointer instrument, Lorenz E/T system 9 m wavelengh with cross-pointer instrument - end of ZZ]. Source: Bibliothèque nationale de France (BnF), accessed 20 January 2022.
• Ref. 235P49: "Le pilotage sans visibilité exterieure" ["Flying without outside visibility", pp. 354-358 in "Toute l'aviation", Edmond Blanc, 4^th ed., 1931, 494 pp. [Keywords: Rougerie simulator, Z / ZZ method origin, Lorenz method]. Source: Bibliothèque nationale de France (BnF), accessed 20 January 2022.
• Ref. 235Q: "C. Lorenz Aktiengesellschaft, Berlin-Tempelhof", pp. 172-182 in "Reichsverband der deutschen Luftfahrt-Industrie auf der Luftfahrt-Ausstellung, Stockholm, 1936" [catalog by the German aviation industry/trade association of German companies and their products exhibited at the International Aerospace Exhibition at Stockholm/Sweden, May/June 1936; ILIS 1936], 232 pp. Source: justus.ownit.nu, retrieved 31 May 2020. Catalog cover page and table of contents is here, courtesy B. Justusson.
• Ref. 235R: articles about  ILS developments at the CAA, MIT, and WIT
• Ref. 235R1: "The development of the Civil Aeronautics Authority Instrument Landing System at Indianapolis", W. E. Jackson, A. Alford, P.F. Byrne, H.B. Fischer in "Electrical Engineering", Vol. 59, Nr. 12, December 1940, pp. 849-858, and p. 1120 (discussion), [Abstract].  Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235R2: "The CAA-MIT Microwave Instrument Landing System", E.L. Bowles, W.L. Barrow, W.M. Hall, F.D. Lewis, D.E. Kerr, in "Transactions of the American Institute of Electrical Engineers" (IAEE), Vol. 59, Issue 12, 1940, pp. 859-865. Source: booksc.org. [pdf, See note 1]
• Ref. 235R3: "The history and development of the Washington Institute of Technology" [Air-Track, ILS, College Park], Joseph M. Marzolf, 18 November 1938, 23. Source: archive.org, retrieved 3 July 2020. [Summary & introduction].
• Ref. 235S: to be allocated
• Ref. 235T: "The RAE contribution to all-weather landing" [SCS-51, approach lighting, ILS, BLEU], John Charnley, in "Journal of Aeronautical History", Vol. 1, Paper No. 2011/1, 21 pp; Accessed 18 July 2020. [pdf]
• Ref. 235U: reports of the Daniel Guggenheim Fund for the Promotion of Aeronautics
• Ref. 235U1: "The Full-Flight Laboratory", Chapter VII, pp. 29-32 in "The second report of the Daniel Guggenheim Fund for the Promotion of Aeronautics - 1928", January 1929, 48 pp. Source: hathitrust.org, retrieved 25 February 2021.
• Ref. 235U2: "Solving the problem of fog flying; a record of the activities of the fund's full flight laboratory to date", Daniel Guggenheim Fund for the Promotion of Aeronautics, 1929, 52 pp. Source: hathitrust.org, retrieved 21 February 2021.
• Ref. 235U3: "Equipment used in experiments to solve the problem of fog flying - A record of the instruments and experience of the Fund's Full flight Laboratory" [Doolittle's first instrument flight, aircraft equipment], The Daniel Guggenheim Fund for the Promotion of Aeronautics, Inc., March 1930, 57 pp. Source: hathitrust.org, retrieved 18 July 2020.
• Ref. 235V: articles/documents about the RAF military version of the Lorenz landing beam system
• Ref. 235V1: "Standard Beam Approach Ground Installations (F.G.R.I.5069 and T.G.R.I.5041)" [Fixed Ground Radio Installation 5069, Transportable Ground Radio Installation 5041, Transmitter types T.1122, T.1123, T.5041, T.1245], Chapter 4 in "Ground Station Equipment", Section 1 of "Radio Aids to Navigation", Part IV of "Royal Air Force Signal Manual", in Vol. I of "Air Publication 1168" (A.P. 1186, revised ed., June 1940, and AP 1186B, December 1942 / June 1943). Courtesy J. Harris, 2020.
• Ref. 235V2: "Automatic Keying device, Type 2", Chapter 6 in "Ground Station Equipment", in same Section 1 as in ref. 235V1 above, 8 pp. Courtesy J. Harris, 2020.
• Ref. 235V3: "Blind Approach Receivers, R.1124A and R.1125A" [file size: 38 MB], Chapter 7 in "Receivers", Section 3 in "Radio Aids to Navigation", in Part IV of "Royal Air Force Signal Manual" in Vol. I of "Air Publication 1168" (AP 1186), revised ed., June 1940, 55 pp. Courtesy J. Harris, 2020.
• Ref. 235V4: "Blind Approach Receivers, R.1124A and R.1125A", Chapter 7 in "Air Publication 1186", Volume II, Part IV, Section 3 "Receivers", Air Ministry, Royal Air Force Signal Manual, Dcember 1938. Source: tube.radio.com (scanned by Dave Prince VK4KD). Retrieved: November 2022. [file size: 20 MB]
• Ref. 235V5: "Blind Approach Transmitters, T.1122 & T.1123", Chapter 9 in "Air Publication 1186", Volume I, Part IV, Section 1 "Transmitters", Air Ministry, Royal Air Force Signal Manual, December 1938. Source: tube.radio.com (scanned by Dave Prince VK4KD). Retrieved: November 2022. [file size: 28 MB]
• Ref. 235V6: "Beam Approach Aircraft Equipment", chapter 18 of "Standard Notes for Wireless Mechanics", "Air Publication 1938" (A.P. 1938), Air Ministry, reprint of May 1944, 10 pp. Source: blunham.com, retrieved September 2020.
• Ref. 235V7: "Blind Approach Pilot's Handbook" [incl. Lorenz approach/landing beam system; RAF Blind Landing Development Unit at Boscombe Down], Air Publication 1751, Air Ministry, November 1939, ??? pp. An excerpt (6 text pages, 10 figure pages) is here. If you have the complete document, please contact me!
• Ref. 235V8: "The RAE contribution to all-weather landing" [SCS-51, approach lighting, ILS, BLEU], John Charnley, in "Journal of Aeronautical History", Vol. 1, Paper No. 2011/1, 21 pp; Accessed 18 July 2020. [pdf]
• Ref. 235V9: "Approach and landing aids" [Ground Controlled Approach CCA, Airfield Control Radar ACR, Rebecca, Beam Approach Beacon System, BABS, Standard Beam Approach SBA, Rebecca-Eureka, Gee let-down, equipment, procedures, diagrams], pages from an unidentifed WW2 RAF instruction document, 9 pp. Source: part 1 & part 2 - International Bomber Command Centre (IBBC) Digital Archive, University of Lincoln, available under Creative Commons Attribution-NonCommercial 4.0 license. Accessed 1 November 2022.
• Ref. 235W: articles/documents about the USAAF military version of the Lorenz landing beam system (USAAF SCS-51)
• Ref. 235W1: "Army Air Forces' Portable Instrument Landing System", Sidney Pickles, in "Electrical Communication - A Journal of Progress in the Telephone, Telegraph and Radio Art" [broadband "Alford" loop omni-antennas], published by "International Standard Electric Corp", Vol. 22, No. 4, 1945, pp. 262-294. Source: worldradiohistory.com, accessed 17 August 2020.
• Ref. 235W2: "Instrument Flying: Army Air Forces Instrument Approach System", U.S. Army Air Forces, Technical Order No. 30-100F-1, 10 November 1943, 16 pp. Source: aafcollection.info, accessed 1 September 2020.
• Ref. 235W3: "First-Hand: Development of the Instrument Landing System Glide Path" [SCS-51, CAA, Signal Corps, ITT Federal Laboratories, ITT Standard Telephone and Cable, Standard Elektrik Lorenz, 330 MHz, hyperbolic path, straight path, constant rate of descent], Leon Himmel. Source: etwh.org, retrieved 25 June 2020.
• Ref. 235W4: "Air service: radio range and SCS 51 equipment", Exchange of notes between the US Ambassador to the UK and the UK Minister of Civil Aviation, London May 8 and July 31, 1946, regarding transfer of certain WW2 air navigational and operational facilities in the UK, to the UK government. pp. 795-799 in "Treaties and Other International Agreements of the USA, 1766-1949", Vol. 12 "United Kingdom - Zanzibar". Source: US Library of Congress, retrieved 20 October 2020.
• Ref. 235W5: "Synthesis of multifunctional tactical landing system" [incl. SCS-51], G.B. Litchford, Air Force Flight Dynamics Laboratory, Air Force Systems Command, Wright-Patterson Air Force Base, Technical Report AFFDL-TR-67-188, January 1968, 201 pp. Source: dtic-mil, retrieved 29 November 2020.
• Ref. 235X: articles in "Electrical Communication - A Journal of Progress in the Telephone, Telegraph and Radio Art", published by "International Standard Electric Corp". Source: worldradiohistory.com, accessed 17 August 2020.
• Ref. 235X1: "Ultra-Short Wave Radio Landing Beam - The C. Lorenz A.G. Radio Beacon Guide Beam System", R. Elsner, E. Kramar, in Vol. 15, No. 3, January 1937, pp. 195-206.
• Ref. 235X2: "Aviation Radio" section (pp. 218-220) in "Electrical Communication in 1938", in Vol. 17, No. 3, January 1939, pp. 205-229. [Busignies' HF-DF model R.C.5; LMT transportable Adcock; NDB network in Europe, most major airports in Europe now equipped with Lorenz-system VHF ILS; similar development in USA; Australia using similar AN beacons for point-to-point navigation; Lorenz ILS type marker beacons now used along routes in US; 1936/37 experiments with by LMT resulted in improved Lorenz-localizer track and demonstrated in Feb 1938 in France and selected by AF; Western Electric Co. radio altimeter (FM, UHF)]
• Ref. 235X3: "Ultra-High Frequency Loop Antennae", A. Alford, A.G. Kandoian, in Vol. 18, No. 4, April 1940, pp. 255-265.
• Ref. 235X4: "Development of the C.A.A. Instrument Landing System at Indianapolis", Vol. 18, No. 4, April 1940, pp. 285-302.
• Ref. 235X5: "Aviation" [ITT receives order from CAA for "Indianapolis System" ILS at 6 major US cities, to be come operational mid-1941], p. 5 in "Electrical Communication in 1940", Vol. 19, No. 3, 1941, pp. 3-10.
• Ref. 235X6: "Instrument Landing System" and "Ultra High Frequency Two Course Radio Range with Sector Identification", p. 80  in "Western Hemisphere I. T. & T. System Communication: Contributions of 1942", in Vol. 21, No. 2, 1943, pp. 75-84.
• Ref. 235X7: "1938 - First installation of instrument landing equipment at three major London Airports", p. 217 in "Standard Telephones and Cables, Limited, London - 60^th Anniversary", C.W. Eve, in Vol. 21, Nr. 4, 1944, pp. 213-217.
• Ref. 235X8: "Development of Aircraft Instrument Landing Systems", H. H. Buttner, A. G. Kandoian, in Vol. 22, No. 3, 1945, pp. 179-192
• Ref. 235X9: "1937 - Awarded contract for supply of radio instrument landing equipment for the Defence Department, Australian Commonwealth", p. 324 in "Standard Telephones & Cables Pty. Ltd., Australia - 50th Anniversary", J. Clarke, in Vol. 22, No. 4, 1945, pp. 322-325.
• Ref. 235X10: "Standard Beam Approach" p. 6, 11 in "Electrical Communication: 1940-1945, War Years Review - Part I", in Vol. 23, No. 1, 1946, pp. 3-13.
• Ref. 235X11: "Landing aircraft with ground radar" [AN/MPN-1C, Luis Alvarez, Ground Controlled Approach (GCA), Precision Approach Radar (PAR)], J.S. Engel, in "Electrical Communication - Technical Journal of the International Telephone and Telegraph Corporation and Associate Companies", Vol. 24, No. 1, March 1947, pp. 72-81.
• Ref. 235Y: articles and documents from the US Department of Commerce (DoC, incl. Civil Aeronautics Authority / Administration; CAA), US National Academy of Sciences (NAS), and National Advisory Commission on Aeronautics (NACA)
• Ref. 235Y1: "Diamond-Dunmore", pp. 16-20 in "Federal Science Progress", U.S. Dept. of Commerce, Vol. 1, No. 3, April 1947.
