• On this page:
• [Introduction - Otto Scheller's equi-signal beam system]
• [US Bureau of Standards - "Radio Range" Scheller systems]
• [Yagi-Uda linear phased-array beam antennas]
• [C. Lorenz company / Ernst Kramar - "Scheller" landing beam system]
• [The Lorenz "kicking meter" course deviation indicator system]
• [Mobile Luftwaffe version of the Lorenz landing beam system]
• [Lorenz Co. "Karussel" long-range Luftwaffe beacon system]
• [Marconi and Philips equisignal beam beacons]
• [British landing beam systems based on the Lorenz system"]
• ["US Bureau of Standards & US Army Air Corps - landing beams systems based on Lorenz system]
• [World's first hard-surface runway and taxiways]
• [Patents]
• [References]

• On the "Radio Navigation through WW2" main page:
• [Introduction]
• [Radio direction-finding and radio-navigation terminology]
• [Radio direction-finding]
• [Transmitter technology]

• The other Radio Navigation sub-pages:
• [German stepwise-rotating beam beacons: 1909-1918]
• [British constant-speed rotating beam beacons: 1916-1939]
• [Leader-cable course guidance systems]
• ["Blind" aerial bombing]
• ["Knickebein" - Luftwaffe rotable beam beacon for nav to bombing target]
• [ "X-system" and "Y-system" - Luftwaffe beam beacons for nav to bombing target]
• [Other Luftwaffe rotable/rotating beam beacon systems]
• [Hyperbolic radio navigation systems]
• [Radar systems for navigation: 1904 - 1945]
• [Transponder-based radio navigation systems]

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

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

Latest page updates: June 2022 (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).

INTRODUCTION - THE INGENIOUS EQUISIGNAL BEACON SYSTEM OF OTTO SCHELLER

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.

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.

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.

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:

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.

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)

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.

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)

US BUREAU OF STANDARDS - "RADIO RANGE" SCHELLER 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.

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

(source: German patent 201496 and US patent 2172365)

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

• In US, contrary to Europe, RadNav R&D almost exclusively by various branches of the federal government, instead of private industry.
• US developments reinvented Schellers system, but US Army Air was fully aware of his patents when they took over ca 1926.
• Four-Course Range system, Low-frequency Radio Range (LFR) ; a characteristic of the low-frequency range was the Cone of Silence immediately above the station (cf. 3D radiation pattern in Fig. 62 above).
• Ref. 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]"

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.

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.

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)

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)

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

(source: adapted from ref. 229M)

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.

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)

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

(source: © ipse)

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.

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

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!

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)

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)

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.

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))

YAGI-UDA LINEAR PHASED-ARRAY BEAM-ANTENNA

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.

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.

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°.

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.

C. LORENZ CO. / ERNST KRAMAR - "SCHELLER" LANDING BEAM SYSTEM

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.

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

(source: adapted from ref. 2)

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

(source: ref. 2)

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.

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.

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.

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)

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.

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))

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))

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

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).

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

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

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)

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.

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“

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)

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

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

Fig. XX: 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).

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))

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

(source: ref. 229P2)

THE LORENZ "KICKING METER" COURSE DEVIATION INDICATOR SYSTEM

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

This conversion is done in several stages, see the next Figure. First, a transformer electrically isolates the actual conversion circuitry from the potentially high voltage at the audio output of the receiver. At the same time, this transformer prevents the low impedance of the next converter stage from overloading the receiver's output. Next, a bridge of four solid-state diodes rectifies the tone pulses. The amplitude of the resulting DC-pulses toggles between two levels. These levels correspond to the relative strength of the interlocked tone pulses. If both pulses are equally strong, the rectifier output is a constant DC voltage, equivalent to the strength of the received equisignal. A capacitor is used to smoothen the audio ripple on the DC pulses. The inductance of a second transformer is used to differentiate the DC pulses: a rising edge results in positive induction pulse, a falling edge in a negative induction pulse. These pulses exponentially decay to zero. Two diodes in anti-parallel configuration are used to limit the amplitude of the induction pulses, so they do not reach a level that would damage the downstream meter. The limited induction pulses are fed to a moving-coil meter. A "zero-center" meter is used, so as to be able to indicate both pulses with positive and 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.

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.

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.

THE MOBILE LUFTWAFFE VERSION OF THE LORENZ LANDING BEAM SYSTEM

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".

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.

THE LORENZ "KARUSSEL" LONG-RANGE NAVIGATION BEACON 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.

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.

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)

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.

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.

MARCONI AND PHILIPS EQUISIGNAL BEAM BEACONS

LW/MW "Marconi" range in Australia.

LW/SW Philips equsignal beam beacons

BRITISH LANDING BEAM SYSTEMS BASED ON THE LORENZ SYSTEM

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).

BUREAU OF STANDARDS & US ARMY SIGNAL CORPS - LANDING BEAM SYSTEMS BASED ON THE LORENZ SYSTEM

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.

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)

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?

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.

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.

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)

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.

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.

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)

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

WORLD'S FIRST HARD-SURFACE RUNWAY AND TAXIWAYS

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.

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.

PATENTS

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

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

REFERENCES

• Ref. 1: "Bernhard and Bernhardine", p. 24 in "Some historical and technical aspects of radio navigation, in Germany, over the period 1907 to 1945", Arthur O. Bauer, 28 pp. Source: www.cdvandt.org.
• Ref. 2: pages from the renowned books and other documents by Fritz Trenkle
• Ref. 2A: "Die deutschen Funkführungsverfahren bis 1945" ["The German radio guidance systems through 1945"], Fritz Trenkle, Dr. Alfred Hüthig Verlag, 1987, ISBN 3778516477, 236 pp.
• Ref. 2A1: p. 149 (X-Uhr / X-system clock).
• Ref. 2A2: pp. 76-110, 224.
• Ref. 2B: pp. 62, 94-102 in "Die deutschen Funk-Navigations- und Funk-Führungsverfahren bis 1945" ["The German radio navigation & guidance procedures through 1945"], Fritz Trenkle, Motorbuch Verlag, 1995, 208 pp., ISBN-10: 3879436150.
• Ref. 2C: "Bordfunkgeräte - vom Funkensender zum Bordradar" ["On board radio equipment - from spark transmitter to radar"], Fritz Trenkle, Bernard und Graefe Verlag (publ.), 1986, 283 pp., ISBN 3-7637-5289-7. [table of contents]
• Ref. 2C1: p. 61-63 - "Kommandoübertragungszusätze" ["Command uplink accessories"].
• Ref. 2C2: p. 83-95 - "Eigenpeil- und Zielflug-Verfahren - LW-MW-Peil und Zielfluggeräte" ["RDF and reverse-RDF systems - LW/MW RDF & approach equipment"]
• Ref. 2C3: pp. 97-118 - "Leitstrahl-Verfahren" ["Guidance-beam systems"].
• Ref. 2C4: p. 108 - photo "Große Knickebein Anlage bei Kleve", ["Large Knickebein installation near Cleves"; note: incorrectly identified by Trenkle as station K4 at Kleve, instead of K2 at Bredstedt].
• Ref. 2C5: pp. 119-133 - "Drehfunkfeuer-Verfahren - LW, KW, UKW, DMW, bis 1945" ["Rotating-beam beacon systems, Longwave"].
• Ref. 2C6: pp. 134-140 - "Hyperbel-Navigations-Verfahren" ["Hyperbolic navigation systems"]
• Ref. 2C7: pp. 141-150 - "Entfernungsmeß-Verfahren" ["Distance measuring systems"]
• Ref. 2C8: pp. 198-200 - "Kenngeräte (Bord-Transponder)" [FuG 25 "Zwilling", FuG25a "Erstling"]
• Ref. 2D: "Versuch einer Zusammenstellung deutscher Funkgeräte 1939 ... 1945 LUFTWAFFE / HEER / MARINE (ca .1200 Geräte)" ["Attempt at a compilation of German radio equipment 1939 ... 1945 Air Force / Army / Navy (ca. 1200 equipment items)"], Wolfgang "Fritz" Trenkle, Issue VI.60 (1960), 100 pp. [file size: 38 MB]. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL 2-V/211, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 3: "Most probable position: A history of aerial navigation to 1941" [from hot air balloon to USA entry into WW2], Monte Duane Wright, University Press of Kansas (publ.), 1972, 280 pp.
• Book review by R.V. Jones, in "Journal of Navigation", Vol. 27, Iss. 4 , October 1974 , pp. 542-543. Source: en.booksc.org, accessed November 2021. [pdf]
• Book review by Gerald E. Wheeler, in "Military Affairs", Vol. 39, Nr. 1, February 1975, p. 43. Source: en.booksc.org, accessed November 2021. [pdf]
• Ref. 5: "Instruments of Darkness: The History of Electronic Warfare, 1939-1945", new ed., Alfred Price, Greenhill Books, 2005, 272 pp., ISBN-10: 1853676160; original edition: William Kimber and Co., Ltd, 1967. See note 1
• Ref. 5A: pp. 236-237; Same as pp. 274-275 in the excellent German translation: "Herrschaft über die Nacht: Spionen jagen Radar", Alfred Price, publ.: Bertelsmann Sachbuchverlag Reinhard Mohn, 1968, 304 pp., ASIN B0000BT35X.
• Ref. 5B: p. 82 - second of sixteen photo pages.
• Ref. 6: Transcribed reports from the British Air Ministry, Assistant Director of Intelligence (Prisoner Interrogation),  A.D.I. (K) (a.k.a. "Felkin Reports", after their author). Source: The National Archives of the UK, ref. AIR40/2875 and 2876. Retrieved from www.cdvandt.org.
• Ref. 6A: §19-23 in "Some further notes on G.A.F. Pathfinder procedure" ["EGON" procedure, new EGON procedure, Berhardiner Gerät, Erika Gerät, Y-gerät, "X" Clock, Knickebein jamming],  S.D. Felkin, A.D.I.(K) Report No. 187/1944, 25 April 1944, 5 pp.
• Ref. 6B: §57-59 in "G.A.F. night fighters - R.A.F. Bomber Command countermeasures and their influence on German night fighter tactics" [transcript], S.D. Felkin, A.D.I.(K) Report No. 599/1944, 2 November 1944, 16 pp.
• Ref. 6C: "G.A.F. Night Fighters - Recent Developments in German Night Fighting",  S.D. Felkin, A.D.I. (K) Report No. 125/1945, January 1945, 18 pp.
• Ref. 6D: "The GAF (German Air Force) Signals Organisation in the War" [incl. X-System, X-beam, Knickebein, Y-System (Benito), Zyklop/Cyclop, Erika, Sonne beacons in Spain, radar, FuG25/25A, IFF, Panorama, Centimetre Wave R&D, Egon, Gee, H2S, Berlin-Gerät, Kammhuber night fighting, Window, Wilde Sau, HS293], Samuel Denys Felkin, A.D.I.(K) Report No. 334/1945, 1 July 1945, 27 pp.
• Ref. 6E: "Equipment of a Y-Site" [Berta I, Berta II, S16B, Sadir 80/100, Heinrich I (Peiler, D/F), Heinrich III, FuG 16ZE, FuG16ZY], S.D. Felkin, A.D.I.(K) Report No. 527B/1944, 25 Sept 1944, 13 pp.
• Ref. 6F: "Radio and Radar Equipment in the Luftwaffe- I. Blind Landing and Airborne Communications Equipment" [report of interrogations of General Martini and other PoW's; topics: LFF, JLFF, Fu Bl 2, AWG 1, FuG 10 P, FuGe 16, FuGe 17, FuGe 18, FuGe 15, FuGe 24, FuGe 29], S.D. Felkin, A.D.I.(K) Report No. 343/1945, 1 July 1945, 6 pp.
• Ref. 6G: "Radio and radar equipment in the Luftwaffe - II: Navigational aids" [D/F loop equipment, PeGe 6, FuG 141, FuG 142, FuG145; homing beacons: Schwanboje, Biene; beam systems: Zyklop, Sonne, Mond, Stern, Dora, Komet, Erika, Bernhardine, Hermine; Pulse systems: Ingolstadt, Truhe, Baldur, Baldur-Truhe, Baldur-Bernhardine; Ground control systems: Benito = "Y", Egon, Nachtlicht, Nachtfee, Barbara, Barbarossa, Rübezahl], S.D. Felkin, A.D.I. (K) Report No. 357/1945, 25 April 1944, 18 pp.
• Ref. 6H: "Radio and radar equipment in the Luftwaffe - III: Electric altimeters" [FuG 101A, FuG 102, FuG 103, FuG 104], S.D. Felkin, A.D.I. (K) Report No. 362/1945, 27 July 1945, 3 pp.
• Ref. 6J: "Fighter defence of Germany - Control of fighters by the "Y" Procedure", Samuel Denys Felkin, A.D.I.(K) Report No. 525/1944.
• Ref. 6K: "German knowledge of 'OBOE'", [transcript], S.D. Felkin, A.D.I. (K) Report No. 318/1944, 29 Juni 1944, 11 pp.
• Ref. 6L: "Further Report on the Crew of the Ju.88 8-3 Z6 + FH of 1/K.G.66) shot down by A.A. 5 miles N.W. of Alost, on 23rd January 1945.(Previous A.D.I.(K) Report No.142/1945)" [incl. special navigation aids: EGON, "Y" procedure, "Y" clock, new "X" procedure = "Y" + EGON, FuG 28, Y-Clock (CRT), FuG 17, FuG 25A, FuG 217, Ju-88], S.D. Felkin, A.D.I. (K) Report No. 175/1945, 19 February 1945.
• Ref. 6M: "A G.A.F. Pathfinder Unit - Further report on Ju.88 S-1, Z6+IN, of 5/K.G.66, brought down in the sea off Brighton on 25th March 1944", Samuel Denys Felkin, A.D.I.(K) Report No. 160/1944 (prev. No. 141/1944).
• Ref. 7: "Beiträge der Firma Siemens zur Flugsicherungstechnik und Luftfahrt-Elektronik in den Jahren 1930 bis 1945 (Teil 1 & 2)", H.J. Zetzmann, in "Frequenz - Zeitschrift für Schwingungs- und Schwachstromtechnik"
• Ref. 7A: Part 1: Vol. 9, Nr. 10, 1955, pp. 351-360.
• Ref. 7B: Part 2 (pp. 387, 388, 392): Vol. 9, Nr. 11, 1955, pp. 386-395.
• Ref. 8: "General Electric funds Hitler", Chapter 3 in "Wall Street and the Rise of Hitler", Antony C. Hutton, G S G & Associates Publ., June 1976 (reprint), 162 pp., ISBN 0945001533.
• Ref. 13: p. 405 and 4.09 in "Japanese Electronics", OPNAV-16-VP101, Photographic Intelligence - Report 1, U.S. Navy Dept., Office of the Chief of Naval Ops., Air Intelligence Group, Div. of Naval Intelligence, Naval Photographic Intelligence Center, January 1945, 166 pp. [file size: 33 MB]
• Ref. 14: summary item 27 in "The German Wartime Electricity Supply - Conditions, Developments, Trends", British Intelligence Objectives Sub-comittee (BIOS), Final Report 342, Item No. 33, 28 selected pages. Source: www.cdvandt.org.
• Ref. 15: "Beschreibung und Betriebsvorschrift für Funk-Navigationsanlage FuG 120" [Description and Operating Manual for Radio-Navigation System FuG 120 "Bernhardine", with 2-channel Hellschreiber radio-navigation printer], Telefunken G.m.b.H., document FN-T-GB Nr. 1932, December 1944, 43 pp. [File size: 66 MB; a good-but-lower resoluton file is here 26 MB]
• Ref. 19: p. 122 in "Die Erprobungstelle Rechlin", Christoph Regel, pp. 60-149 in "Flugerprobungsstellen bis 1945: Johannisthal, Lipezk, Rechlin, Travemünde, Tarnewitz, Peenemünde–West", Heinrich Beauvais, Max Mayer, Bernard & Graefe Verl., 1998, 364 pp., ISBN: 3763761179; Vol. 27 of "Die deutsche Luftfahrt : Buchreihe über die Entwicklungsgeschichte der deutschen Luftfahrttechnik", Theodor Benecke, Deutsches Museum
• Ref. 20: pp. 59-63 of "Richt- und Drehfunkfeuer" ["Directional and rotating radio beacons"; 4-Course, Telefunken Compass, Bernhard, Erika, Komet, ILS/LOC/GS], Chapter 3 of “Leitfaden der Funkortung: Eine systematische Zusammenstellung der Verfahren und Anlagen der Funkortung“ [Guide to radio location: a systematic survey of radio location methods and installations], Vol. 1 of "Lehrbücherei der Funkortung", Walter Stanner, 4^th ed., Deutsche RADAR-Verlagsgesellschaft m.b.H., 1957, 160 pp.
• Ref. 28: "Ernst L. Kramar Pioneer Award 1964", in "IEEE Trans. on Aerospace and Electronic Systems", Vol. 11, Issue 2, AES-2, No. 4, June 1964, pp. 81-85 [pdf]
• Ref. 31: "Das Funk-Blindlandegerät" [Fu Bl I, EBl 1, EBl 2, Fu Bl 2], Werner Thote, in "Radiobote", Vol. 2, Nr. 9, May-June 2007, pp. 20-25. Source: radiobote.at. [pdf]
• Ref. 32: "Beschreibung und Betriebsvorschrift für Funklande-Empfangsanlage Fu Bl 1 Ex" [Description and operating instructions for landing receiver system Fu Bl 1 Ex"], DTA 140, C. Lorenz AG, 1940, 59 pp. Source: www.cockpitinstrumente.de
• Ref. 33: pp. xxxxx in "Confound and Destroy: 100 Group and the bomber support campaign", Martin Streetly, Jane's Publishing, Inc. (publ.), 1978, 379 pp. [pdf, file size 35 MB]. See note 1
• Ref. 35: pp. 8-11, 33 in "The Hut Six Story - Breaking the Enigma Codes", Gordon Welchman, M & M Baldwin Publ., 6^th ed., 2011, 263 pp.
• Ref. 38: documents of the Sub-Committee for the Investigation of German Electronic and Scientific Organisation (SIGESO). Source: www.cdvandt.org.
• Ref. 38A: "Navigational Aids for Bombers" [Knickebein, X, Y, Benito, Erika, Sonne, Zyklop], sheet 3-6 in Section 0.1 of A.L. No. 46 of SIGESO, 12/12/1945, Report Vol. 1, Part 2. 
• Ref. 38B: "The Goldwever System of Navigational Aid for U-Boats", sheet 30 in Section 2.2, A.L. No. 61 of SIGESO,12/2/46.
• Ref. 39: Luftwaffe manuals for ground and on-board landing beam systems element. Source: www.cdvandt.org. Retrieved: January 2018, September 2020.
• Ref. 39A: "Funk-Landegerät Fu Bl I - Geräte-Handbuch, Beschreibung und Betriebsvorschrift", Luftwaffe Druckschrift D. (Luft) T.4065, April 1942, 50 pp.
• Ref. 39B: "UKW-Landefunkfeuer 120 Watt und 500 Watt, Aufbau-Anweisung", Luftwaffe Druckschrift D. (Luft) T.4458, June 1943, 8 pp.
• Ref. 39C: "AS 4 Anflugführungssender 4 - Geräte-Handbuch", Luftwaffe Druckschrift D. (Luft) T.4456, June 1943, 36 pp.
• Ref. 39D: "Ansteuerungs-Sender AS 2 - Geräte-Handbuch, Beschreibung und Wirkungsweise sowie Bedienung und Wartung", Luftwaffe Druckschrift D. (Luft) T.4452, May 1941, 38 pp.
• Ref. 39E: "Antenne AFFA 2- Geräte-Handbuch, Beschreibung und Wirkungsweise sowie Bedienung", Luftwaffe Druckschrift D. (Luft) T.4454, September 1941, 17 pp.
• Ref. 39F: "Beschreibung und Betriebsvorschrift für 5 Watt-Ultrakurzwellen-Einflugzeichensender EZS 2", Luftwaffe Druckschrift D. (Luft) T.4451, February 1941, 30 pp.
• Ref. 39G: "Beschreibung und Betriebsvorschrift für Funkfeuer-Kontrolempfänger EBKS", Luftwaffe Druckschrift D. (Luft) T.4450, February 1941, 17 pp.
• Ref. 39H: "120 Watt UKW Leitstrahlsender AS 3" ["UKW Landefunkfeuer, ortsfest"; non-mobile VHF landing beam beacon], Beschreibung Nr. 75/710, C. Lorenz AG, Berlin-Tempelhof, November 1942.
• Ref. 40: documents about FuG 16 and FuG17
• Ref. 40A: "Die Bordfunkgeräte FuG 16 und FuG 17", pp. 28-49 in "Berühmte Bordfunkgeräte - ein Beitrag zur Geschichte der Elektrotechnik" [FuG10, FuG16, FuG17, FuG25a, FuG101a, ...], H. Sarkowski, Expert Verlag, 1983, 80 pp.
• Ref. 40B: "Bordfunkgerät FuG 16 ZY mit Aufbauvorschrift für Antenne des Zielflug-Senders", Luftwaffe Druckschrift D.(Luft)T.4069, 5 August 1944, 114 pp. Source: cdvandt.org.
• Ref. 40C: "Das Bordfunkgerät FuG17", Heft 205 of "Teil 1 - Gerätebeschreibungen" of Luftwaffe Druckvorschrift L.Dv.702/1, April 1941, 28 pp. Source: cdvandt.org, accessed 23 September 2020.
• Ref. 41: documents about airships (Zeppelins, dirigibles, ...)
• Ref. 41A: "Zeppelins over England", Kenneth Poolman, White Lion Publishers (publ.), 1975, 224 pp. Originally published in 1960 by Evans Brothers Ltd. Source: worldhistory.biz, accessed 27 May 2021. [pdf].
• Ref. 41B: "Funkeinrichtung des Zeppelin-Luftschiffes LZ 129" ["Radio equipment of the Zeppelin airship LZ 129 "Hindenburg"], in "Radio-Amateur", Vol. 13, May 1936, 3 pp. Source: dokufunk.org, retrieved 10 June 2021.
• Ref. 41C: "Die Funkeinrichtung des Zeppelin-Luftschiffes LZ 129" ["Radio equipment of the Zeppelin airship LZ 129 "Hindenburg"], T. Pd., in "Zeitschrift:Pionier : Zeitschrift für die Übermittlungstruppen", Vol. 9, Nr. 5, May 1936, pp. 89-93. Source: e-periodica.ch, retrieved 11 June 2021 -- same as ref. 41B, better legible, but without images.
• Ref. 41D: "Die großen Zeppeline - Die Geschichte des Luftschiffbaus" ["The large Zeppelins - The history of airship construction"; German, British, US American], Peter Kleinheins, Wolfgang Meighörner (ed.), 3^rd ed., Springer (publ.), 2004, 273 pp.  [pdf, file size: 58 MB; lower-res version is here, 10 MB] See note 1
• Ref. 41E: pp. 82-83 in "Funkeinrichtung", chapter 9 in "LZ 129 "Hindenburg" - Das Luftschiff des deutschen Volkes", Werner von Langsdorff, H. Bechhold Verlagsbuchhandlung (publ.), 1936, 96 pp.
• Ref. 77: "History of the German night fighter force, 1917-1945", Gebhard Aders, Jane's Publishing Company, 1^st ed., 1979, 284 pp. [file size 62 MB].  See note 1
• This is the translated and edited version (by A. Vanags-Baginskis and B. Gallagher) of the original German version "Geschichte der deutschen Nachtjagd: 1917-1945", Gebhard Aders, Motorbuch Verlag (publ.),1977, 391 pp.
• Ref. 77A: pp. 96, 182.
• Ref. 77B: pp. 194, 195.
• Ref. 77C: pp. 246, 237.
• Ref. 90:
• Ref. 90A: private message to me in March of 2015 in the Axis History Forum.
• Ref. 90B: pp. 21, 57, 58 in "Stations radar et radio-navigation sur le Mur de l'Atlantique - Spécial Normandie d'Antifer à Granville", Alain Chazette, Bernard Paich, Alain Destouches, Jacques Tomine, Jörg Poweleit, Michaël Svejgaard, Histoire & Fortifications (publ.), 2015, 96 pp
• supplement: "Stations radar et de radio-navigation sur le Mur de l'Atlantique (complement photos)", 32 pp.
• Ref. 90C: p. 161 in "Stations radar et radio-navigation sur le Mur de l'Atlantique - Volume 2 -Spécial Belgique - Nord - Pas-de-Calais - Picardie - Haute-Normandie", Alain Chazette, Bernard Paich, Pierre Nowak, Alain Destouches, Jacques Tomine, Ingrid Paindavoine, Histoire & Fortifications, 2016, 160 pp.
• Ref. 90D: "Drawing of a Funk Sende Anlage Bernard 724/725 bunker", 14-March-2015 thread in Axis History Forum; used with permission
• Ref. 90E: "German Military Symbols", U.S. War Dept., General Staff, Military Intelligence Service, January 1943, 152 pp. (public domain, no ©)
• Ref. 93: pp. 115-117 in "The High-Frequency War - A Survey of German Electronic Development", E.S. Henning, HQ Air Materiel Command (AFMC), Wright Field, Dayton/OH, Summary report No. F-SU-1109-ND, 4 June 1946 (US Gov't, hence no copyright).  [file size: 225 MB; a lower-resolution version is here, 56 MB]
• Ref. 110: articles from "IEE Proceedings Part A "Physical Science, Measurement and Instrumentation, Management and Education Reviews", The Institution of Electrical Engineers (publ.), Vol. 132, Issue 6, October 1985. Source: en.booksc.org, accessed 4 November 2021.
• Ref. 110A: "Editorial - historical radar", E.H. Putley, pp. 325-326, [pdf], See note 1.
• Ref. 110B: "Memories of radar research", J.D. Cockcroft, pp. 327-339, [pdf], See note 1.
• Ref. 110C: "The work of TRE in the invasion of Europe", J.W.S. Pringle, pp. 340-358, [pdf], See note 1.
• Ref. 110D: "ASV: the detection of surface vessels by airborne radar",  R.A. Smith, R. Hanbury-Brown, A.J. Mould, A.G. Ward, B.A. Walker, pp. 359-384, [pdf], See note 1.
• Ref. 110E: "The development of centimetre AI", W.E. Burcham, pp. 385-393, [pdf], See note 1.
• Ref. 110F: "Oboe: history and development", A.H. Reeves, A.H., J.E.N. Hooper, pp. 394-398, [pdf], See note 1.
• Ref. 110G: "H2S and the navigator", E.L. Killip, pp. 399-400, [pdf], See note 1.
• Ref. 110H: "Historical note on H2S", A.C.B. Lovell, pp. 401-403, [pdf], See note 1.
• Ref. 110J: "The new H2Ss", J.B. Smith, pp. 404-410, [pdf], See note 1.
• Ref. 110K: "History of fighter direction", N. Orgel, pp. 411-422, [pdf], See note 1.
• Ref. 110L: "The radio war" [TRE, 80 Signals Wing, 100 Group, Knickebein, X-System, Y-System/Wotan/Benito, Jostle, Ground Grocer, Mandrel, Moonshine, Würzburg], Robert Cockburn, pp. 423-434, [pdf], See note 1.
• Ref. 110M: "The story of IFF (Identification Friend or Foe)", Lord Bowden of Chesterfield, pp. 435-437, [pdf], See note 1.
• Ref. 110N: "Development of radar for the Royal Navy 1935-44", J.D.S. Rawlinson, pp. 441-444, [pdf], See note 1.
• Ref. 137: "Ausstrahlung, Ausbreitung und Aufnahme Elektromagnetischer Wellen" ["Radiation, propagation, and absorption of radio waves"], Ludwig Bergmann, Hans Lassen, Vol. 2 of "Lehrbuch der drahtlosen Nachrichtentechnik" ["Textbook of wireless communication"], Nicolai von Korshenewsky (ed.), Wilhelm T. Runge (ed.), Springer -Verlag (publ.), 1940, 286 pp. Source: libarch.nmu.org, retrieved 18 May 2020. [file size: 22 MB]
• Ref. 137A: "Die Dipolreihe, Dipolgruppe, und Dipolebene" ["The dipole row, dipole array, dipole plane"], pp. 62-73.
• Ref. 137B: "Richtantennen für Leitstrahlanordungen (Funkbaken)" ["Directional antennas for guide-beams (radio beacons)"], p. 97-98 in Chapter II.
• Ref. 151: p. 16, 17, 22 in "Jagdschloß A (Lehrunterlagen) Teil I", 2^nd ed., Lehrschule für Fernmeldetechnik, Detmold, November 1944, 115 pp. Source: www.cdvandt.org
• Ref. 164: documents of the Combined Intelligence Objectives Sub-Committee (CIOS). Source: cdvandt.org.
• Ref. 164A: "Institutes of the Bevollmaechtigter fuer Hochfrequenz-Forschung", CIOS, Item No. 1 & 7, File No. XXXI-37, May 1945, 215 pp.; source: cdvandt.org.
• Ref. 164B: "The I.T.T., Siemens and Robert Bosch Organizations" [incl. Lorenz: Elektra, Sonne, Mond, Knickebein, Erika, Goldwever, Hermine, 6-mast Lorenz Adcock D/F based on British patent, Lorenz Blind Approach/Landing, IFF, radar], CIOS, Item No. 1, 7 & 9 (Radar, Signal Communications, Physical & Optial Instruments and Devices), File No. XXXI-38. Source: cdvandt.org. Retrieved 22 September 2019.
• Ref. 164C: "Report on C. Lorenz A.G." [history, factories, relationship with Philips & Telefunken, Stuttgart UHF radio link (FuG0s, FuG03a), Feuerzauber & Feuermolch Oboe-jammer, FuG200, FuG226/Neuling], CIOS, Item No. 1, File No. XXV-12, 13 pp. Source: cdvandt.org. Retrieved 7-Feb-2020.
• Ref. 164D: "Beacon Transmitters", in "Inspection of Philips Works at Eindhoven", Robert Watson Watt, CIOS Target Number 1/42, CIOS file No. III-1, 23-26 September 1944, 56 pp. Source: cdvandt.org. Retrieved 27 March 2022.
• Ref. 172: copy of item in file AIR 29/284 "Central Interpretation Unit (CIU) Medmenham; Interpretation reports and aerial photos (1943)". Item is in the collection of The National Archives; material with UK Crown Copyright, used in accordance with the Open Government License [pdf].
• Summary of the contents of ref. 172A.
• Ref. 172A: "German “Windjammer” R.D.F. Stations", part of "Monthly interpretation review for July 1943", 7 pp.
• Ref. 173: copy of items in file AIR 14/3577 "Signals investigation on 27 to 35 Mc/s "Windjammer" (1943/1944)". Items are in the collection of The National Archives; material with UK Crown Copyright, used in accordance with the Open Government License [pdf].
• Summary of the contents of ref. 173A-173E.
• Ref. 173A: "Windjammer" observation", by R.A. Fareday (Noise Investigation Bureau [Electronic Intelligence], N.I.B., London), dated 20^th June 1944, 1 page.
• Ref. 173B: "Possible "Windjammer" transmissions", report by Flight Lieutenant Douglas of 192 Sq., dated 16^th December 1943, 1 page.
• Ref. 173C: "192 Squadron Flight report No. 215/43" by F/Lt Robinson to Squadron Leader Burtler, dated 15^th November 1943 (actual report by P/O G.F. Evans of 13^th November 1943), 6 pages.
• Ref. 173D: "Windjammer – Arcachon", letter from Air Ministry A.I.4. [intelligence branch section supervising RAF Y Service] to Commanding Officer of 192 Squadron, dated 16^th July 1943, 1 page + 1 aerial photo.
• Ref. 173E: "The Windjammer and Dreh-Elektra", by 192 Squadron Leader J. Whitehead, dated 18^th June 1943, 1 page.
• Ref. 174: copy of items in file AIR 14/3594 "Windjammer" [ = "Bernhard"] station: photographs and interpretation reports. Includes vertical and low oblique aerial photographs of "Windjammer radar" sites in Germany and France (1943/1944)". Items are in the collection of The National Archives; material with UK Crown Copyright, used in accordance with the Open Government License [pdf].
• Summary of the contents of ref. 174A-174J.
• Ref. 174A: Letter entitled "W/T Bergen/Belvedere" by Squadron Leader C.W. Swanell on behalf of the Group Captain commanding R.A.F. Station Medmenham to R.V. Jones (A.D.I. Science), dated 9^th April 1943, 1 page + 1 photo
• Ref. 174B: Aerial photo of station "Bergen/Belvedere" [The Netherlands], photo No. 3022, taken 22^rd March 1943 by 541 Squadron
• Ref. 174C: Letter entitled "W/T – Bergen/Belvedere" by Group Captain commanding R.A.F. Station Medmenham to R.V. Jones (A.D.I. Science), dated 9^th April 1943, 1 page. (note: photos referenced in letter not on file)
• Ref. 174D: Letter entitled "W/T Desvres/Le Bois Julien" on behalf of Group Captain commanding R.A.F. Station Medmenham to R.V. Jones (A.D.I. Science), dated 15^th November 1942, 1 page + 2 photos.
• Ref. 174E: Letter entitled "W/T: Desvres/Le Bois Julien" on behalf of Group Captain commanding R.A.F. Station Medmenham to R.V. Jones (A.D.I. Science), dated 29^th March 1943, 1 page + 1 photo.
• Ref. 174F: "Interpretation Report No. G. 308" dated 28^th June 1942, of aerial photos taken over Desvres/Le-Bois-Julien at altitude of 20k ft during Sortie A/945 on 20^th June 1942, 1 page + 1 photo.
• Ref. 174G: "Interpretation report No. G.590" dated 6^th October 1942, of aerial photo taken over locality Morlaix, W/T station Mt. St. Michel, at altitude of 12k ft during Sortie Q/21 on 24^th September 1942, 2 pages + 1 photo.
• Ref. 174H: Letter entitled "W/T: Pouzauges/St.Michel-Mont-Mercure" on behalf of Group Captain commanding R.A.F. Station Medmenham to Squadron Leader Whitehead (A.I.4), dated 29^th March 1943, 1 page + 3 photos.
• Ref. 174J: Photos No. 4065 and 4066 of station at St. Vaast / La Pernelle, taken 31^st March 1943 from off shore. [station is fully, though vaguely, visible on horizon]
• Ref. 181: "Drehfunkfeuer System Telefunken - Teil 1: Verfahrensbeschreibung EC1-4262" [Telefunken rotating radio beacon, part 1: description of the method], Adalbert Lohmann, Berlin, October 1942, 129 pp., copy nr. 29, personal copy of Albrecht Leyn [note: this document was never printed, other than a very limited number of personal copies, individually approved by Dept. LC-4 (Technisches Amt) of the RLM; ref. 183]; source: corporate archives of DTM Berlin, part of file nr. I.2.060C-06172  [file size: 62 MB; a lower-resolution version is here, 28 MB]
• Ref. 183: "Das Drehfunkfeuer-Verfahren Bernhard und Bernhardine, System Telefunken" ["Verfahrensbeschreibung Bernhard, Bernhardine", description of the Bernhard-Bernhardine method], Adalbert Lohmann, Telefunken Gesellschaft für drahtlose Telegraphie m.b.H., Berlin-Zehlendorf, Telefunken document EC 1 4310, July 1943, 28 pp., copy nr. 11; source: corporate archives of DTM Berlin, file nr. I.2.060C-04403.
• Ref. 184: radio direction finding
• Ref. 184A: articles on Watson-Watt direction finding method
• Ref. 184A1: "Basics of the Watson-Watt Radio Direction Finding Technique", RDF Products Web Note WN-002, December 1998, 12 pp. Source: www.rdfproducts.com, accessed 3 March 2020. [pdf]
• Ref. 184A2: "Busting Watson Watt DF ambiguity - maths edition", David A Moschella, cyntony.com blog post, 13 July 2017. Accessed 16 March 2020. [pdf]
• Ref. 184A3: "Adcock/Watson-Watt Radio Direction Finding", Ismael Pellejero (EA4FSI) Technical Articles, 15 August 2012. Accessed 3 March 2020. [pdf]
• Ref. 184A4: "Über den Rahmeneffekt eines aus vertikalen Linearantennen bestehenden Adcock-Peilers: Der Zusammenbruch eines Dogmas" ["Loop effect of an Adcock D/F - the collapse of a dogma"; Adcock Watson-Watt configuration does not always eliminate horizontally polarized signals], Gottfried Eckart, pp. 151-178 in "Sitzungsberichte", Verlag der Bayerischen Akademie der Wissenschaften (publ.), 1 January 1972, 28 pp.  [pdf]
• Ref. 184B: "Het radio-peilen" ["Radio D/F"; in Dutch language; DF, multi-path, Telefunken Compass toroidal coil coupling, radio goniometer, rotating loop, fixed-course crossing loop pair, night effect, shoreline effect], Anthonet Hugo de Voogt, pp. 74-94 in "Tijdschrift van het Nederlandsch Radiogenootschap", 23 April 1921. Source: kivi.nl (Deel 01), accessed 18 March 2020.
• Ref. 184C: "Antennas for radio direction finding (RDF)", Chapter 23 (pp. 439-456) in "Practical Antenna handbook", 4^th ed., Joseph J. Carr, McGraw-Hill, 2001, 625 pp.
• Ref. 184D: "Summary Technical Report", E.C. Jordan et al, Technical Report No. 4, The Radio Direction Finding Research Laboratory, Dept. of Electrical Engineering, University of Illinois, Urbana/IL/USA, 15 April 1948, 70 pp. Source: Defense Technical Information Center (DTIC). Accessed 12 March 2020. [pdf] [Summary]
• Ref. 184E: "1957 Pioneer Awards in Aeronautical and Navigational Electronics: Alessandro Artom" [invention of the radio goniometer by Alessandro Artom, i.e., before Bellini & Tosi], Robert I. Colin, pp. 44-47 in "IRE Trans. on Aeronautical and Navigational Electronics", Vol. ANE-4, Issue 2, June 1957 [pdf]
• Ref. 184F: "Sammlung der Vorträge anlässlich der Arbeitstagung "Navigation", Arbeitskreis "Navigation", Bevollmächtigte der Hochfrequenzforschung ["Collection of presentations made at the workshop of the "Navigation" working group of the Commissioner for RF Research"], at Ferdinand Braun Institute, Landsberg am Lech, Germany, 23/24 March 1944. Source: cdvandt.org. Accessed 14 March 2020.
• Ref. 184F1: "Über grundsätzliche Fragen der Richtungs- und Entfernungsmessung" ["About fundamental questions regarding radio direction and distance measurement"], Paul von Handel, pp. 9-26 [pdf]
• Ref. 184F2: "Funknavigation mittels Laufzeitverfahren auf Kurzwelle" ["Short-wave radio navigation by means of time-of-flight method"], W. Dieminger, pp. 54-67. [pdf]
• Ref. 184F3: "Empfangs- und Peilanlagen mit gebündelter Charakteristik (Sektorpeilanlagen)" ["Directional reception and DF installations (sector-DF)"; RDF "Guben", "Wullenwever, "Brommy"], Hermann Janssen, pp. 98-120 in  [pdf]
• Ref. 184G: "Reduction of Night Error in Radio Direction-Finding Equipment for Aerodromes", H. Busignies, in "Electrical Communication - A Journal of Progress in the Telephone, Telegraph and Radio Art", Int'l Standard Electric Corp., Vol. 16, No. 3, January 1938, pp. 213-232. Source: www.worldradiohistory.com, retrieved 22 May 2020.
• Ref. 184H: "Funkortung" ["Radio direction finding"], Wilhelm Tolmé Runge, pp. 7, 8 in "Telefunken Hausmitteilungen", Telefunken, Vol. 20, Nr. 82, December 1939.
• Ref. 184J: "Air Navigation Systems: Chapter 3. The Beginnings of Directional Radio Techniques for Air Navigation, 1910–1940", in "The Journal of Navigation", Vol. 43, Issue 3, September 1990, pp. 313-330. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 184Jbis: comments to ref. 184J - "The Beginnings of Directional Radio Techniques for Air Navigation, 1910–1940" [incl. RAF air navigator RDF rules], F.C. Richardson, in "The Journal of Navigation", Volume 43, Issue 3, September 1990, pp. 441-442. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 184K: "Introduction into Theory of Direction Finding", pp. 62-85 in "Rohde & Schwarz Radiomonitoring & Radiolocation Catalog 2016", 24 pp. Retrieved 28 February 2020.
• Closely related: "An Introduction to Radio Direction Finding Methodologies", Paul Denowski, Rohde & Schwarz, 99 pp. Accessed 3 March 2020. [pdf]
• Ref. 184L: "Drahtloses Peilen" [wireless direction finding], A. Esau, pp. 3-12 in "Telefunken-Zeitung", Vol. IV, Nr. 22, March 1921. [Summary]. Source: radiomuseum.org.
• Ref. 184M: "War secrets in the ether", Wilhelm F. Flicke, translation by Ray W. Pettengill of Flicke's original German manuscript "Kriegsgeheimnisse im Aether", source: US National Security Agency (NSA), retrieved 8 March 2020.
• Part I & II (the period from the inception of the German Radio Intercept Service to the End of WW I, and the period between the two World Wars), NSA Document ID A59421, 288 pp. [pdf]
• Part III (aspects of the large scale espionage and the counterespionage (crypto, radio agents,..)), NSA Document ID A59332, 428 pp. [pdf]
• Ref. 184N: "Geschichte der Funkpeiltechnik" ["History of radio direction finding"], Rudolf Grabau, in "Funkgeschichte" (Mitteilungen der Gesellschaft der Freunde der Geschichte des Funkwesens (GFGF) e.V). [Keywords]
• Ref. 184N1: "(1) - Entwicklung der Funkpeilung bis 1945" [Development up to 1945], Vol. 28, 2005, Nr. 164, pp. 268-276. Source: www.radiomuseum.org, accessed 28 March 2020. Also docplayer.org, accessed 27 May 2021. [pdf]
• Ref. 184N2: "(2) - Entwicklung der Funkpeilung ab 1945" [Development from 1945 on], Vol. 29, 2006, Nr. 165, pp. 24-30. Source: www.radiomuseum.org, accessed 28 March 2020. Also docplayer.org, accessed 27 May 2021. [pdf]
• Ref. 184P: "Radio Direction Finding", US Army Field Manual No. 30-476, 8 April 1977, 221 pp. [file size 25 MB]
• Ref. 184Q: "Direction and Position Finding by Wireless", Ronald Keen, The Wireless Press Ltd. (publ.), 1922, 397 pp. Source: archive.org. Accessed: 6 May 2020. [Keywords: directional reception & transmission, incl. loop, cardioid, propagation]
• Ref. 184R: "Radio direction-finding and navigational aids, some reports on German work issued in 1944-45", Scientific and Industrial Research (D.S.I.R.) Radio Research Board, Special Report No. 21, 1951, 96 pp.
• 1-page review of the above document: "Radio Direction-Finding and Navigational Aids", in "Nature", Vol. 169, Nr. 4308, 24 May 1952, p. 785. Source: nature.com, retrieved 14 October 2020.
• Ref. 184S: articles about the Wullenwever RDF system
• Ref. 184S1: "Beschreibung für Großpeil- und Empfangsanlage Wullenwever Type HF 2076" ["Description of large RDF and receiver installation "Wullenwever" type HF 2076"], 11 March 1946, 27 pp. Source: cdvandt.org. Retrieved 3 February 2020.
• Ref. 184T: "The determination of the direction of arrival of short radio waves", H.T. Friss, C.B. Feldman, W.M. Sharpless, in "Proceedings of the Institute of Radio Engineers", Vol. 22, Nr. 1, January 1934, pp. 47- 78. Source: worldradiohistory.com, retrieved 21 July 2020.
• Ref. 184U: articles in "Electrical Communication - A Journal of Progress in the Telephone, Telegraph and Radio Art", published by "International Standard Electric Corp". Source: worldradiohistory.com, accessed 17 August 2020.
• Ref. 184U1: "The automatic radio compass and its application to aerial navigation", H. Busignies, in Vol. 15, No. 2, October 1936, pp. 157-172.
• Ref. 184U2: "Mountain effects and the Use of Radio Compasses and Radio Beacons for Piloting Aircraft", H. Busignies, in Vol. 19, No. 3, 1941, pp. 44-70.
• Ref. 184U3: "Evaluation of Night Errors in Aircraft Direction Finding, 150-1500 Kilocycles", H. Busignies, in Vol. 23, No. 1, March 1946, pp. 42-62.
• Ref. 184V: "Funkpeilung als alliierte Waffe gegen deutsche U-Boote 1939 - 1945: Wie Schwächen und Versäumnisse bei der Funkführung der U-Boote zum Ausgang der "Schlacht im Atlantik" beigetragen haben" [file size 74 MB], Arthur O. Bauer, Ralph Erskine, Klaus Herold, Liebich Funk GmbH (publ.), 1997, 323 pp., ISBN 3-00-002142-6. Source: cdvandt.org, retrieved 28 September 2020.
• An excerpt in English is: "HF/DF An Allied Weapon against German U-Boats 1939-1945", Arthur O. Bauer, 1998, 23 pp. Source: cdvandt.org, retrieved 28 September 2020.
• Ref. 184W: "Radio Direction Finding, 10 kc/s to 550 kc/s", Walter C. Weaver, MsEE Thesis, U.S. Naval Postgraduate School, 1957, 107 pp. Source: archive.org, retrieved 14 October 2020.
• Ref. 184X: "Direction finder and antenna research" [file size 38 MB; full resolution file is here, 242 MB], Office of Scientific Research and Development, National Defense Research Committee, Division 13 (Electrical Communication), Summary Technical Report, 1946 (declassified 1960), 292 pp. Source: loc.gov, retrieved 19 February 2021.
• Ref. 184Y: "Methods of radio direction finding as an aid to navigation: the relative advantages of locating the direction finder on shore and on shipboard", F.W. Dunmore, Dept. of Commerce, Bureau of Standards, Letter Circular No. 56 (LCIRC 56), 27 March 1922, 18 pp. Source: nist.gov, retrieved 13 April 2021.
• Ref. 184Z: "Wireless Direction Finding", C.B. Carr, in "Aircraft Engineering and Aerospace Technology", Vol. 2, Iss. 12, December 1930, pp.305-307. Source: en.booksc.org, accessed April 2021. [pdf, See note 1].
• Ref. 185: radio location & navigation, general articles, articles covering multiple systems, airways, airmail
• Ref. 185A: "Survey of Radio Navigational Aids" [DF, Shoran, Oboe, DME, transponders, radar, Loran, GEE, Decca, Raydist, Micro-H, Consol, Sonne, Navaglobe, A-N ranges, CAA Omnirange, ILS landing beam, radio altimeters, rotating beacons, Orfordness range, Navar, Teleran, Navascope], Robert I. Colin, in "Electrical Communication" (Technical Journal of the International Telephone & Telegraph Corporation and Associate Companies), Vol. 24, No. 2, June 1947, pp. 219-261. Source: www.worldradiohistory.com; accessed 27 March 2020.
• Ref. 185B: "The Geography of Radionavigation and the Politics of Intangible Artifacts", William Rankin, in "Technology and Culture", Volume 55, Number 3, July 2014, pp. 622-674 [pdf]
• Ref. 185C: "Electronic Navigation Systems", Summary Technical Report of Division 13 (Electrical Communication) of the National Defense Research Committee (NDRC) - Vol. 2B, 1946, 374 pp. [file size 211 MB; a lower-but-good resolution version is here, 48 MB]. Source: US Library of Congress  www.loc.gov. Retrieved 8 August 2018. [Beacons & interrogators, Oboe, Shoran, Micro-H, DME, Gee, Loran, Decca, POPI, A-N Radio Range, ADF & homing,  Sonne/Consol (AN/FRN-5), Bendix automatic position plotter, CAA VHF Omni beacon, CAA LF Omni beacon, Federal Long-Range Navigation System, airborne radar, search radar as navigational aid, short-range approach system (AN/APN-34), radar (ground) mapping, ground-position indicator (GPI, AN/APA-44), Sperry Omni Range & Distance Indicator, RCA television radar system, miscellaneous German navigational systems, comparison table]
• Ref. 185C1: "Miscellaneous enemy navigational systems" [Elektra (Electra), X-System (Benito), Knickebein, (Ruffian), Hermine, Egon, Rübezahl, Bernhard/Bernhardine, Hyperbel (Hyperbol), Truhe, Zyklop (Cyclop), Dora, Erika, Diskus, Schwanboje, Nachtfee], section 30, 6 pp.
• Ref. 185C2: "Sonne (Consol)", section 17, 26 pp.
• Ref. 185C3: "A-N Radio Range" [incl. Four-course Aural Range], Section 15, 6 pp.
• Ref. 185D: "Air Navigation", U.S. Navy Hydrographic Office H.O. Publication No. 216, corrected print 1963, 717 pp.
• Ref. 185D1: "Lines of Position, Bearings, and Fixes", Chapter IX, pp. 188-202
• Ref. 185D2: "Low Frequency Radio Range", pp. 288-300 in Chapter XI "Radio" (pp. 261-300).
• Ref. 185D3: "Hyperbolic Navigation Systems" [Loran, Decca, Lorac, Sofar, Consol, Sonne, Consolan, GEE], Chapter XIII, pp. 345-365.
• Ref. 185E: "On the origins of RF-based location", Hans Gregory Schantz, in "Proc. 2011 IEEE Radio & Wireless Symposium", Phoenix/AZ/USA 16-20 Jan., 2011. Source: researchgate.net, retrieved 16 Jan 2020.
• Ref. 185F: "Radiobeacons and radiobeacon navigation", George R. Putnam, U.S. Dept. of Commerce, Lighthouse Service, 1 July 1931, 44 pp. [pdf]
• Ref. 185G: p. 260 in "A survey of continuous-wave short-distance navigation and landing aids for aircraft", Caradoc Williams, in "Journal of the Institution of Electrical Engineers - Part IIIA: Radiocommunication", Volume 94, Issue 11, March-April 1947, pp. 255 - 266.
• Ref. 185H: "History of radio flight navigation systems - Memoirs of Dr. E. Kramar", M. Hollmann & P. Aichner (translation, ed.), 15 pp. Source: radarworld.org. [Scheller A/N, Lorenz E/T, Telefunken Knickebein, Hermine, X-System / Wotan I, Four-Course Range, ILS, Elektra, Consol, Erika, Komet, Hohentwiel]
• Ref. 185J: magazine and journal articles in German
• Ref. 185J1: "Navigation und Luftsicherung" ["Navigation and air traffic control"], Leo Brandt, pp. 25-80 in "Arbeitsgemeinschaft für Forschung des Landes Nordrhein-Westfalen", Vol. 13, Springer Fachmedien, 1952, 98 pp. Accessed 3 March 2020. [pdf]
• Ref. 185J2: "Die Funknavigation der Luftfahrt", August Leib, in "Telefunken Hausmitteilungen", Telefunken, Vol. 20, Nr. 82, December 1939, pp. 9-68.
• Ref. 185J3: "Flugsicherung durch Richtfunkbaken" ["Radio-beacon aids to aerial navigation"], H. Rahskopff, in "Zeitschrift des Vereins deutscher Ingenieure (V.D.I.)", Vol. 75, 4 January 1931, pp. 116-117.
• Ref. 185J4: "Neuzeitliche Funknavigation - 1. Teil" ["Modern radio navigation, part 1"], W.R. Schulz,  in "Funk-Technik" (FT), "Zeitschr. für das gesamte Elektro-Radio und Musikwarenfach" (1946-49), "Fachzeitschr. für die Elektro- und Radiowirtschaft" (starting 1950), No. 8, April 1948, pp. 190-191.
• Ref. 185J5: "Neuzeitliche Funknavigation - 2. Teil" ["Modern radio navigation, part 2"], W.R. Schulz, in "Funk-Technik", No. 9, May 1948, pp. 216-217. Source: nvhrbiblio.nl, retrieved March 2021.
• Ref. 185J6: "Neuzeitliche Funknavigation - 3. Teil" ["Modern radio navigation, part 3"], W.R. Schulz, in "Funk-Technik", No. 10, May 1948, pp. 242-243. Source: nvhrbiblio.nl, retrieved May 2021.
• Ref. 185J7: "Funkbaken" ["Radio beacons"; A/N Radio Range, SBA, BABS, Eureka, Rebecca, Z, Navaglobe, VOR, ILS] W.R. Schulz, in "Funk-Technik", Nr. 1, January 1950, pp. 10, 11. Source: nvhrbiblio.nl, retrieved March 2021.
• Ref. 185K:
• Ref. 185K1: "Radio in navigation" [Part 1], C.D. Tuska, in "Journal of the Franklin Institute", Vol. 228, Iss. 4, October 1939, pp. 433-443. Source: en.booksc.org, retrieved 20 April 2021 [pdf, See note 1]
• Ref. 185K2: "Radio in navigation" [Part 2], C.D. