©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 (made into separate page; 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).

red-blue line


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

Lorenz-Scheller A/N system

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

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

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

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

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

Lorenz-Scheller A/N system

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

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

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

Lorenz-Scheller A/N system

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

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

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

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

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

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

Optical airway beacons

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

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

under construction

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

Aero Radio Nav

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

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


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

Scheller patent

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

(source: German patent 201496 and US patent 2172365)

under construction

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

  • In US, contrary to Europe, RadNav R&D almost exclusively by various branches of the federal government, instead of private industry.
  • US developments reinvented Schellers system, but US Army Air was fully aware of his patents when they took over ca 1926.
  • Four-Course Range system, Low-frequency Radio Range (LFR) ; a characteristic of the low-frequency range was the Cone of Silence immediately above the station (cf. 3D radiation pattern in Fig. 62 above).
  • Ref. 185C3. Ref. 185F: 22 A/N "signals" [ = characters] per minute [TBC: 22x A + 22x N or 11+11]; interrupted every 15 min for station identification by voice from the omni-directional co-located radiotelephone station.
  • Here, the word "range" is used in the sense of area of open land, e.g., a site for testing equipment. I.e., not in the sense of "distance" (as in the acronym "radar"). Radio ranges do not provide proper distance information, though strength of the received signals (relative field strength) provides some indication of relative distance.
  • "A" / "N quadrant (clean A/N); "A"/"N" twilight zones = bi-signal zone; on-course / equisignal zone; "cone of silence" [add illustration, w/wo "fill in" beacon] over the beacon range ca 100 miles, 1:60 rule of thumb (arctangent of 1° ≈ 1/60) --> 1° triangle --> 1 mile lateral for every 60 miles distance, so a 3°-wide equisignal zone is roughly 3x1=3 miles wide at 60 miles from the beacon, or about 5 miles (4+ NM) at the 100 miles range limit, more difficult to accurately track to course line
  • NBS "cone of silence markers", a.k.a. "Z" markers. First installed experimentally 1934/35, improved 1936/37 by NBS incl. 75 MHz, 3 kHz AM, 7 W. 93 MHz + 60 Hz AM, but 75 MHz for dev of US AAC ILS at Wright Field. Two crossed horizontal dipoles, installed above a ground screen surface.
  • Tests by/at Bureau of Air Commerce, Army:
  • 1923, at National Bureau of Standards Washington/DC: two 1-turn loops, 43.75x15.25m/150x50ft, 36.5°/143.5° crossing angle, 2 kW quenched spark transmitter, A/N, loops tuned to 300 kHz; ref. 229E1.
  • McCook field @ Dayton , ref. 229N.
  • Wilbur Wright field (Wright Patterson), ref. 229N.
  • Typically, multiple airways that lead to/from the same city/airfield/intersection do not cross at right ( = 90°) angles. Also, airway courses are typically also not aligned with north/south and east/west. Therefore, the courses of a Radio Range are typically rotated simultaneously, and bent or shifted (ref. 229Q, pp. 36-43):
  • "course rotation": changing the all courses of a Radio Range by the same amount and in the same direction, i.e., without changing the angles between the course-pairs. (as proposed in Ottos Scheller's patent - most elegantly done with a radio goniometer).
  • "course bending": changing the angle between the two opposite courses of a course-pair, from their normal 180° angle. Typ. by no more than 30°, i.e., to 150-210°.
  • "course shifting": changing the angle between the two course-pairs of a radio range from the standard 90°+90°. Typ. by no more than 30°, i.e., to 60°+120°.
  • The Aeronautics Branch standardized a type of 4-Course Radio Range during the course of 1928.
  • Loop type ranges vs tower (simultaneous voice) type ranges, incl. (dis)advantages: p. 13 ref 229W5.
  • Visual-Aural Range system (VAR), 4-course beacon; a 4-course range, comprising a 2-course Aural Range and 2-course Visual Range; "visual", as it provided on-beam/deviation to the pilot via an indicator instrument, rather than via sound on his headphones.
  • Per ref 185F pp. 37ff: constant tones of diff audio modulation freq, instead of A/N keying. 65 & 86.7Hz (originally 60 & 85 Hz, but abandoned due to....) 86⅔, per ref. 229R4-No.6; originally ) and 75 & 100 Hz. Marker beacons transmitting ID code sigs , primarily to ID intersections of courses from adjacent ranges, "double frequency" marker beacons, alternating between the two. Single -freq beacons used to mark emergency landing fields, abrupt terrain elevation changes, dangerous landmarks; 5 miles max range. Marker beacon freq same as associated Radio Range freq. Marker stations also low power radiophone station, for emergency communications or emergency WX broadcast. Air nav facilities operated on freqs 237-285 kHz (LW) and 315-350 kHz (MW), with 6 kHz channel spacing.
  • Note: per Article 5 of the Regulations of the 1927 "International Radiotelegraph Conference" that took place at Washington/DC, the 285-315 kHz band (ca. 1050-950 m wavelength) was exclusively allocated to radio beacons, effective 1 January 1929. The 237-285 kHz segment was part of the 194-285 kHz band that was shared by Air Mobile Services, Air Fixed Services, Government Fixed Services, and broadcast (in Europe only).
  • one Visual Range system with two course lines (150 Hz and 90 Hz tones, visual indicator in the cockpit, full meter needle deflection for ≥ 10° off-beam deviation)
  • one Aural Range system with 2 course lines (1020 Hz A/N system); equi-signal beam appr. 1½-2° wide.
  • First demonstrated in 1937 by the Bureau of Air Commerce (VHF, 63 MHz), operational in the US from 1944 - 1960 (VHF, 112-118 MHz).. Also used in Australia, operational 1947 to at least 1980
  • Lorenz' 1938 Swiss patent 206464: Motorized rotating antenna arrangement of 2 pairs of vertical antennas (grounded monopoles or dipoles) at corners of a square, Adcock arrangement, simultaneously fed by transmitter via , central vertical monopole, fed simultaneously by same transmitter; creates rotating equi-signal beams; using shortwave to obtain long range.
  • Lorenz A/N AFF, "blind landing system"
  • adopted in Britain via Lorenz/ITT as the Standard Beam Approach System (SBAS) - indeed, it was.
  • ILS (Localiser & Glideslope),
  • First: curved constant-signal-strength glide path (not slope!). Add references for assessment of curved path. Lorenz LOC used (but not in UK), as such, i.e., no separate glide beacon (which would also have implied additional receiver + antenna(s) in/on aircraft.
  • Using a separate glide path/slope equisignal beacon was first conceived and then patented by Ernst Kramar (Lorenz) in 1937 (German patent 734130, and equivalent 1939 Kramar/Hahnemann (Lorenz) US patent 2210664). Use ref. 263D2 + Fig! Make separate subsection for GP/GS. Curved glide path forced the pilot to constantly adjust power setting and pitch attitude. This is considered very poor piloting practice, as, ideally (incl. no wind variation) an approach, once established, basically hands-off - until flare (UK: round-out). Eventually, equisignal radiation pattern adjusted/adapted to include curve-to-touchdown. Note: Lorenz & US curved glide path initially not critical, with very slow aircraft (one could basically keep up with a Ju-52 on a bicycle) with very soft / very large-compression-stroke landing gears. Also: Kramar/Gerbes DRP 720890, ref 229L20
  • A variation with a separate Lorenz beacon abeam the touchdown zone was patented in 1940 by Andrew Alford (IT&T, parent company of Lorenz, US patent 2294882).
  • SCR51: by ITT, parent company of Lorenz.

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

BoS loop antennas

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

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

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

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

BoS loop antennas

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

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

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

BoS loop antennas

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

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

4-course radio range

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

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

4-course radio range

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

(source: adapted from ref. 229M)

A/N system

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

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

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

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

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

Four-course AN beam sound...

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

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

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

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

(source: © ipse)

4-course radio range charts

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

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

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

4-course radio range

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

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

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

4-course radio range

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

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

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

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

12-course radio range

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

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

12-course radio range

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

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

4-course radio range

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

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

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

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

VHF Glide Path antenna

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

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


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

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

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

yagi uda

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

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

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

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

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

Uda-Yagi examples

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

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

Phase array antenna

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

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

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


under construction

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

In 1913/1914 Leo Pungs and Felix Gerth (both at C. Lorenz AG) developed the first practical and satisfactory method for amplitude modulating the RF antenna current of high power transmitters with voice and music. It used a choking coil on a closed laminated iron core. The series-impedance of that coil was controlled by varying the magnetic saturation level of the core via the DC current through a secondary coil on the same core. This was referred to as a "telephony choke" or "Pungs choke" ("Steuerdrossel", "Pungs-Drossel"; ref. 263E). The concept was originally proposed by Reginald Fessenden around 1902, who never got it to work properly. In 1913 Ludwig Kühn of the Dr. E.F. Huth company in Berlin revived the method (cf. 1923 US patent nr. 1653859). By hard-switching between zero and full saturation, this type of choke coil could also be used as an on/off telegraphy keying-choke ("Tastdrossel"), i.e., as an RF switch, instead of an AM modulating choke.

Lorenz LW rotable beacon Eberswalde

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

(source: adapted from ref. 2)

Lorenz LW rotable beacon Eberswalde

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

(source: ref. 2)

Lorenz Eberswalde

Fig. 76B: The Lorenz experimental radio site at the former "Bullenwiese" common grazing field at Eberswalde - 1918

(source: ref. 263E)

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

corporate Lorenz ITT ATT

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

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

Lorenz Co: also ref. 263D2.

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

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

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

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

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

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

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

Lorenz-Schiller A/N system

Fig. 77: Circuit diagram and top view of the transmitter modulating & keying unit)

(source: adapted from Fig. 3, 24 and §76 in ref. 235V5)

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

Kiebitz vertical dipole

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

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

Lorenz-Schiller A/N system

Fig. 79: Concept of opening/closing reflectors to create complementary dot & dash beams

(source: ref. 31)

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

Two overlapping "Scheller" beams with equisignal zone:

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

The 1937 patents of Lorenz/Kramar expand this scheme with a complementary-keyed (e.g., E/T) beam system for vertical guidance. This [the latter?] was simply re-patented in 1940 in the USA by others (ITT paremt company?? patent nr ??)

front course, back course - To fly the back course inbound, the pilot must revert L/R mentally or switch the instrument (polarization), or the beam keying of the beacon station must be inverted, when active crs changed.

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

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

Lorenz Localizer ET-beam

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

(sources: ref. 2A2 & 235A (left, Telefunken), ref. 31 (center), ref. 137B / 225C2 / 235P26 (Lorenz, at Berlin-Tempelhof airport))

Lorenz Localizer ET-beam

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

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

Lorenz beam station

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

Lorenz beam station

Fig. XX: Reflector relay box of the Lorenz beam antenna system installation - front cover removed

(source left image: Fig. 43 & §89 in ref. 235V5; right image: ref. 2A2, p.95)

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

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

Lorenz Localizer ET-beam

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

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

The marker beacon antennas were standard 1/2-wavelength horizontal dipoles. So, for 38 MHz, they had an overall length of about 3.75 m (≈ 12.3 ft). The transmitter was placed in a large "dog house" at the base of the antenna. A chicken-wire ground plane of ca. 3.5x8 m extended about 1/2 wavelength to the left and right of the dipole. It shielded the transmitter and also made the antenna's radiation pattern less dependent on the local soil conditions. The dipoles were aligned with the runway's centerline, and installed about 1/4 wavelength (≈ 1.8 m, ≈ 6 ft) above the screening (ref. 235V5, §90 and Fig. 44).

Lorenz Localizer ET-beam

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

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

Lorenz Localizer ET-beam

Fig. XX: The transmitter and control unit of the Lorenz beacon ground station (1935)

(source: adapted from ref. 229A7; items not shown to same scale)

Lorenz Localizer ET-beam

Fig. XX: The equipment items of the Lorenz beacon receiver system installation in the aircraft

(source: adapted from ref. 235Q)

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

Lorenz beam landing procedure

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

(source: adapted from ref. 31)

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

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

Lorenz instruments

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

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

Lorenz instruments

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

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

Lorenz instruments

Fig. XX: Rear view of the landing beam indicator - one neon lamp removed

(source: adapted from ref . 235V3, 235V4)

The glide path meter has an uncalibrated sclae. The instrument scales and the designations L, R, O, and I are self-luminous (typ. radium paint).

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

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

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

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

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

In 1936/37, Lorenz installed its beam systems at three aerodromes around London: Heston, Croydon, and Gatwick. Sept 1936: operational at Heston (First airline demo by British Continental Airways, on 21 May 1936, with the only British air transport airplane appropriately equipped; at that time, experimental test phase at Croyden not yet finsihed) , decided to proceed with installation at Croydon, order placed for installation at Gatwick; all installed by Standard Telephones & Cables, Ltd. (British subsidiary of Lorenz parent company ITT, see Fig. XXX). Ref. 235B2, 235B4, 235B5, 235P6. VHF beacons of the Lorenz/Standard Telephones & Cables, Ltd., Plessey, and Marconi companies were installed at Croydon for/by the British Air Ministry tests and the medium wave beacon [ = 4th beacon] (at Croydon) was been modified for aural operation.

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

Alos: ref. 263D2, p. 159.

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

Lorenz AWA

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

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

Lorenz STC Australia

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

(source: ref. 229P2)


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

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

kicking meter signals

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

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

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

kicking meter signals

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

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

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

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

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

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

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


under construction

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

Luftwaffe AFFA

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

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

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

In 1943, the German Luftwaffe appears to be the first to have considered a beam landing system for installation on aircraft carriers (ref. 244T) - obviously based on the standard Lorenz-system.


Early 1939, the Luftwaffe ordered several beacon systems from the Lorenz A.G., for long(er) range air navigation: a range of 300-600 km. The purpose of this system was fighter guidance, by keeping the equi-signal guide beam pointed at a group of enemy aircraft. This would also relieve radio communication frequencies.These beacon systems had the code name "Karussel". Two were constructed: one near the town of St. Peter, the other in List on the isle of Sylt - both in the far north of Germany. These two stations were supposed to become operational October/November of 1939 (ref. 230Q8). However, this may not have happened until early 1940 (ref. 2B, p. 64). Also, the actual location in/near St. Peter is unconfirmed. The town has four parts (St. Peter-Böhl, St. Peter-Dorf, St. Peter-Bad, and St. Perter-Ording), and local historians have no info on this station.

It appears that a third Karussel was built on the nearby Frisian isle of Wangerooge (ref. 2B, p. 64-66, 174), some 75 km southwest of St. Peter,  only to be moved to Nunspeet in The Netherlands around mid-1940, without having been tested.

Knickebein locations

Fig. 7X: Location and beam-pointing direction ranges of the Karussel stations (and initial Knickebein stations)

(source: adapted from ref. ref. 230Q8)

The system was developed 1939 by Goldmann et al at Lorenz AG, as a rotable "improved landing beacon" system. It was an interesting adaptation of the standard Lorenz civil landing-beam system. It used that beacon's standard 500 W transmitter, which compatible with the Luftwaffe's FuBl1-FuBl3 landing beacon receivers (30-33.3 MHz, i.e., a wavelenght λ of 9-10 m). The standard short-range landing beacon had a single half-wavelength (½ λ) vertical dipole that continously transmitted a radio signal with a 1150 Hz tone. This dipole had a vertical reflector (= passive) to the left and to the right of it (see Fig 77). These reflectors where enabled alternatingly, with a complementary keying rhythm: 1/8 sec "dot" and 7/8 sec "dash" (equivalent to the Morse characters "E" and "T"). The antenna radiation pattern of the standard landing beacon was symmetrical in the front and back pointing directions. To significantly increase the range, "Karussel" needed a high-gain antenna system that concentrated the transmitter energy in the forward pointing direction of the beacon. It comprised three vertical dipole antennas in parallel, spaced by 0.7 λ. The center dipole was continuously energized by the transmitter. The two adjacent dipoles were energized in the standard E/T rhythm. Each dipole had a passive reflector behind it, at a distance of 1/4 λ. The initial configuration had one passive director in front of each dipole. The final version had two directors, at 0.4 λ and 0.8 λ in front of each dipole. This made the two foreward sub-beams of the radiation pattern narrower and stronger ( = increased range), at the expense of creating more side-lobes. This antenna configuration can be described as three vertical 3- or 4-element Yagi-Uda beam antennas in parallel - a clear precursor to modern-day ILS Localizer antenna systems. The radiation pattern had a 2° wide main equisignal guide beam, and additionals beam that were offset by 40° to the left and the right of the main beam.

Lorenz Karussel

Fig. XX: Antenna configurations of the standard Lorenz landing beam beacon and of the "Karussel" beacon

(source: initial config. adapted from ref. 2B, p. 65; final config. adapted from ref. 230Q8)

Lorenz Karussel

Fig. XX: A "Karussel" beacon (location unknown) and the associated radiation pattern

(source: adapted from ref. 2B, p.65; antenna system = 3x "vertical dipole + reflector + 2 directors")

To make the antenna system rotable, a turn-table construction was used ("Richtantennendrehgestell"). The 3 x 4 wooden antenna masts were mounted on a steel truss platform of 14x14.5 m (46x47.6 ft). It rotated on a circular steel track with a diameter of 13 m (42.7 ft). The track was supported by concrete blocks. The platform was rotated with a manual winch. The transmitter hut ("Senderbaracke") was located 30 m away from the antennas, and connected via a 2-wire transmission line ("Zweidrahtleitung", "Lecherleitung"; ref. 2B). Ref. 2B (p. 64), ref. 230Q8.

Lorenz Karussel

Fig. XX: Top, side, and cross-sectional view of the turn-table structure of the Lorenz "Karussel" antenna system

(source: adapted from ref. 230Q8, September 1939)

Check: ref. 2C3, p. 107.


under construction

LW/MW "Marconi" range in Australia.

LW/SW Philips equsignal beam beacons


under construction

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

Civil use/mktg/prod(?) in UK already via Lorenz sister-company STC (Standard Telephones & Cables, Ltd.; via ITT), see ITT "Fig. XX: Overview of the intertwined history of the Lorenz, ITT, and STC companies in volved with ILS"

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

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

The F.G.R.I.5069 comprises a main beacon transmitter of type T.1345, with the actual radio transmitter equipment installed in a hut. The T.G.R.I.5041 comprised a main beacon transmitter type T.1254, with the equipment installed in a "radio vehicle" trailer. The installation generated 500 watt "aerial power", which presumably refers to radiated power, not transmitter output power. The crystal-controlled operating frequency was in the range of 30.5-40.5 MHz, with standard Lorenz 1150 Hz modulation. The installation consumed 4-5 kW of supply power (220/250 volt, 50 Hz). Power was supplied via a burried cable from the airfield main supply, or by a diesel-electric generator set. A "Type 2" automatic keying device was used with both types of G.R.I. (ref. 235V2). This device comprises two motorized cam discs. The "interval cam disc" interrupted the normal beacon keying every 1, 2½, or 5 minutes for a period of 5 sec max. During this interval, the "code cam disc" keyed the 2-letter Morse code beacon identification, with 1/6 sec dot-length. During ID transmission, both reflectors of the antenna system were disabled, so as to obtain an omni-directional radiation pattern. There was a possible option to operate the main beacon with either E/T keying (dot/dash, Lorenz standard 1/8 sec and 7/8 sec respectively), or A/N keying. The T.1345 and T.1254 superseded the type T.1122 (ref. 235V5). All transmitter types include the associated antennas, cables, etc. A remote control unit and a monitoring arrangement was located in the airfield's control room. It provided switching devices, transmitter status indication, and control of obstruction lights. Associated aircraft receivers are the R.1124A and R.1125A (ref. 235V3, 235V4).


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

(source: adapted from ref. 235V1)

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

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


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

(source: adapted from ref. 235V1)

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

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


under construction

Time frame?

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

  • Localizer:
  • AN/MRN-1 (introduced mid 1942): VHF (108.3-110.3 MHz, 25 W), Basic Component BC-751 localizer transmitter (w BC-752 90/150 Hz modulators & RF bridge) + monitors (BC-753 (fixed) or BC-754 (portable) course detector + BC-755 filed intensity meter + BC-777 indicator alarm; range 40/70/100 miles at 2500/6000/10000 ft altitude; 5 Alford loop antennas (LP-24, DF Loop for RC-107 & RC-109 U/W MC-528 & MP-79-A) in same horizontal plane; replaces SCR-241;  installed in a K-53 truck.
  • AN/CRN-3 (same, but without truck = fixed), transportable, radio equipment in a tent.
  • AN/CRN-10 (same, with radio equipment on small "V6" (?) trailer and antenna array on simple support structure.#
  • Vs. version with 5/6/7 antennas; with/without anti back-course reflector MC-528, antenna reflector (comprising 2 reflector screens: Z-2004, Z-2005), [optional] part of antenna equipment RC-109 (Loop LP-24-A, Mast MA-5-A, mounting base MP-79-A, various cables)).
  • Aircraft receiver: RC-103. Cross-pointer indicator: I-101.
  • Note: modern day Localizer antenna systems may comprise as much as 32 antennes (typ. 7-element Yagi antennas), spanning 48 m.
  • Glide path:
  • AN/MRN-2: "portable" UHF (5 MHz segment within the 100-156 MHz range), 2-course aural Radio Range NOT GS!!! (100 W carrier + 50 W side-band; 25 W "cone-of-silence" fill-in), with station ID and periodic quadrant ID, simultaneous phone transmission.
  • AN/CRN-2: Glide Path transmitter, double beam modulated CW (MCW). UHF (330-340 MHz (335 MHz preset), 25 W CW). Glide path angle: 2.5°. Range: 15 miles at 3000 ft. Superseded by SCR-592 in Feb 1944.
  • Aircraft receiver set: AN/ARN-5. Similar to AN/CRN-5 set.
  • Marker beacons and Compass Locator Marker
  • AN/MRN-3: mobile (jeep mounted transmitter RC-115 / BC-902-B) marker beacon with 1 horizontal dipole, vertical fan-shaped pattern. VHF (75 MHz, 1 W, CW/MCW); replaces BC-302.
  • Three sets: Outer/Middle/Inner marker, located inside airfield boundary / ca. 1 mile & 4.5 miles from RWY approach end, respectively.
  • Aircraft radio equipment: RC-39, RC-43, RC-193, RC193Z, AN/ARN-8, AN/ARN-12. TBC.
  • Compass Locator: ?
  • Local ground comm.
  • SCR-610, 20 W, FM, 27-38.9 MHz (2 xtal-controlled channels out of 120 possible Xtals), battery powered, range 5 miles.

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

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

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


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

(source: adapted from ref. 230U2)


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

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


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

(source: adapted from ref. 230U2)


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

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


Fig. XX: AN/CRN-2 - Close-up of the upper and lower antenna

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


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

(source: adapted from ref. 251W)

The above figure shows importance of always approaching a glideslope beam from below, so as not to intercept the upper "false" glideslope. Modern-day glide slopes have an angle of 2.5°-3.5°, 3° being the standard.


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

(source: adapted from ref. 251W)

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

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

flight training simulators

Fig. XX: Rougerie's "ground trainer" - ca. 1928, (right) in action at Farman's "blind flying school" at Toussus-le-Noble aerodrome

(source: (left) wikipedia.org, (right) adapted from ref. 235P49)

flight training simulators

Fig. XX: A WW2 RAF Link Trainer poster, and my own 1971 "flight" in a Link Trainer

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

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

Although the Navy didn't purchase the system, WIT officials created the Air-Track Corporation of College Park to sell the landing equipment to commercial airports. Pittsburgh, PA, officials bought and installed the system leading to the first blind landing [using only radio signals for guidance ?? In US or worldwide?] of a passenger-carrying flight on January 28, 1938. Unfortunately, pilots never trusted the system enough to encourage airlines and airports to invest in this system. Ref. 235P2, 235P10.

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

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

MIT Ground Controlled Aproach (GCA) - dead end?

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

ILS instruments

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

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

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

ILS instruments

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

(source: adapted from ref. 235C7)

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

ILS instruments

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

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

ILS instruments

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

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

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

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

Combined instrument

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Outer Marker Middle Marker Inner Marker

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

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

ILS marker beacons

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


Unpaved surfaces that are intended for aircraft operations are composed of unbound or natural materials. This may include gravel, cinders, coral, sand, clay, hard packed soil mixtures, grass, turf or sod. Such surfaces are also referred to as "unimproved".

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

Breguet XIV

Fig. XX: A Breguet XIV (not built by Michelin Co.) on the hard surface taxiway at Aulnat aerodrome

(source photo: www.michelin.com)

The first permanent hard surface runways in the USA were not built until much later - in 1928: at Newark/NJ ("black top" asphalt with cinders, 1600 ft long) and the Ford Motor Co. field at Dearborn/MI (concrete, ref. 229Z23). That same year also in Germany, at Leipzig/Halle airport (400 m concrete).

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

Runways are identifed by a 2-digit number from 01 to 36. So, there is no such thing as, e.g., a Runway 42 - unlike what some stupid movies may suggest. The number is derived by dividing the runway's bearing to Magnetic North by 10, rounded to the nearest integer value. Each runway has two ends, so it actually has two runway numbers - one for each takeoff/landing direction. As runways are straight, these two directions always differ by 180°. So, a runway with a compass direction of 147° is designated Runway 15, and the opposite direction of the same runway is designated 15+18 = 33, combined Runway 15/33. If two or three runways of an airport are parallel (i.e., have the same number), then the letter L, C, or R (for Left, Center, Right) is appended to the runway number, e.g., 27R. With four or five parallel runways, the number of one or two runways is incremented or decremented by one. The earth's magnetic poles move around slowly. So, depending on the latitude of the airport, a runway may have to be re-designated every couple of dozen years.


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

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

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

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


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

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