• Ref. 235Y2: "Description and theory of Instrument Landing System", Federal Airways Manual of Operation IV-B-1-4, U.S. Dept. of Commerce, Civil Aeronautics Administration, 1st ed., 15 October 1949, 43 pp.
• Ref. 235Y3: "The CAA Radio Instrument Landing System with Simultaneous Voice", U.S. Department of Commerce, Civil Aeronautics Administration, Office of Federal Airways, Technical Development Services, 1946, 31 pp.
• Ref. 235Y4: "A radio system for blind landing of aircraft in fog", H. Diamond, F.W. Dunmore, in "Proceedings of the National Academy of Sciences [PNAS] of the Unite States of America", Vol. 16, Nr. 11, 15 November 1930, pp. 678-685. [pdf]
• Ref. 235Y5: "History of Instrument Landing System glide paths", Chapter 1 (pp. 1-20) in "An Airport Glide-Path System Using Flush-Mount, Travelling-Wave Runway Antennas, Vol. II", Richard H. McFarland, Ohio State University Research Foundation, Report 891-2, for the FAA Aviation R&D Service (frmr. Bureau of R&D), 31 March 1961, 177 pp. Source: dtic.mil, retrieved 25 October 2020.
• Ref. 235Y6: "The development of a straight-line glide path", J.M. Lee, H.I. Metz, Civil Aeronautics Administration, U.S. Department of Commerce, Technical Development Report No. 55 (TDR55), June 1947, 34 pp. Source: hathitrust.org, retrieved 16 January 2021.
• Ref. 235Y7: "The CAA-RTCA instrument landing system - Part I: Development and installation" [low quality scan], Henry I. Metz, Civil Aeronautics Administration, U.S. Department of Commerce, Technical Development Report No. 35 (TDR 35), October 1943, 83 pp. Source: planeandtrainwrecks.com, retrieved 16 January 2021.
• Ref. 235Y8: "The CAA-RTCA instrument landing system - Part II: Tests and modifications" [low quality scan],, Henry I. Metz, Civil Aeronautics Administration, U.S. Department of Commerce, Technical Development Report No. 36 (TDR 36), October 1943, 29 pp. Source: planeandtrainwrecks.com, retrieved 16 January 2021.
• Ref. 235Y9: "Development of a VHF directional localizer - Part I (preliminary tests) & II (the monitor)", Chester B. Watts, Samuel E. Taggart, Kennard E. Voyles, CAA Technical Development & Evaluation Center, Technical Development Report No. 183 (CAA TDR 183), May 1954, 43 pp. Source: hathitrust.org, retrieved 25 October 2020.
• Ref. 235Y10: "Methods for facilitating the blind landing of airplanes", M. Heinrich Gloeckner, National Advisory Commission on Aeronautics (NACA), Technical Memorandum No. 687 (NACA-TM-687), 1 October 1932, 28 pp. Source: ntrs.nasa.gov, retrieved 19 February 2021. Translated from "Verfahren zur Erleichterung von Blindlandungen", pp. 347-355 in "Zeitschrift für Flugtechnik und Motorluftschiffahrt" (ZFM), Vol. 23, No. 12, 24 June 1932.
• Ref. 235Z: newspaper articles
• Ref. 235Z1: "Landing a 'plane "blind" - How pilots are guided by the Lorenz wireless beam", in "The Manchester Guardian", 22 January 1937, p. 12.
• Ref. 235Z2: "To test new radio beams and landing gear for planes" [blind landing system of Lorenz + Bureau of Air Commerce + Army tested at Indianapolis (no obstacles in area), Lorenz beacon & receivers], in "Moline Daily Dispatch" (Moline/IL/USA), Vol. 59, 24 April 1937, p. 11, 13.
• Ref. 235Z3: "Last word in modern safety devices being tested at Municipal Airport - Engineers expect equipment to eliminate air tragedies - Blind flying systems and "Tricycle" landing gear under severe trials" [blind landing system of Lorenz + Bureau of Air Commerce + Army tested at Indianapolis (no obstacles in area), Lorenz & receivers, E. Donovan], A.F. Casse, in "The Indianapolis Sunday Star", 25 April 1937, p. 71.
• Ref. 235Z4: "Airplanes to push blind flying" [improved Lorenz VHF system, secretly installed at Indianapolis, marker beacons; DoC experimented with it in 1932; compared to Hegenberger system at Oakland/CA], in "Des Moines Tribune", 30 April 1937, p. 10.
• Ref. 235Z5: "U. S. flyers try European "blind" landing system" [Indianapolis, demo by ITT ( = "Lorenz Low Approach" system)], Wayne Thomis, in "Chicago Daily Tribune", Vol. XCVI, No. 116C, 15 May 1937, p. 7.
• Ref. 235Z6: "Croydon airport - Front door to the world" [Lorenz, Plessey, and Marconi landing beam systems recently installed], in "Chicago Sunday Tribune", Vol. XCVII, No. 1, 2 January 1938, p. 100.
• Ref. 235Z7: "Automatic plane landing system is perfected by Army engineers" [test 2 years at Wright Field, Dayton/OH; War Dept. hand off to Bureau of Air Commerce], in "The Indianapolis Star", Vol. 36, No. 36, 11 July 1938, p. 9.
• Ref. 235Z8: "In Manchester - Ringway will defy fog" [Ringway airport, illuminated fog-line + Lorenz beacon, first outside London airports], in "The Manchester Guardian", 8 November 1938, p. 13.
• Ref. 235Z9: "Conquest of foggy landings for airplanes believed near - Novel radio control and tunnel dissipator studied in effort to bring ships safely to ground when ceiling remains at zero" [M.I.T. system, 3 lights on instrument panel, guidance by "radioed lights"; also mentions Bendix, Lorenz, Air-Track systems; chemical fog dissipators/absorbers], in "Arizona Daily Star" (Tucson/AZ), 14 January 1939, p. 5.
• Ref. 235Z10: "In Manchester - Landing by ear" [Lorenz E/T (!) aural landing beam being added], in "The Manchester Guardian", 26 July 1939, p. 11.
• Ref. 235Z11: "Blind landings" [CAA specs, A. Alford, Int'l Telephone Development Co., Bell Telephone Labs, newly selected standard system (75-112 MHz, GS + LOC), MIT "horn" system (UHF, microwave)], in "The Evening Sun" (Baltimore/MD), Vol. 60, 23 January 1940, p. 4.
• Ref. 235Z12: "Private flying in new year - Blind approach systems" [Standard Beam Approach System (Lorenz) shows no improvement over pre-war Lorenz system at Hendon], in "The Manchester Guardian", 28 December 1945, p. 2.
• Ref. 241: "Erprobungsstellen der Luftwaffe" [Luftwaffe test sites, incl. Rechlin, Süd/Foggia, Tarnewitz, Travemünde, Udetfeld, Werneuchen]. Bestandsbeschreibung [file description] of Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL 36/.... Retrieved 28 August 2019.
• Ref. 244: Luftwaffe & Royal Air Force fighter intercept & control methods ("Jagdverfahren"), maps, and related topics
• Ref. 244A: "Nachtjagd" [intro, descriptions, and evaluations], Luftwaffe document, date unknown, 18 pp. Source: German Russian Project for digitization of archives in the Russian Federation. Retrieved 29 August 2019.
• Ref. 244B: "Bestimmungen über Nachtjagd" [descriptions of methods, and instructions to Flak organisation regarding night fighting], 1^st Flakdivision, Berlin, 19 November 1943, 12 pp. Source: German Russian Project for digitization of archives in the Russian Federation. Retrieved 29 August 2019.
• Ref. 244C: "Mosquito Nachtjagd", [specific fighter and flak tactics against incoming British "Mosquito" fighter-bombers] 1^st Flakdivision, Berlin, 7 March 1944, 5 pp. Source: German Russian Project for digitization of archives in the Russian Federation. Retrieved 29 August 2019.
• Ref. 244D: "Das Y-verfahren für Tag- und Nachtjagd" ["The Y-Procedure for day and night fighter control (navigation method)"], document without reference number, author unknown, without date (but before May 1945), without place, 114 pp. The 1960s file coversheet of the Militärgeschichtliches Forschungsamt (Research Office for Military History) suggests that it dates to 1940/41, 114 pp. [file size: 82 MB !!!! - with reduced resolution [file size: 84 MB; good-but-lower-reslution file is here 27 MB],
• Complete description of the "Y" procedure for day & night fighter control from ground plotting stations with short wave equipment. Keywords: Y-Verfahren, Y-Führung, Y-Stelle, Y-Stellung, Y-Anlage, Y-Station, Y-Einrichtung, E 16, FuG 16, Graetz-E-Mess-Gestell, Siemens-E-Mess-Gestell, Heinrich Peiler, ZVG 16, ZE ZY Zeiger, Schildkröte, PQK, S 16.
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) RL 2-V/38, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 244E: "Anlage 1 zu Luftflottenführungsabteilung Ia op2 Nr. 500/41 geh." [file size: 28 MB; good-but-lower-resolution file is here, 4 MB]. Map is not dated.
• Map covers area of Belgium, The Netherlands, Denmark, northern Germany incl. Berlin. Map is marked with locations of militärische Sperrgebiete, Nachtsperrgebiete, Nachtjagdgebiete, Dunkle Nachtjagdsräume.
• Map size: 4x2 (WxH) A4-sheets. Map is low-quality blueprint copy.
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) RL 20/186/K, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 244F: "Einsatzbeispiel für einen Feindeinflug" (example of response to intruding enemy aircraft). Map is not dated. [file size: 84 MB; good-but-lower-resolution file is here, 10 MB].
• Map shows ground track of enemy bomber stream arriving from Britain with target Frankfurt, intercepting fighters, timing, etc. Map includes large & detailed table of the entire nightfighter intercept process, from long-range radar detection to "kill", with step-by-step status/activity/communication at the level of Flugmeldekompanie, Nachtjagdraum, Fühlungshalter, Jagdgruppe, Flugmeldungszentrale, Fluko, and Flak; the entire sequence covers 1 hr 40 min. Map size: 4x5 (WxH) A4-sheets.
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) RL 36/443, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016"
• Ref. 244G: "Luft-Navigationskarte in Merkatorprojektion - Erweitertest Blatt Deutschland mit Jägernetz", Bodenorganisation Großraum-Nachtjagd Luftflotte Reich, July 1944. Source: Bestand/File 500, Findbuch/Index 12452, Akte/record 286 of the German-Russian Project for the Digitization of German Documents in Archives of the Russian Federation. Retrieved 28 August 2019.
• Ref. 244H: "Nederland en de Duitse Nachtjacht - Van jager tot prooi" (The Netherlands and German night fighting - from hunter to prey), W.H. Lutgert, R. de Winter, pp. 536- 545 in "Militaire Spectator", vol. 183, nr. 12, December 1994. Accessed September 2019. [pdf]
• Ref. 244J: "Nederland en de Duitse Nachtjacht - Van jager tot prooi (Deel 2)" (The Netherlands and German night fighting - from hunter to prey - part 2), W.H. Lutgert, R. de Winter, pp. 5-17 in "Militaire Spectator", vol. 184, nr. 1, January 1995. Accessed September 2019. [pdf]
• Ref. 244K: "De Luftwaffe en Nederland - Balans van een oorlogserfenis" (The Luftwaffe and The Netherlands - legacy of a war), W.H. Lutgert, R. de Winter, pp. 450- 459 in "Militaire Spectator", vol. 184, nr. 10, October 1995. Accessed September 2019. [pdf]
• Ref. 244L: "Nachtjagdnavigationskarte - herausgegeben von NJG.3.-NO" [night-fighter navigation chart issued by the Nachrichten-Offizier of the no. 3 night fighter-wing, Nachtjagdgeschwader 3]. [file size: 25 MB]
• Map is not dated. Bernhard-stations Be-0, Be-6, Be-8 through Be-12 are also marked on this map. Source: collection R. Grywatz.
• Ref. 244M: "Tag- und Nachtjagd, 3. Jagddivision (als beispiel)".  Map is dated 29 July 1944.  [file size: 24 MB; good-but-lower-resolution file is here, 9 MB].
• Map covers area of The Netherlands to Heilbronn/Germany. Map is marked with location of Tagjagdstellungen and Fu.M.G. sites (1., 2., and 3. Ordnung; dunajafähig vs. nicht dunajafähig).
• Map size ca 3x2 (WxH) sheets of size A4. Map scale 1:1.000.000
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) RL-3-1527.
• Ref. 244N: "Jagd-Einsatz im November 1943", Anlage 3 (appendix 3) to "Lfl.Kdo3, Führ.Abt(1)/1c No. 15684/43 Kdos". [file size: 19 MB]
• Large bar graph for each day of November 1943, with total number of fighter sorties for each day, split into "day" and "night" fighter. Also: table with statistics for each day: number (with type(s) of aircraft) for each type of sortie/mission: "Alarmstart" / "Überwachung und Sperre" / "Geleitschutz" / "Begleitschutz u. Augnahme"; / "Nachtjagd" (night fighter) / "Fernjagd" (long range intercept); also: total number of sorties/missions, number of enemy kills (incl. type of enemy aircraft), own losses.
• Size: size: ca. 3x3½ (WxH) A4-sheets.
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) RL-3-1527.
• Ref. 244P: "Abschüsse der Nachtjagd im Bereich Luftwaffenbefehlshaber Mitte", Anlage 2 (appendix 2).
• Graph with three lines: "hell" (helle Nachtjagd), "dunkel" (dunkle Nachtjagd), "kombiniert" (kombinierte Nachtjagd). Graph covers monthly statistics regarding enemy kills for the period April 1941 - March 1942.
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) RL-3-1527, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 244Q: "Anzahl der voll u. bedingt (ab Juli 1941) bzw. eingeschränkt (ab Mai 1943) einsatzfähigern Besatzungen" and "Anzahl der einsatzbereiten Kampf-Flugzeuge" .  [file size: 17 MB]
• Graph with monthly statistics for the period mid-1939 - mid-1939: number of available flight crews and number of operational fighter planes), separate curves for "Tagjäger" (day fighters) and "Nachtjäger" (night fighters; from late 1940 onward).
• Also: interesting large table with 53 key dates of the WW2, from 1 September 1939 (German invasion of Poland) through 15 August 1944 (anglo-american landing in southern France).
• Size: ca. 1½ x3 (WxH) A4-sheets.
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) RL-3-1527.
• Ref. 244R: "Fighter defence of Germany - Control of fighters by the "Y" Procedure", Samuel Denys Felkin (Chief Interrogator at Bletchley), transcribed report from the British Air Ministry, Assistant Director of Intelligence (Prisoner Interrogation), A.D.I. (K) Report No. 525/1944, 14 pp. Source: The National Archives of the UK, ref. AIR40/2875 and 2876. Retrieved from www.cdvandt.org.
• Ref. 244S: "Die Deutschen Nachtjagdverfahren" ["The German nigh fighter procedures"], Walter Grabmann, Generalmajor a.D., date unknown, 22 pp.
  [Helle Objektjagd, helle Gebietsjagd, Himmelbett, Verfolgungsnachtjagd [pursuit night], Objektjagd "Leichentuch" / "Milchglas", 1-mot Objektjagd "Wilde Sau", Fernnachtjagd [long-range night], Zusammenarbeit mit Jäger-Flak, 13 maps].
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) ZA 3/402a, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 244T: "Besprechung bei General Galland am 21.1.43" ["Meeting with Gen. Galland on 21 Jan 1943"], signed by Major Eisermann, 22 January 1943, 3 pp. [Keywords: possibility of fighter control from an aircraft carrier ("Flugzeugträger"), limitations of Freya FuMG radar for that application, proposal from Plendl to install Y-RDF system (Y-Boden-Anlage), aircraft carier to have landing beam system for fighters; the Y fighter control system (Y-Verfahren) meets its requirements but has serious practical problems due to frequency changes and exposure of the equipped lead aircraft]
• Bundesarchiv (BArch) Freiburg/Germany, Signatur/file nr. RL 16-3/12, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 244U: WW2 documents of the British Air Ministry, Directorate of Intelligence. I do not have a copy of these documents - if you do (images, pdf), then please contact me.
• Ref. 244U1: "German controlled night fighter system", February 1943, AIR 20/1633, Air Ministry & Ministry of Defence, Air Historical Branch, Assistant Directorate of Intelligence. Source: nationalarchives.gov.uk (TNA) catalog entries AIR 20.
• Ref. 244U2: "German control of fighter aircraft", July 1944, AIR 20/1642, Air Ministry & Ministry of Defence, Air Historical Branch, Assistant Directorate of Intelligence. Source: nationalarchives.gov.uk (TNA) catalog entries AIR 20.
• Ref. 244U3: ""Benito" and "Egon" German control of fighters", April 1945, AIR 20/1650, Air Ministry & Ministry of Defence, Air Historical Branch, Assistant Directorate of Intelligence. Source: nationalarchives.gov.uk (TNA) catalog entries AIR 20.
• Ref. 244U4: "German night fighter control", December 1942, AIR 20/1663, Air Ministry & Ministry of Defence, Air Historical Branch, Assistant Directorate of Intelligence. Source: nationalarchives.gov.uk (TNA) catalog entries AIR 20.
• Ref. 244U5: "Report No 17: controlled nightfighter system", January-December 1943, AIR 40/3060, Air Ministry, Directorate of Intelligence, Air Scientific Intelligence. Source: nationalarchives.gov.uk (TNA) catalog entries AIR 40.
• Ref. 244U6: "Report No 33: Benito and Egon control of fighters", January-December 1945, AIR 40/3067, Air Ministry, Directorate of Intelligence, Air Scientific Intelligence. Source: nationalarchives.gov.uk (TNA) catalog entries AIR 40.
• Ref. 245: papers about Luftwaffe broadcast via radio telephony of enemy aircraft positions.
• Ref. 245A: "Feindreportagen" ["Running commentary on enemy aircraft"] and "Bernhard-Führung" ["Bernhard guidance"], §II and §VII, respectively, in "Nachrichtenbefehl April 1945 (Nachtjagd)", 1. Jaddivision, Nafü 3 - Nr. 2600/45, 18 March 1945, 5 pp.
• Keywords: Verfolgungsnachtjagd, Führungswellen, Gruppenbefehlswellen, Geschwaderbefehlswellen UKW (Tast) Bord-Bord, Divisionsführungswellen Lgw, Kzw, UKW der 1.J.Div., Divisionsklärungswellen (Tast), Y-Linienverteilung für Aufklärer, Y-Linien für 1-mot. Nachtjagd, Mosquito-Jagd (Silber), Feindreportagen, Kennung für Fu. G 25, Rufzeichen und Rufnamen, Optische Gruppenkennung und Wellen für flg. Funkfeuer, Verschlüsselung eigener Standort- und Flughöhenangaben, Gebietsnachtjagd, Flugsicherung.
• Source: Bestand/File 500, Findbuch/Index 12476, Akte/record 90, pages 31-36 of the German-Russian Project for the Digitization of German Documents in Archives of the Russian Federation. Retrieved November 2021.
• Ref. 245B: "Funkübermittlung der feindlichen Luftlage – Auszug aus einem Bericht des Obst. Morgenstern, Chef beim Generalnachrichtenführer vom 22.3.1945" ["Radio transmission of the enemy air situation (aircraft positions) – Excerpt from a report dated 22 March 1945 of Col. Morgenstern, Chief adjoint to the lead Signal Corps General"], Gen.Nafür (1. Abt.) Nr. 11 319/45 geh., 9 pp.
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur)  ZA 3/402, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 245C: "Die Bildung der Luftlage. 1935 – 1944 (Flugmeldedienst, Funkmeßdienst, Funkaufklärung)" ["The creation of (enemy) air situation (aircraft position status). 1935 – 1944 (enemy aircraft warning service, radar service, radio intelligence service)"], Obst. A.D. Greffrath, 1946, 7 pp.
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) ZA 3/402, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 245D: "Die Bildung der Luftlage" ["The creation of (enemy) air situation (aircraft position status)"], Gen.Maj. a.D. Walter Grabmann, no date - possibly 1946, 10 pp.
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany (Signatur) file nr. ZA 3/402, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 247: "Air mail beacon Farmerville, Pa., Lighted by Kohler Electric Plant", cover panel of "Light for the Night Air Mail", 3 page folded sales brochure of "Kohler of Kohler - Automatic Electric Plants" of the Kohler Co. in Kohler, Wisconsin/USA. Date unknown. Source: atchistory.org. Accessed 21 July 2020.
• Ref. 252: "Rhubarb operations: Appendix V - German navigational beam stations. France, Holland and Belgium" [file size: 108 MB], AIR 40/1661, 142 pp., 1942 (with amendments made in 1942 and 1943), Air Ministry, Directorate of Intelligence and related bodies: Intelligence Reports and Papers, Deputy Director of Air Tactics. Document pages are not numbered. Item is in the collection of The National Archives; material with UK Crown Copyright, used in accordance with the Open Government License [pdf].
• Ref. 252A: "Introduction", 10 pp. A "Rhubarb" was a routine tactical operation, in which a small number of RAF aircraft flew at low-level into France or Belgium, to strafe ground targets.This particular document covers German beam stations (Knickebein, Y, X, and "Knickebeins of a new type" = Bernhard) along the Atlantic coast of France and North Sea coast of The Netherlands. Map coordinates are provided for all targets.
• Ref. 252B: "Desvres/Le Bois-Julien (Target V/18)" [ = "Bernhard" Be-3], 4 pp. (including 2 photos and 1 site/area layout map; pp. 108-111 in the complete document). Observations: circular concrete base appr. 100 ft in diameter. Hut at the center of the array. Mast some 50 ft high at 600 yards to northwest of the installation, connected by underground cable. Photos from recce sorties in March and June of 1941.
• Ref. 252C: "Sizun/St Michel (Target V/24)" [ = "Bernhard" Be-2 at Mt.-St.-Michel-de-Brasparts], 3 pp. (including 1 photo and 1 site/area layout map; pp. 134-135 in the complete document). Photo from September 1942 recce sortie. Observations: circular concrete base appr. 100 ft in diameter. Hut at the center of the array. Cable trench of ca. 950 ft in westerly direction, to short mast.
• Ref. 252D: "St. Vaast/La Pennelle (Target V/26)" [ = "Bernhard" Be-4], 4 pp. (including 2 photos and 1 site/area layout map; pp. 139-142 in the complete document). Observations: circular concrete base appr. 100 ft in diameter. Hut at the center of the array. Photos from recce sorties in April and September of 1942. Note: "La Pernelle" is misspelled as "La Pennelle".
• Ref. 252E: "Commana (Target V/1)" [ = "Y" station ?], 4 pp. Recce sortie in July of 1941.
• Ref. 252F: "La Feuillée (Target V/2)" [ = "Y" station Y8 "Friedrich"], 6 pp. Recce sortie in September of 1941.
• Ref. 252G: "Lanmeur (Target V/3)" [ = "Knickebein" station Kn-11], 8 pp. Recce sorties in July 1940, January & September of 1941, July of 1942.
• Ref. 252H: "Laye (Target V/4)" [ = "X" station X-#], 5 pp. Recce sorties in November of 1940 and September of 1941.
• Ref. 252J: "Beaumont-Hague (Target V/5A)" [ = "Knickebein" station K-9], 6 pp. Recce sorties in October of 1940, March & September of 1941.
• Ref. 252K: "Jobourg (Target V/5B)" [ = "Y" station Y7 "Anton"], 9 pp. Recce sorties in October of 1941, March & September of 1941, February, April, and September of 1942.
• Ref. 252L: "Sortosville-en-Baumont (Target V/6)" [ = "Knickebein" station Kn-10], 6 pp. Recce sortie in April of 1942.
• Ref. 252M: "Mt. Pincon (Target V/7)" [ = "Knickebein" station Kn-8], 4 pp. Recce sortie in June of 1941.
• Ref. 252N: "Greny (Target V/8)" [ = "Knickebein" station Kn-7], 5 pp. Recce sorties in June & October of 1941.
• Ref. 252P: "Mt. Violette (Target V/9)" [ = "Knickebein" station Kn-6], 5 pp. Recce sorties in June of 1941.
• Ref. 252Q: "Mt. de la Louve (Target V/10)" [ = "X" station X-#], 8 pp. Recce sorties in May & November of 1941, August & October of 1942
• Ref. 252R: "Cassel/La Croix Rouge (Target V/12)" [ = "Y" station Y2 "Berta"], 7 pp. Recce sorties in February of 1941, April & July of 1942.
• Ref. 252S: "Bergen op Zoom (Target V/13)" [ = "Knickebein" station Kn-5], 5 pp. Recce sorties in September & October of 1941.
• Ref. 252T: "Julianadorp (Target V/14)" [ = "Knickebein" station Kn-3], 4 pp. Recce sortie in March of 1941.
• Ref. 252U: "Bayeux/Le Mesnil (Target V/15)" [ = "Elektra" station 3], 4 pp. Recce sorties in April & June of 1942.
• Ref. 252V: "St. Valery-en Caux/St. Martin-aux-Bunaux  (Target V/16)" [ = "Y" station Y4 "Dora"], 5 pp. Recce sorties in June of 1942.
• Ref. 252W: "St. Valery-en Caux/Conteville de Palleul (Target V/17)" [ = "Y" station Y3 "Cicero"], 5 pp. Recce sorties in October 1940, May & July of 1942.
• Ref. 252X: "Boulogne/Boursin (Target V/19)" [ = "Y" station Y6 "Gustav"], 4 pp. Recce sorties in April & July of 1942.
• Ref. 252Y: "Petten/Groet (Target V/20)" [ = "Elektra" station E-#]   Sonne-5, between Petten and Groet (just north of Groet), Dutch coast., 4 pp. Recce sorties in July of 1941, June of 1942.
• Ref. 252Z: "Baumont / Hague Town (Target V/21)", Y-type beam station, per Fig. in the Introduction.
• Ref. 252AA: "St.-Pierre-Église / Dargougerie (Target V/22)" [ = "Erika" station Er-2], 4 pp. Recce sorties in June of 1940, and April  of 1942.
• Ref. 252AB: "Morlaix/Plougourvest (Target V/25)" [= "Elektra" station 4], 3 pp. Recce sortie in September of 1942.
• Ref. 254: "Richtfunkfeuer und Drehfunkfeuer" [directional and rotating radio beacons], E. Kramar, Berlin, 18 pp., in "Ringbuch der Luftfahrttechnik", Vol. 15, VC3 (V. Ausrüstung, C. Funkpeilung, 3), Berlin-Adlershof, Zentrale f. wiss. Berichtswesen b. d. Deutschen Versuchsanst. f. Luftfahrt, 1938. [file size: 28 MB]
• Ref. 255: "Bestandsbeschreibung Bestandssignatur BArch RL 21 "Fliegerhorstkommandanturen und Flugplatzkommandos der Luftwaffe"". Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, content description of file nr. (Signatur) RL 21. Retrieved 2 November 2019.
• Ref. 259: pp. 75-84 in "Zwischen Möhrenfeld und Panzerkute - verblassende Erinnerungen im märkischen Sand. Die märkischen Dörfer Groß- und Kleinbeuthen und ihre Umgebung in schwerer Zeit um 1945", Bernd Saalfeld, self published book (available via Heimatverein Beuthen e.V.), 2018, 156 pp.
• Ref. 261: German and Allied radar systems used in WW2 European war theatre
• Ref. 261A: "Hülsmeyer and the early days of radar inventions, sense and nonsense, a survey" and "Part II", Arthur O. Bauer, 2004/2005, 74 pp. (Part I) and 18 pp. (Part II). Source: www.cdvandt.org. [pdf Part I] [pdf Part II]
• Ref. 261B: radar-related articles from "IEEE Aerospace and Electronic Systems Magazine" and "Proceedings of the IEEE"
• Ref. 261B1: "IEEE HISTORIC MILESTONE - Christian Hülsmeyer: Invention and First Demonstration of Radar, 1904", Hugh Griffiths, Peter Knott, Wolfgang Koch, in "IEEE AES Magazine", Vol. 34, Issue 9 , September 2019, pp. 56-60. A preliminary version of this article is here, 9 pp. Retrieved 22 January 2020.  [pdf]
• Ref. 261B2: "The long prelude (1873-1922): Phase I of the invention of radar", J.B. McKinney, in "IEEE Aerospace and Electronic Systems Magazine", Vol. AES-21, Iss. 8, September 2006, pp. 17-25. Source: en.booksc.org, accessed April 2021. [pdf, See note 1].
• Ref. 261B3: "The rise of radio (1922-1930): Phase II of the invention of radar", J.B. McKinney, in "IEEE Aerospace and Electronic Systems Magazine", Vol. AES-21, Iss. 8, September 2006, pp. 27-39. Source: en.booksc.org, accessed April 2021. [pdf, See note 1].
• Ref. 261B4: "The arrival of radar (1930-1935): Phase III of the invention of radar", J.B. McKinney, in "IEEE Aerospace and Electronic Systems Magazine", Vol. AES-21, Iss. 8, September 2006, pp. 41-54. Source: en.booksc.org, accessed April 2021. [pdf, See note 1].
• Ref. 261B5: "The race with destiny (1935-1939): Phase IV of the invention of radar", J.B. McKinney, in "IEEE Aerospace and Electronic Systems Magazine", Vol. AES-21, Iss. 8, September 2006, pp. 55-73. Source: en.booksc.org, accessed April 2021. [pdf, See note 1].
• Ref. 261B6: "Radar becomes operational (1939-1941): Phase V of the invention of radar", in "IEEE Aerospace and Electronic Systems Magazine", Vol. AES-21, Iss. 8, September 2006, pp. 75-78. Source: en.booksc.org, accessed April 2021. [pdf, See note 1].
• Ref. 261B7: "GCA radars: Their history and state of development", H.R. Ward, C.A. Fowler, H.I. Lipson, in "Proceedings of the IEEE, Vol. 62, Issue 6, June 1974, pp. 705-716. Source: en.booksc.org, accessed 24 May 2021. [pdf, See note 1].
• Ref. 261C: "Some Aspects of German Airborne Radar Technology, 1942 to 1945", Arthur O. Bauer, 2 December 2006, 32 pp. Source: www.cdvandt.org, retrieved May 2019.
• Ref. 261D: "CH - The First operational Radar" [Chain-Home], pp. 73-83 in "GEC Journal of Research - Incorporating the Marconi Review", Vol. 3, No. 2, 1985. Retrieved 27 January 2020. [pdf]
• Ref. 261E: "Bomber's Radar - General Survey of the Three Primary Systems Used by Bomber Command", C.B. Baily-Watson, pp. 252-254 in "Flight", 6 September 1945.
• Ref. 261F: "Einsatz "Berlin"-Gerät" [Operation of "Berlin"-device = German version of the British "H2S" ground-mapping radar].
• Letter from Gen.Nafü (1.Abt.), addressed to gen.Nafü/Ln.Insp. (6.Abt.). Letter ref. Nr. 12493/44 geh. (1.Abt.II). Letter is dated 17 Juli 1944. Letter states that after referral with Generals Martini & Peltz, the IX.Fl.Korps will, until further notice, not use the "Berlin"-Gerät", as 1) current test/evaluation status is not yet sufficient for operational service, and 2) this navigation aid is not needed in the "Landekopfraum" [Allied landing/invasion area = Normandy]. The "Berlin"-Gerät" is not allowed to be used without permission from Lw.Fü.Stab.
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) RL 2-V/5, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 261G: Untitled letter/telegram about "Lichtenstein SN 2" and "Lichtenstein B/C"
• Letter/telegram from OKL Fü.Stab/Gen.Nafü. (Rob.), addressed to Luftfl.Kdo.1,4, 6. and Lw.Kdo. Südost. Letter ref. Nr. 10910/44. Letter is from 1944 (exact date not marked). Letter states that loss [to the enemy] of night fighter radar search equipment "Lichtenstein SN 2" must absolutely be avoided, to make it harder for the enemy to develop interference means. Therefore, night fighters missions with "Lichtenstein SN 2" over enemy territory and bandit territory [ = occupied territories with active resistance groups] is forbidden. Night fighters with missions over bandit territory in the East will only be equipped with "Lichtenstein B/C" until further notice. Note: "(Rob.)" at the end of the "from" part refers to the special trainset "Robinson" at the disposal of  the Gen.Nafü.
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) RL 2-V/5, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 261H: "Deflating British radar myths of World War II", Maj. G.C. Clark, Air Command and Staff College Research Dept., AU/ACSC/0609F/97-3.
• Ref. 261J: books about radar history and technology
• Ref. 261J1: "Radar Origins Worldwide: History of Its Evolution in 13 Nations Through World War II", R.C. Watson, Trafford Publishing, 2009, 420 pp.
• Ref. 261J2 "Die deutschen Funkmeßverfahren bis 1945" ["German radar through 1945"], Fritz Trenkle, Motorbuch Verlag Stuttgart, 1979, 209 pp.
• Ref. 261J3: "Radar Handbook", Merril I. Skolnik (ed. in chief), McGraw-Hill, 2^nd ed., 1990, 846 pp. Source: University of Zürich, Dept. of Geography, accessed 14 July 2020 [file size: 41 MB]. [pdf]
• Ref. 261J4: "Die Radarschlacht, 1939-1945: Die Geschichte des Hochfrequenzkrieges" ["The radar battle, 1939-45 - The history of the HF war"], Werner Niehaus, Motorbuch Verlag (publ.), January 1977, 246 pp.
• Ref. 261J5: "Technical History of the Beginnings of Radar" [basic principles of radar and historical aspects of their evolution; limited to the pre-cavity magnetron era of radar], Sean S. Swords, IET History of Technology Series 6, 342 pp. Source: b-ok.cc, retrieved 22 October 2020 [file size: 22 MB]. [pdf - See note 1].
• Ref. 261J6: "Technical and Military Imperatives - A Radar History of World War II", Louis Brown, Institute of Physics Publishing, 1999, 563 pp. [pdf - See note 1].
• Ref. 261K: documents about the "Würzburg" radar (FuMG39/FuSE62)
• Ref. 261K1: "Geschichte der Funkortung - Funktionsmodell des Funkmessgerätes "Würzburg" FuMG 62 (D)" [History of radar, funtional model of the "Würzburg" radar], Hans-Peter Opitz, pp. 12-16 in "Funkgeschichte - Mitteilungen der Gesellschaft der Freunde der Geschichte des Funkwesens (GFGF)", Vol. 34, Nr. 195, February/March 2011. See note 1
• Ref. 261K2: "Funk-Sende-Empfangsgerät FuSE 62 (Flak-Meßgerät FMG 39 T)", Werkstattbuch part E 01-1, 7 pp. Source: www.cdvandt.org. Retrieved 2 September 2019. [pdf]
• Ref. 261K3: "Das Orten mit Fu.M.G. 39 T bei Feindstörung" [target location with FuMG 39T radar during enemy jamming & chaff/window/reflectors], Merkblatt, 1^st Flakdivision, 6 January 1944, 33 pp.Source: German Russian Project for digitization of archives in the Russian Federation. Retrieved 29 August 2019.
• Ref. 261K4: "Deckname „Würzburg“", Arthur O. Bauer, Verlag Historischer Technikerliteratur (publ.), 1966, 133 pp. Source: www.cdvandt.org. Retrieved 2 September 2019. [pdf]
• Ref. 261K5: "Geschichte der Funkortung - Funktionsmodell des Funkmessgerätes „Würzburg‟ FuMG 62 (D)", Hans-Peter Opitz, pp. 12-16 in "Funkgeschichte - Mitteilungen der Gesellschatf der Freunde der Geschichte des Funkwesens", Vol. 34, Vol. 195, February/March 2011.  See note 1
• Ref. 261L: p. 9 in "The Century of Radar - from Christian Hülsemeyer to Shuttle Radar Topography Mission", Wolfgang Holpp, based on his presentation "The Century of Radar" at the German Radar Symposium, Bonn/Germany, 2002 with 2004 update, 27 pp. [pdf]
• German version: "Das Jahrhundert des Radars - von Christian Hülsemeyer zur Shuttle Radar Topography Mission"  [pdf].
• Ref. 261M: "Deckname „Würzburg“ - Ein Beitrag zur Erhellung der Geschichte des geheimnisumwitterten deutschen Radargeräts 1937-1945" ["The technical history of the Würzburg radar system"], Arthur O. Bauer, Verlag Historischer Technikliteratur (publ.), 103 pp. Source: www.cdvandt.org. Accessed 28 March 2020. [pdf]
• Ref. 261N: "The History of Radar Technology in Germany - Reference to its Application to Radio Location" [Würzburg-A/C/Riese, Freya, Philips, GEMA, Lorenz 39L/40L, Elefant, Mammut, Seeburg, Lichtenstein SN2] , H. Diehl. Special Felkin report.
• Ref. 261P: "The State of German Centimetre Wave Technology at the End of the Second War", L. Brandt, special Felkin report?
• Ref. 261Q: "Eureka-H Radar Beacons in World War II" [VHF DME], F.R. Hunt, 12 pp., Chapter 14 of "Canadians on Radar - Royal Canadian Air Force 1940-1945", George K. Grande, Sheila M. Linden, Horace R. Macaulay, 2003; retrieved 2 May 2020.
• Ref. 261R: "Radar development in Canada" [WW2], Frederick H. Sanders, in "Proceedings of the Institute of Radio Engineers (I.R.E.)", Vol. 35, Nr. 2, February 1947, pp. 195-200. Source: worldradiohistory.com, retrieved 28 June 2020.
• Ref. 261S: "Microwaves detect aircraft" [Telefunken bi-static radar system, 10 cm wavelength / 3 GHz], in "Electronics, Vol. 10, nr. 9, September 1935, pp. 284-285. Source: worldradiohistory.com, retrieved 16 April 2021.
• Ref. 261T: "Air Navigation Systems: Chapter 5. The Development of British Airborne Primary Radar, 1935–1945", Brian Kendal, in "The Journal of Navigation", Vol. 47, Issue 3, September 1994, pp. 277-294. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 261U: articles about Doppler radar
• Ref. 261U1: "History of Doppler Radar Navigation", Walter R. Fried, in "Navigation: Journal of the Institute of Navigation", Vol. 40, Issue 2, Summer 1993, pp. 121-136. [Abstract] . Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 261U2: "A Historical Survey of the Application of the Doppler Principle for Radio Navigation", Ernst Kramar, in "IEEE Trans. on Aerospace and Electronic Systems", Vol. AES-8, Iss. 3, May 1972, pp. 258-263
• Ref. 261V: "The radar war, 1930-1945", Gerhard Hepcke (mediocre translation into English by H. Liebmann), 53 pp. Source: radarworld.org, accessed 5 September 2020. [brief overview/timeline keywords description of: pip-squeak, ILS, hyperbolic, Ingolstadt, Elektra, Sonne, Seetakt ship radar, Freya ground radar, Stichling IFF for Freya, Würzburg ground radar, Erstling IFF for Würzburg, Chain Home (CH) coastal ground radar, Type 79Y ship radar, Anti Surface Vessels (AVS) airborne radar, Air Intercept (AI) radar, Breslau I & II jamming stations, R3000 IFF, Masking Beacons (Meacon), Knickebein, X Procedure, Y Procedure, Postkutsche Procedure, Caruso jamming station, FuMB 1 Gee, Rebecca-Eureka, Heinrich, Metox R600 warning receiver, Olga warning receiver, Lichtenstein night fighter airborne radar, Mannheim FLAK radar, Moonshine, Wasserman groundradar, Karl jamming station, Wespe IFF, Leigh-light procedure, Oboe I Bumerang procedure, Window Chaff Tinsel, Würzlaus, K-Laus, H2S Rotterdam Gerät, Naxos & Naxos-W & Naxburg & Korfu airborne warnign receivers, Roderick jamming transmitter, Tuba ground jamming transmitter, SS Loran, Shoran, Hohentwiel U submarine radar, Oboe navigation procedure, Mandrel, Taxanble, Glimmer, Titanik, GH Discus, Feuerstein, Rotterheim, Berlin A & N1 & N2 airborne radar, Roland & Feuerball, Jagdschloß & Forsthaus ground panorama radar, Pauke gun laying radar] [pdf]
• Ref. 261W: radar articles from Wireless World magazine, source: worldradiohistory.com, retrieved Sept-2020 - Jan-2021
• Ref. 261W1: "Radiolocation - Part 1", R.L. Smith-Rose, in "Wirelesss World", Vol. LI, Nr. 2, February 1945, pp. 34-37, source: worldradiohistory.com, accessed 17 September 2020.
• Ref. 261W2: "Radiolocation - Part 2: History of its development", R.L. Smith-Rose, in "Wirelesss World", Vol. LI, Nr. 3, March 1945, pp. 66-70. Part 1 & 2 were reprinted as "Radar" [RDF, radiolocation, radar], R.L. Smith-Rose, in "Electrical Communication - A Journal of Progress in the Telephone, Telegraph and Radio Art", published by "International Standard Electric Corp.", Vol. 22, No. 3, 1945, pp. 171-178.
• Ref. 261W3: "Achievements of Radar - Its part in the war", in "Wireless World", Vol. 51, No. 9, September 1945, pp. 269-270.
• Ref. 261W4: "Fundamentals of Radar 1. - Ground stations: The development of Pulse Technique" [Chain Home (CH, CHL)], in "Wireless World", Vol. 51, No. 10, October 1945, pp. 299-303.
• Ref. 261W5: "Fundamentals of Radar 2. - Night fighter equipment : relation between power, beam width and range", in "Wireless World", Vol. 51, No. 11, November 1945, pp. 326-329.
• Ref. 261W6: "Fundamentals of Radar 3. - Radar as a weapon of offense : ASV and H2S", in "Wireless World", Vol. 51, No. 12, December 1945, pp. 363-365.
• Ref. 261W7: "Fundamentals of Radar 4. - Pulse methods applied to navigation" [Oboe, Gee], in "Wireless World", Vol. 52, No. 1, January 1946, pp. 23-26.
• Ref. 261W8: "Fundamentals of Radar 5. - Beacons employing pulse technique" [ASV, IFF, H2S, Eureka, BABS], in "Wireless World", Vol. 52, No. 2, February 1946, pp. 55-56.
• Ref. 261X: "A Brief History of the Development of Radar in Great Britain up to 1945", Richard M. Trim, in "Measurement and Control", Vol. 35, December 2002, pp. 299-301. Source: journals.sagepub.com, accessed 18 September 2020
• Ref. 261Y: "Radar for Blind Bombing - Part I & II" [H2X airborne radar], J.V. Holdam, S. McGrath, A.D. Cole, in "Electronics", Vol. 16, Nr. 5, May 1946, pp. 138-143, Vol. 16, Nr. 6, June 1946, pp. 142-149. Source: worldradiohistory.com, retrieved 25 October 2020.
• Ref. 261Z: "Directory of German Radar Equipment" [airborne and ground-based], War Department Technical Manual TM E11-219, April 1945, 74 pp.
• Ref. 261AA: articles about Oboe
• Ref. 261AA1: ""Oboe": How it Works", Air Ministry record AIR 20/1471, July 1943. Available at The National Archives (TNA), Kew/UK; catalog item description - I do not have a copy of this item. Please contact me if you do. Note: the TNA catalog includes 95 "AIR OBOE" records.
• Ref. 261AA2: ""Oboe": history compiled by No. 60 Group HQ", Air Ministry record AIR 16/917, 1940-1945. Available at The National Archives (TNA), Kew/UK; catalog item description - I do not have a copy of this item. Please contact me if you do. Note: the TNA catalog includes 95 "AIR OBOE" records.
• Ref. 261AA3: "Oboe: bomber navigation radar", Ministry of Aviation record AVIA 7/377, 1943-1944. Available at The National Archives (TNA), Kew/UK; catalog item description - I do not have a copy of this item. Please contact me if you do. Note: the TNA catalog includes 98 "AVIA OBOE" records.
• Ref. 261AA4: "Bumerangstörung im Ruhrgebiet" [Jamming of "Bumerang" (German codename for Oboe-guided British Mosquitoes) in the Ruhr area), Nr. 82 514/44 g.Kdos. (3.Abt.III). Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL 2-V/6, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016
• Ref. 261AB: "Technical and Military Imperatives - A Radar History of World War II", Louis Brown, Institute of Physics Publishing, 1999, 579 pp. Source: digi.lib.ttu.ee, accessed October 2022. [pdf]
• Ref. 262: articles about hyperbolic radio navigation systems
• Ref. 262A: "GEE and LORAN - Radar Navigational Systems World War II", W.P. Campbell, 16 pp., Chapter 16 of "Canadians on Radar - Royal Canadian Air Force 1940-1945", George K. Grande, Sheila M. Linden, Horace R. Macaulay, 2003; retrieved 2 May 2020.
• Ref. 262B: "An Introduction to Loran", John Alvin Pierce, in "Proc. of the Institute of Radio Engineers (IRE) and Waves and Electronics", Vol. 34, Nr. 5, May 1946, pp. 216-234 . Source: worldradiohistory.com, retrieved 27 June 2020.
• Also reprinted as "An Introduction to Loran", John Alvin Pierce, in "IEEE Aerospace and Electronic Systems Magazine", Vol. 5, No. 10, October 1990, pp. 16-33. [pdf]
• Ref. 262C: "Robert J. Dippy: The Hyperbolic Radio Navigation System", Robert I. Colin, in "IEEE Trans. on Aerospace and Electronic Systems", July 1966, pp. 476-481.
• Ref. 262D: "GEE and LORAN - Radar Navigational Systems World War II", W.P. Campbell, 16 pp. [pdf]
• Ref. 262E: "1969 IEEE Pioneer Award - William Joseph O'Brien & Harvey Fischer Schwarz" [Award for invention, development, implementation of DECCA], in "IEEE Trans. on Aerospace & Electronic Systems", November 1969, pp. 1013-1020. [pdf]
• Ref. 262F: "LORAN Long Range Navigation", J.A. Pierce, A.A. McKenzie, R.H. Woodward, Vol. 4 of Massachusetts Institute of Technology (MIT) Radiation Laboratory Series, McGraw-Hill Book Co. Inc. (publ.), 1948, 490 pp. [file size: 25 MB].
• Ref. 262G: "LORAN (Long Range Aid to Navigation)", U.S. Dept. of Commerce, Civil Aviation Authorities (CAA), Airways Operations Training Series, Bulletin No. 7, June 1949, 16 pp., source: hathitrust.org, retrieved 6 June 2020.
• Ref. 262H: "The Loran system - Part I, Part II (Loran Receiver-Indicator), Part III (Loran transmitting-station)", in "Electronics", Vol. 15, Nr. 11, November 1945, pp. 94-99, Vol. 15, Nr. 12, December 1945, pp. 110-115, Vol. 16, Nr. 3, March 1946, pp. 109-115.
• Ref. 262J: "Decca Navigator - Continuous-wave navigation system", in "Wireless World", Vol. 52, No. 3, March 1946, pp. 93-95. Source: worldradiohistory.com, accessed 17 September 2020.
• Ref. 262K: "Decca Navigator stations - details of the transmitter chain", M.G. Scroggie, in "Wireless World", Vol. 52, No. 8, August 1946, pp. 260-262. Source: worldradiohistory.com, accessed 17 September 2020.
• Ref. 262L: "Air Navigation Systems Chapter 4. Hyperbolic Airborne Radio Navigation Aids – A Navigator's View of their History and Development", W.F. Blanchard, in "The Journal of Navigation", Vol. 44, Issue 3, September 1991, pp. 285-315. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 262M: "Early history of the Decca Navigator system", Claud Powell, in "Journal of the Institution of Electronic and Radio Engineers", Vol. 55, Issue 6, June 1985, pp. 203-209. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 262N: "The Genesis of the Decca Navigator System", Walter Blanchard, in "Journal of the Institution of Electronic and Radio Engineers", Vol. 68, Issue 2, March 2015, pp. 219-237. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 262P: "Hyperbolic origins", Claud Powell, in "The Journal of Navigation", Vol. 34, nr. 3, September 1981, pp. 424-436.Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 262Q: "Beschreibung des "Erika"-Verfahrens (Suportung)" ["Decription of the "Erika" system"], W. Pfister, Reichsstelle für Hochfrequenzforschung e.V. [RHF; Reich's Agency for High Frequency Research], Ferdinand-Braun-Institut, Berlin/Adlershof, 26 May 1943, 17 pp.
• Bundesarchiv-Militärarchiv (BArch-MA, BAMA) in Freiburg/Germany, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016". BArch/BAMA file nr. (Signatur) RL 39/244.
• Also see ref. 2C6.
• Ref. 263: articles about the C. Lorenz A.G. company
• Ref. 263A: "Das Auge am Marktgeschehen – Die Lorenz-Röhre und der Sieg nach 1945" ["Watching the market - the Lorenz valve and victory after 1945"], Jakob Tschandl, pp. 45-53 in "Fliegen und Funktechnik - Die Flugzeugfabrik der Luftwaffe Berline-Tempelhof 1933-1945" ["Aviation and radio - The Luftwaffe aircraft factory at Berlin-Tempelhof 1933-1945"], Marcus Popplow (ed.), Beate Winzer (ed.), Universitätsverlag der TU Berlin (publ.), 60 pp. Creative Commons License CC BY 4.0. Retrieved 22 May 2020.
• Ref. 263B: "Telephone and telegraph industry: Manufacture of equipment", pp. 42-50 in "American Industry in Europe", Frank Allan Southard, Vol. 6 of "The Evolution of International Business 1800-1945", Houghton Mifflin (publ.) 1931, 264 pp. Source: hathitrust.org. Accessed 22 May 2020.
• Ref. 263C: "ITT: The Management of Opportunity", Robert Sobel, Beard Books (publ.), 2000, 421 pp.
• Ref. 263C1: pp. 72-73 [Lorenz]
• Ref. 263C2: pp. 102-111, 158-161 [ITT, Federal Telephone & Radio Corp., Federal Labs]
• Ref. 263D: "75 Jahre Lorenz, 1880 - 1955. Festschrift der C. Lorenz Aktiengesellschaft Stuttgart" [keywords: Fernschreiber, "Goliath" transmitter, FuG 10, FuG 16, "Schwabenland" receiver, Funkhorchempfänger, Flugzeug Bordfunk, Richtfunk, Röhren, Funkortung], 1955, 272 pp. [file size: 53 MB; with OCR]. Source: archive.org.
• Ref. 263D1: "Lorenz-Beiträge zur Funkortung" ["Lorenz contributions to radio navigation"; Scheller beam, localizer, glideslope keyed equisignal, Elektra, SBA, Australia], Ernst Kramar, pp. 155-162.
• Ref. 263D2: "Meilensteine der Großsendertechnik" ["Milestones of large transmitter technology"; "Goliath", Doherty Weißkirchen, Feldberg], Erich Schulze-Herringen, Erich Heineke, Felix Gerth, pp. 68-80.   [file size: 25 MB].
• Ref. 263E: "100 Years of Wireless Telephony in Germany: Experimental Radio Transmission from Eberswalde and Königs Wusterhausen", Wolfgang Mathis, Anja Titze, in "Advances in Radio Science" (ARS, an open-access journal of the Union Radio-Scientifique Internationale / International Union of Radio Science (U.R.S.I.) Landesausschuss Deutschland e.V., distributed under CCA 4.0 license), Vol. 19, pp. 93-104, Dec 2021.
• Also see ref. 164C ("Report on C. Lorenz A.G.")
• Ref. 265: articles about IFF, interrogator-transponder/responder based systems, Distance Measuring Equipment (DME)
• Ref. 265A: "The Eureka-Rebecca compromises: another look at Special Operations security during World War II", Chris Burton, in "Air Power History", Vol. 52, No. 4, Winter 2005, pp. 24-37. Source: afhistory.org, retrieved 19 June 2020.
• Ref. 265B: articles about Oboe
• Ref. 265B1: ""Oboe": How it Works", Air Ministry record AIR 20/1471, July 1943. Available at The National Archives (TNA), Kew/UK; catalog item description - I do not have a copy of this item. Please contact me if you do. Note: the TNA catalog includes 95 "AIR OBOE" records.
• Ref. 265B2: ""Oboe": history compiled by No. 60 Group HQ", Air Ministry record AIR 16/917, 1940-1945. Available at The National Archives (TNA), Kew/UK; catalog item description - I do not have a copy of this item. Please contact me if you do. Note: the TNA catalog includes 95 "AIR OBOE" records.
• Ref. 265B3: "Oboe: bomber navigation radar", Ministry of Aviation record AVIA 7/377, 1943-1944. Available at The National Archives (TNA), Kew/UK; catalog item description - I do not have a copy of this item. Please contact me if you do. Note: the TNA catalog includes 98 "AVIA OBOE" records.
• Ref. 265B4: "Bumerangstörung im Ruhrgebiet" [Jamming of "Bumerang" (German codename for Oboe-guided British Mosquitoes) in the Ruhr area), Nr. 82 514/44 g.Kdos. (3.Abt.III). Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL 2-V/6, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 265C: "The Traffic Alert and Collision Avoidance System", James K. Kuchar, Ann C. Drumm, in "Lincoln Laboratory Journal", Vol. 1, Nr. 2, June 2007, pp. 277-296.   [pdf]
• Ref. 266: articles about radio course guidance via radiating & magnetic leader cables (C. Stevenson (1893), Owens (1901-1903), F.A. Kolster (1918/19), W.A. Loth, Blancard, E.J. Simon, A.H. Marriott, et al.)
• Ref. 266A: articles about the Loth system
• Ref. 266A1: "Le pilotage par câble électrique, système Loth, des navires et des aéronefs" ["Pilotage of ships and aircraft by means of the "Loth System" electric cable"], P. Letheule, in "Le Génie Civil : revue générale des industries françaises et étrangères", Vol. LXXIX, no. 24, no. 2052, 10 December 1921, pp. 505-510. Source: Bibliothèque nationale de France; public domain.
• Ref. 266A2: "The Loth guide cable - an interesting French aid to air navigation", in "Flight International Magazine", Vol. XIV, No. 11, 16 March 1922, pp. 163-164. Source: archive.org, retrieved 21 July 2020.
• Ref. 266A3: "The Loth guide cable for flying in fog. French invention for guiding aircraft through fog described. System functions in preliminary trial." in "Aviation" (predecessor of "Aviation Week"), Vol. 12, No. 15, 10 April 1922, pp. 422-423. Source: hathitrust.org, accessed 21 July 2020.
• Ref. 266A4: "The 'Loth leader cable system' for electrical steering of aeroplanes", John. S. Gray, in "Minutes of Proceedings of the Institution of Aeronautical Engineers", Nr. 9, 1923, pp. 7-30.
• Ref. 266A5: "Guidage magnétique des aéronefs et aérodromes de securité" ["The Magnetic Guidance of Aircraft; Safety Aerodromes"], William Loth, in "Comptes rendus hebdomadaires des séances de l'académie des sciences" ["Weekly minutes of the sessions of the academy of sciences"], Vol. 189 (July-December 1929), 14 October 1929, pp. 572-573. Source: Bibliothèque nationale de France; public domain. [Summary]
• Ref. 266A6: "The Loth navigation system: a twin rotating beacon method of emitting wireless signals that can be picked up on an ordinary receiver", R.J. de Marolles, in "Aircraft Engineering and Aerospace Technology", Vol. 2 No. 5, 1 May 1930, pp. 107-108. Source: en.booksc.org, retrieved 12 June 2021.
• Ref. 266A7: "Guidage Loth" ["Loth guidance"], pp. 349-351 in "Toute l'aviation", Edmond Blanc, 4^th ed., 1931, 494 pp. Source: Bibliothèque de France (BNF) on-line library, accessed 20 January 2022.
• Ref. 266D: NACA/NASA Reports & Memos. Source: NASA Technical Reports Server (NTRS).
• Ref. 266D1: "On the problem of guiding aircraft in a fog or by night when there is no visibility", William Loth, National Advisory Committee for Aeronautics (NACA), Technical Memo 57 (NACA-TM-57), January 1932, 5 pp. (translated from "Comptes redues des séances de l'académie des sciences", nr. 23, 5 December 1921). Source: NTRS, retrieved 21 July 2020. [Abstract]
• Ref. 266D2: "Automated landing, rollout, and turnoff using MLS and magnetic cable sensors", S. Pines, S.F. Schmidt, F.I. Mann, NASA Contractor Report 2907 (NASA-CR-2907), 1 October 1977, 152 pp. Source: NTRS, retrieved 21 July 2020.
• Ref. 266D4: "Results from tests, with van-mounted sensor, of magnetic leader cable for aircraft guidance during roll-out and turnoff" [B-737], James C. Young, W. Thomas Bundick, Stewart H. irwin, NASA Technical Paper 2092, January 1983. 40 pp. Source: NTRS, retrieved 24 August 2020.
• Ref. 266D4: "Results of aircraft open-loop tests of an experimental magnetic leader cable system for guidance during roll-out and turn-off", W. Thomas Bundick, David B. Middleton, NASA Technical Memorandum 4135 (NASA-TM-4135), NASA, Scientific & Technical Information Div., 1990, 39 pp. Source: NTRS, retrieved 21 July 2020.
• Ref. 266D5: "Effects of cable geometry and aircraft attitude of a magnetic leader cable system for aircraft guidance during rollout and turnoff", W. Thomas Bundick, NASA Technical Paper 1978, April 1982, 31 pp.
• Ref. 266D6: "Results of aircraft open-loop tests of an experimental magnetic leader cable system for guidance during roll-out and turn-off", W. Thomas Bundick, David B. Middleton, NASA Technical Memorandum 4135, NASA, Scientific & Technical Information Div., 1990, 39 pp. Source: NASA Technical Reports Server, retrieved 21 July 2020.
• Ref. 266E: newspaper articles
• Ref. 266E1: "Guiding aircraft in fogs - French to test new cable device" [Loth cable along top of telepgraph poles, planned 18 km section out of Le Bourget], in "The Manchester Guardian", 4 January 1923, p. 7.
• Ref. 266E2: "Air landing in fog" [buried Loth leader cable in circle around Le Bourget, left/above/right + relative strength for height; several years experimented at Farnborough], in "The Manchester Guardian", 1 August 1928, p. 8.
• Ref. 266E3: "Letters to the editor - The first wireless message" [Charles A. Stevenson claims invention of leader cable], in "The Observer", Vol. 147, No. 7677, 17 July 1938, p. 8.
• Ref. 266F: articles in "L'Aérotechnique", "L'Aérophile", "L'Aéro", and "Les Ailes" magazines - 1921-1935
• Ref. 266F1: "Utilisation des procédés Loth pour le guidage des avions par ondes hertziennes -  Partie 1: "Étude critique des procédés Loth pour la navigation aérienne" A. Verdurand, Partie 2 "Point de vue et réfutations de la S.I.P.L."" ["Use of the Loth method for guiding aircraft with radio waves - Part 1 "Critical review of the Loth method of air navigation", Part 2 "Opinion of, and rebuttal by, the Société Industrielle des Procédés Loth (SIPL) company"], A. Verdurand, J. Blancard, in "L'Aérotechnique", Vol. 8, Nr. 137, October 1930, pp. 363-376. Source: Bibliothèque nationale de France; public domain.
• Ref. 266F2: "Le guidage des avions par câbles électriques" ["Aircraft guidance by means of electric cables"], P. Franck, A. Volmerange, in "L'Aérotechnique", Vol. 4, nr. 33, February 1922, pp. 39-47. Source: Bibliothèque nationale de France; public domain.
• Ref. 266F3: "Le câble de guidage - son emploi pour atterissage sans visibilité" ["Guidance cables - their use for landing without visibility"], Paul Larivière, in "L'Aérotechnique", Vol. 17, Nr. 190, March 1935, pp. 33-39. Source: Bibliothèque nationale de France; public domain.
• Ref. 266F4: "La Navigation aérienne par temps de brume" ["Aerial navigation during fog"], A. de Gramont de Guiche, in "L'Aérophile", Vol. 29, Nr. 1-2, 1-15 February 1921, pp. 42-45. Source: Bibliothèque nationale de France; public domain.
• Ref. 266F5: "Les câbles-guides de M. Loth - La direction des aéronefs sans aucune visibilité" ["The guide cables of Mr Loth - aircraft guidance without any visibility"], P. James, in "L'Aérophile", Vol. 30, Nr. 1-2, 1-15 January 1922, pp. 18-21. Source: Bibliothèque nationale de France; public domain.
• Ref. 266F6: "L'infrastructure aérienne" ["Aviation infrastructure"], in "L'Aéro - Organe hebdomadaire de la locomotion aérienne", Vol. 25, No. 87, No. 1301, 5 May 1933, p. 5. Source: Bibliothèque nationale de France; public domain.
• Ref. 266F7: "La navigation dans le brouillard - où en est la pose du cable Loth" ["Navigation in the fog - the status on installation of the Loth cable"], in "Les Ailes - Journal hebdomadaire de la locomotion aérienne", Vol. 4, No. 180, 27 November 1924, pp. 2-3. Source: Bibliothèque nationale de France; public domain.
• Ref. 266G: "Finding aircraft landing stations by means of audio frequency receivers", Earl C. Hanson, in "Aerial Age Weekly", Vol. 9, No. 10, 19 May 1919, pp. 489-490. Source: hathitrust.org, retrieved 20 February 2021.
• Ref. 266H: "Underwater pilot cable", p. 335 in Chapter XXVIII in in "History of Communications-Electronics in the United States Navy", Linwood S. Howeth, Bureau of Ships and Office of Naval History, 1963, 698 pp. Source: hathitrust.org, retrieved 20 February 2021.
• Ref. 266J: "Making a technology fit: evolution of the leader cable system" [complete general history, 1893 - mid-1930s], pp. 46-56 in ref. 235J, .
• Ref. 266K: "Field localizers", p. 899 in ref. 229D5
• Ref. 266L: "Simon system" [concentric burried cables for approach to landing from any direction; unsuitable for airfield with runway(s)], pp. 35-36 in ref. 235P9.
• Ref. 266M: articles in "Nature" magazine, 1921
• Ref. 266M1: "The Leader Cable System", in "Nature", Vol. 106, No. 2767, 10 February 1921, pp. 760-762. Source: nature.com, accessed 20 August 2020. [pdf]
• Ref. 266M2: ""Leader" cables for aircraft", in "Nature", Vol. 108, No. 2721, 22 December 1921, pp. 539. Source: nature.com, accessed 20 August 2020. [pdf]
• Ref. 266P: "New fog-landing system installed at Materiel Division" [US Army Air Corps, "Loth" leader cable system (with U/I keying) for landing in fog, tested at Patterson Field, Dayton/OH/USA ], in "Air Corps News Letter", Vol. XVI, No. 1. 25 January 1932, pp. 8-9. Source: Air Force Historical Support Division, retrieved 6 September 2020.
• Ref. 266Q: "An Instrument Landing System", Edward Dingley, in "Communications" (merger of "Radio Engineering", "Communication & Broadcast Engineering", & "The Broadcast Engineer"), Vol. 18, Nr. 6, June 1938, pp. 7-9, 30-31. Source: worldradiohistory.com, retrieved 11 September 2020.
• Ref. 266R: "Piloting vessels by electrically energized cables" and "Discussion", A. Crossley in "Proc. of the Institute of Radio Engineers" (IRE), Vol. 9, Nr. 4, August 1921, pp. 273-299. Source: worldradiohistory.com, retrieved 19 February 2021.
• Ref. 266S: "Blind Landing Experimental Unit" [BLEU]. Source: wikiwand.com, retrieved 28 November 2020.
• Ref. 266T: "The Portsmouth "Leader" Cable", in "The Electrical Review", Vol. 86, No. 2209, 26 March 1920, p. 392 and No. 2211, 9 April 1920, p. 458.
• Ref. 266U: in ref. 235Y10 - pp. 9-16, 18 + Fig. 8-17 (leader cable at Ford Airport / Chicago-Lansing/IL/USA, Coock principle & patent, Loth system, Cromwell-Johannson Johansson ???? method)
• Ref. 266V: "Making a technology fit: evolution of the leader cable system", pp. 45-56 in ref. 235J1 ("Blind Landing", Erik M. Conway).
• Ref. 266W: "Leader cable guidance of an experimental field gantry" [agricultural], N.D. Tillett, T.G. Nybrant, in "Journal of Agricultural Engineering Research", Vol. 45, Issue: none, 1990, pp. 253-267. Source: en.booksc.org, accessed April 2022. [pdf, See note 1]
• Ref. 268: articles about  altimeters - acoustic/sonic, electro-acoustic, capacitive, radio, radar; i.e., not atmospheric pressure based
• Ref. 268A: pp. 26-42 [FuG101, FuG101A, AN/APN-1, FuG102, FuG103, SCR-718, AN/APS-13] in "Ein Beitrag zur Flugsicherungs Geschichte" ["A contribution about air traffic control history"], Hans H. Jucker, July 2014, 61 pp. Source: www.wrd.ch. Retrieved 18 May 2020.
• Ref. 268B: "Demonstration of clearance indicator for airplanes", pp. 84 in "Bell Laboratories Record", Vol. XVII, No. III, November 1948. Source: worldradiohistory.com, accessed 17 August 2020.
• Ref. 268C: "Historic firsts: radio altimeter", pp. 18-19 in "Bell Laboratories Record", Vol. 26, No. 1, January 1948. Source: worldradiohistory.com, accessed 17 August 2020.
• Ref. 268D: "Altitude by Radio", Cass H. Maxwell, in "Popular Aviation", Vol. XXVI, Nr. 2, February 1940, pp. 44-46, 94.
• Ref. 268E: "A Terrain Clearance Indicator", Lloyd Espenschied, R.C. Newhouse, in "The Bell System Technical Journal", Vol. XVIII, No. 1, January 1939, pp. 222-234. Source: worldradiohistory.com. Accessed 22 August 2020.
• Ref. 268F: "1967 Pioneer Award - Lloyd Espenschied, Russel Conwell Newhouse" [radio altimeter], Robert I. Colin, in "IEEE Transactions on Aerospace and Electronic Systems", July 1967, pp. 736-742. [pdf]
• Ref. 268G: "Funkhöhenmesser FuG 101a mit Frequenzmodulation" ["Radio altimeter FuG 1010 with frequency modulation"], Hans Jucker, 6 pp. Source: cdvandt.org, accessed 22 August 2020. Also see pp. 26-32 in ref. 268A.
• Ref. 268H: "Elektrischer Höhenmesser FuNG 101 - Kurzbeschreibung und Betriebsvorschrift E 93001" ["Electrical altimeter FuG 101 - description and operating instructions"], Luftfahrtgerätewerk Hakenfelde GmbH, 21 pp. Source: cdvandt.org, accessed 22 August 2020.
• Ref. 268J: "The sonic altimeter for aircraft" [history and status of the sonic altimeter], C.S. Draper, National Advisory Committee for Aeronautics, Technical Notes No. 611, August 1937, 127 pp. [file size: 74 MB; Abstract]. Source: NASA Technical Reports Server (NTRS), accessed 22 August 2020.
• Ref. 268K: "Pursuiters test sonic altimeter", in "Air Corps News Letter", Vol. XVI, No. 1. 25 January 1932, p. 14. Source: afhistory.af.mil, accessed 6 September 2020
• Ref. 268L: see ref. 235Y10 - pp. 16, 17 (acoustic, electro-acoustic, Behm System), p. 17 (radio), pp. 17-18 & Fig. 19 (capacitive).
• Ref. 268M: see ref. 6H ("Radio and radar equipment in the Luftwaffe - III: Electric altimeters")
• Ref. 280: Articles about bombing in general, incl. bomb aiming, bomb sights, and bomb trajectories
• Ref. 280A: Articles about the 1912 "Aéro-Cible Michelin", other 1912 bomb-aiming competitions, and bombing aspects, from the 1912 volume of "L’Aérophile - Revue technique & practique des locomotions aériennes - Bulletin officiel de l'aéro-club the France" ["Technical & practical review of aerial propulsion - Offcial bulletin of the Aero Club of France", 1893-1947]
• Ref. 280A1: "Prix de l’Aéro-Cible Michelin" ["The "Aéro-Cible Michelin" Prize"], in "L’Aérophile", Vol. 20, No. 3, 1 February 1912, p. 19. [First round will take place at Châlon, Feb 4 & 11, 1912. Target to have a 20 m radius (66 ft), marked by pickets spaced 2 m (6.5 ft) around the roped perimeter; 50 minutes per participant.]
• Ref. 280A2: "Autour du Concours de "L'Aéro-Cible Michelin"" ["About the Aéro-Cible Michelin competition"], Henri Mirguet, in "L’Aérophile", Vol. 20, No. 4, 15 February 1912, p. 76. [The result of the first round of the competition was “negative”: not a single hit of the target.]
• Ref. 280A3: "Une lance-bombes pour Aéroplanes et Dirigeables" ["A bomb-releaser for airplanes and dirigibles"], Robert Letelier, in "L’Aérophile", Vol. 20, No. 4, 15 February 1912, p. 87, 88. [Manual bomb release mechanism + photos thereof; trajectory diagrams per USN Lt. Riley E. (Estel) Scott]
• Ref. 280A4: "L'avion de guèrre" ["The war plane"], Henri Murguet, in "L’Aérophile", Vol. 20, No. 6, 15 March 1912, p.124. [Results of the first round of the Concours de “L’Aéro-Cible Michelin” were “not exactly brilliant”]
• Ref. 280A5: "L'Aéro-Cible Michelin", in "L’Aérophile", Vol. 20, No. 7, 1 April 1912, pp. 163. [Second round of the competition: supposed to take place on 24 March 1912 at Camp de Châlons, postponed to 21 April due to strong wind gusts. Three participants (2 military, 1 civil – with "Scott" bomb release device). Target (now) 20 m diameter. "Bomb" of 7.1 kg (15.7 lbs), 16 cm (6.3 inch) diameter.]
• Ref. 280A6: "L'Aéro-Cible Michelin", Robert Letelier, in "L'Aérophile", Vol. 20, No. 9, 1 May 1912, pp. 200, 201. [Report on first round of the series for the Prix de L’Aéro-Cible Michelin, 15 bombs each, 20 m diameter target, minimum altitude 200 m, photo of bomb hanging from airplane]
• Ref. 280A7: "L'Aéroplane, arme offensive – l’appareil de pointage" ["The airplane – offensive weapon – the aiming device"], Alex Dumas, in "L’Aérophile", Vol. 20, No. 10, 15 May 1912, pp. 223, 224. [The "Aéro-Cible Michelin" raised the issue of using the airplane as an offensive war machine. Bombers have to stay above the 500 m (1600 ft) height range of anti-aircraft artillery / gun fire. Increasing altitudes, so need to know more about bomb trajectory.]
• Ref. 280A8: "L'Aéro-Cible Michelin", in "L'Aérophile", Vol. 20, No. 12, 15 June 1912, p. 284. [Results of the competition on 26 May and 8-9 June, at Mourmelon [ = Camp de Châlons]. On 8 June, civilian Louis Gaubert with USN Lt. Scott as bomber, with his bomb release device, hit the target with 10 of 16 projectiles, but was disqualified for flying below 200 m).]
• Ref. 280A9: "Prix de 25.000 francs de l'Aéro-Cible Michelin - Prix de 50.000 francs de l'Aéro-Cible Michelin" [], Vol. 20, No. 15, 1 August 1912, p. 359. [Final rounds of the competition scheduled for 27-27 July and 10-11 August 1912 at Camp de Châlons. Prizes equivalent to appr. 80 and 160 thousand euros in Jan-2022. Source: france-inflation.com]
• Ref. 280A10: "L'Aéro-Cible Michelin", in "L'Aérophile", Vol. 20, No. 17, 1 September 1913, p. 400. [9 ,10, 15 August round of the competition: target 120x40 m (size of a dirigible airship hangar) and drops from 800 m (2600 ft) minimum altitude.]
• Ref. 280A11: "Résultats de l'Aéro-Cible Michelin 1912", in "L'Aérophile", Vol. 20, No. 18, 15 September 1912, p. 432. [Overall 1912 winner is civilian Louis Gaubert]
• Ref. 280A12: "Aéro-Cible Michelin 1912 : attribution des prix de 50.000 et 25.000 francs" ["Award of the 50 & 25 thousand francs prizes"], in "L’Aérophile", Vol. 20, No. 19, 1 October 1912, p. 454. [15 August. Winner (Louis Gaubert, civilian) hit the 20 m diameter target with 12 of 15 projectiles, from 200 m altitude.]
• Ref. 280A13: "L’Aviation en Allemagne - Concours de lancement de projectiles et d’applications militaires en aéroplane" ["German aviation - projectile dropping competition and military airplane applications"], in "L’Aérophile", Vol. 20, No. 19, 1 October 1912, p. 445, 446. [Military competition at Gotha/Germany, 17-19 August. Organized by the Deutscher Fliegerbund and the Reichsflugverein. Stationary ground target 100x100 m, 7.1 kg dummy bombs, minimum altitudes 200 m, 400 m (target size + 50%), and 600 m (target size + 100%); moving target (tethered balloon, 30 m long, 3 m diameter, 4 m above ground) from minimum 50 m altitude; intercepting a dirigible.]
• Ref. 280B: articles about bomb sights
• Ref. 280B1: "Deconstruction the myth of the Norden bombsight", Michael Tremblay, University of Victoria/BC/Canada, Master of Arts thesis, 2007, 150 pp. Source: library.uvic.ca, retrieved 30 June 2021.
• Ref. 280B2: "The bombsight", in "US Air Forces At War", special issue of "Flying", Vol. 33, No. 4, October 1943, pp. 103-107, 342-344.
• Ref. 280B3: "Notes on enemy bombsights" and "Notes on enemy bombsights (concluded)", F. Poslethwaite, in "Aircraft Engineering and Aerospace Technology", Vol. 14, Nr. 9, September 1942 [pdf] , pp. 244-247, 250 and Vol. 14, Nr. 10, October 1942, pp. 276-280 [pdf]. Source: en.booksc.org, &  en.booksc.org respectively. Retrieved 30 June 2021.
• Ref. 280B4: "Close-up of the Norden bombsight", Volta Torrey, in "Popular Science", Vol. 146, No. 6, June 1945, pp. 70-73, 220, 224, 228, 232.
• Ref. 280C: articles about bomb trajectories
• Ref. 280C1: "Der Bombenabwurf" ["The bomb drop"], Bachofener, in "Allgemeine schweizerische Militärzeitung = Journal militaire suisse = Gazetta militare svizzera", Vol. 82, Nr. 1, January 1936, pp. 296-304. Source: e-periodica.ch, retrieved 18 June 2021.
• Ref. 280C2: "Bomb trajectories", Edwin Bidwell Wilson, National Advisory Commission on Aeronautics (NACA), Technical Report No. 79 (NACA-TR-79; reprint from 5^th annual report), 1920, 9 pp. Source: ntrs.nasa.gov, retrieved 28 June 2021.
• Ref. 280C3: "Weapon Delivery Analysis and Ballistic Flight Testing", R.J. Arnold, J.B. Knight, Vol. 10 of "AGARD Flight Test Techniques Series", Advisory Group for Aeronautical Research and Development (AGARD), North Atlantic Treaty Organization (NATO), AGARDOgraph 300, Technical Report RDP, 1 July 1992, 172 pp. Source: www.sto.nato.int, retrieved 21 June 2021.
• Ref. 280C4: "Theory of horizontal bombing", pp. 233-234 in Section D of "Aircraft fire control", in Chapter 23 of "Fire Control", Vol. 2. of "Naval Ordnance and Gunnery", Dept. of Ordnance and Gunnery, United States Naval Academy, Bureau of Naval Personnel (ed.), NAVPERS 10798-A, 1958 revision of the 1950 edition, 508 pp. Source: eugeneleeslover.com, retrieved 21 September 2021.
• Ref. 280D: articles about bombing & military aviation in general
• Ref. 280D1: "Clément Ader, inventeur d’avions" ["Clément Ader, inventor of airplanes"], Pierre Lissarague, Bibliothèque Historique Privat (publ.), 1990, 320 pp., ISBN-10: 2708953559.
• Ref. 280D2: "The socio-technical construction of precision bombing: A study of shared control and cognition by humans, machines, and doctrine during World War II" [file size: 47 MB], Raymond P. O'Mara, PhD thesis at the Massachusetts Institute of Technology (MIT), June 2011, 368 pp. Source: mit.edu, retrieved September 2022. [pdf, file size: 13 MB].
• Ref. 280D3: "La militarisation de ciel" ["The militarization of the sky”], pp. 8.9-8.23 (pdf pp. 342-365) in "Août" ["August"], Chapter 8 in "L’année aéronautique 1912 à travers le quotidien Le Petit Parisien" [file size: 174 MB] ["The aeronautical year 1912 seen through the daily newspaper Le Petit Parisien"], Joel Vergne, Yves Meusburger (ed.), Collection Mémoire de l'Aviation Civile, Direction Générale de l'Aviation Civile (DGAC), 2013, 2015, 760 pp. Source: calameo.com, accessed 9 January 2022.
• Ref. 280D4: "Gli ufficiali aviatori iniziano la guerra nuova gettando bombe in un accampamento nemico" ["Airmen officers start the new war by dropping bombs at an enemy camp"], on the frontpage of "La Stampa" newspaper, Vol. XLV, Nr. 304, morning edition of Thursday 2 November 1911. Source: archiviolastampa.it, accessed 10 January 2022. A transcript and Google translation to English (with improvements/corrections by me) is here.
• Ref. 280D5: "Pour que nous ayons des aéroplanes" ["So that we shall have areoplanes"], open letter to the editor-in-chief by André Michelin, in "Le Matin" newspaper, Vol. 28, Nr. 10145, 7 December 1911, p. 1. Source: Bibliothèque de France (BNF) on-line library, accessed 13 January 2022.
• Ref. 280D6: p. 176 in "Aeroplanes and airships as national and collective symbols in Western Europe before the First World War (1908-1914)", Florian Schnürer, in "Memoria y Civilización", Vol 12, 2009, pp. 155-189. Source: Universidad de Navarra, accessed 12 January 2022
• Ref. 280D7: "Dirigibles in Tripoli War - Drop bombs among Turks", in "The New York Times", 7 March 1912, p. 4.
• Ref. 280D8: "Aeroplanes in Tripoli War", in "Flight - First Aero Weekly in the World", No. 191 (Vol. IV, No. 34), 24 August 1912, p. 784. Source: archive.org, accessed 17 January 2022.
• Ref. 280D9: "Foreign News - Tripoli", in "Aircraft", Vol. 3, No. 2, April 1912, p. 46. Source: archive.org [file size: 48 MB], accessed 17 January 2022.
• Ref. 280D10: p. 290, 291 in "Practical military aviation", J.H. Worden, in "Aircraft", Vol. 3, No. 10, December 1912, pp. 289-291. Source: archive.org [file size: 48 MB], accessed 17 January 2022.
• Ref. 280D11: "A history of aeronautics" [file size: 35 MB], Evelyn Charles Vivian, William Lockwood Marsh; Harcourt, Brace & Co. (publ.), 1921, 521 pp.
  Source: archive.org, retrieved 17 January 2022.
• Ref. 280D12: "Strategic bombing before 1939", "The British Strategic Air Offensive against Germany in World War II", "The American Strategic Air Offensive against Germany in World War II", Chapter 1 (pp. 11-90), Chapter 2 (pp. 91-182), Chapter 3 (pp. 183-252) in "Case Studies in Strategic Bombardment" [file size: 80 MB, a good-but-reduced-resolution pdf file is here, 11 MB], Alvin D. Coox, Richard G. Davis, R. Cargill Hall, Thomas C. Hone, William A. jacobs, Lee Kennet, Stephen L. McFarland, David MacIsaac, Wesley Phillips Newton, Richard J. Overy, Steven L. Rearden, US Air Force Historical Studies Office, 1 January 1998, 679 pp. Source: US Defense Technical Information Center (DTIC), dtic.mil, retrieved 18 June 2022.
• Ref. 280D13: pp. 17-23 in "De Clément Ader à Gagarine", Luis Castex, Librairie Hachette (publ.), 1967, 342 pp.
• Ref. 280E: legal aspects of bombing, international treaties, etc.
• Ref. 280E1: pp. 264, 265, 280, 281, 438, 439 in "The Proceedings of the Hague Peace Conferences - Translation of the Official Texts - The Conference of 1899", Div. of International Law of the Carnegie Endowment for International Peace, Oxford University Press (publ.), 1920, 905 pp. English translation of the 1907 edition by Martinus Hijhoff (publ.) of the original proceedings of the 1899 Conference by the Foreign Office of The Netherlands: "Conférence internationale de la paix. La Haye, 18 mai - 29 juillet 1899. Ministère des affaires étrangères. La Haye, 1899". Source: US library of Congress, retrieved 2 January 2022.
• Ref. 280E2: "Protecting Civilians from the Effects of Explosive Weapons - An Analysis of International Legal and Policy Standards", Maya Brehm, United Nations Institute for Disarmament Research (UNIDIR), August 2018, 185 pp. [pdf]
• Ref. 280E3: "The 1923 Hague Rules of Air Warfare - A contribution to the development of international law protecting civilians from air attack", Heinz Marcus Hanke, in "International Review of the Red Cross", Vol. 33, Issue 292 , February 1993, pp. 12 - 44. [pdf]. Note: the original text of this article was published in the May-June 1991 German-language issue of the International Review of the Red Cross (No. 3, pp. 139-172).
• Ref. 284: "Report on interrogation of C.S.O., Luftflotte Reich Schleswig (General Bohne) and those available of his technical staff", D.C. Nutting, Report No. R-169/RAF, Air Technical Intelligence (A.T.I.) Headquarters, 2nd Tactical Air Force (T.A.F.) (M), 28 May 1945, Declassified IAW EO 13526, 15 pp. [Keywords: ground radar (Elefant, Jagdschloß, Forsthaus, Jagdhütte, Jagdhaus, Heidelberg, Tannenbaum, Freya Fahrstuhl, Naxos, Korfu, ground jamming (Anti-Bumerang/OBOE, Anti-Rotterdam/H2S), airborne radar (SN2, SN3), aids to automatic weapon-firing (Elfe, Grom, Pauke-Pauke, Berlin N, Bremen-O, FuG-244, FuG-245), homing devices (FuG-221, Naxos, SN3 Biene), IFF (Allied IFF, FuG-226 Neuling, Infra-Red IFF), airborne infra-red (Falter, Kiel), airborne radio (FuG-224), navigational aids (Komet, Hyperbel, Bernhard/Bernhardine, Hermes/Hermine, Erika), German A.T.I. (organisation, crashed aircraft)]. Source: The National Archives of the UK, used in accordance with the Open Government License [pdf].
• Ref. 292: "Führungs- und Navigationsverfahren, Bordfunksprech- und Bordfunknavigationsgeräte, Bordfunkmeßgeräte, Eigener und feindlicher Hochfrequenzeinsatz, Störsender, feindliche Bordfunkmeßgeräte, Feindliche Navigationsverfahren, Stand 1.1.1945", 6 pp. Source: TBD.
• Tables: Guidance & navigation methods (UKW-Peiler; Y-Anlage; Egon; Bernhard-Anlage; Jagdhütte; Bodentruhe-Anlage; Sonne-Anlage); Radio telephony & navigation equipment (FuG 16ZY; FuG 15, FuG 125; FuG 24 SE; FuG 120, FuG 130, FuG 29, FuG 123); On-board radar (FuG 220 / Li SN2; FuG 228 / Li SN3; FuG 218 VR / Neptun VR; FuG 218 QR / Neptun QR; FuG 240 / Berlin N 1a; FuG 244 / Bremen O; FuG 200 / Hohentwiel; FuG 224 / Berlin A; FuG 217 / Neptun RII; FuG 25a / Erstling; FuG 227 I-III / Flensburg; FuG 350 Z/ZX, Naxos Z/ZX, Naxos ZR; FuG 280 / Kiel; Falter), Luftlageaufklärung (Wassermann MI-MY, Elefant, Klein Heidelberg, Freya, Würzburg Riese, Jagdschloß, Forsthaus F, Jagdschloß Michael B, Jagdschloß Z / Forsthaus Z, Jagdwagen, Korfu/Naxos/Naxburg); Jammers (Heinrich I & II, Karl I & II, Feuerstein I & II, Feuerzange, Feuerhilfe, Feuerland I, Abfrage-Ballstörgerät, Roland I & II, Klystron Röhre); Enemy on-board radar (Rotterdam/Rotterdam-X/Belfort/Meddo, ASV/ASD/Rotterdam, Luchs/Grille/Frankfurt, Monica/Luchs/Fish Pond, Village-Inn); Enemy radio navigation systems (Hyperbel, Long Range, Bumerang, Diskus, Mikro-M). Status of 1 January 1945.
• Ref. 293: "Bernhardine" FuG120k documentation at the National Air and Space Museum (NASM), Washington/DC/USA, archive ref. R2219F763.
• Ref. 293A: "Bordfunkanlage - Baumuster FuG 120 k" ["On-board radio system - Model FuG 120 k], RE 3523, Reichsluftfahrtministerium (RLM), sheet 1 of 1, no sign-off, no date.
• "Leitungsaufstellung, Einbaugeräte" ["list of 18 wires/cables, 8 equipment items"]
• Ref. 293B: "F-Geräte - Schreibverstärker SV 120k, Stabilisatorkasten Stk 120k, Verteilerleiste VL 120k, Umschaltgerät UG 120k", Reichsluftfahrtministerium (RLM), 4 sheets, no sign-off, no date.
• Outline drawings, dimensions, and weights of the equipment items; all items supplied by Telefunken G.m.b.H., in Berlin-Zehlendorf.
• Ref. 293C: "EB8-Schaltbild 235 - Schaltplan der Anlage FuG 120 k in Verbindung mit RE 3525" ["EB8 Schematic 235 - Circuit diagram of the FuG 120 k system, combined with RE 3525"], 1 sheet, signed 20 December 1944, 25 & 26 January 1945.
• FuG120k (Psch120a, SV 120k, UG 120k, SpK1), FuG 16ZY, FuG 125, FuG 120k, FuG 29, PR-16, VK 16 Za, AR Z16, AZ G3, SFN 1, UF 17, AD 18Yb, RV 3, AAG 16Z-3, AAG 16E-1, FA 16 E-4, LR 3a, LR 3, EBL3F, FBG 16, FBGF2, LK VIII.
• Ref. 294, etc: to be allocated.

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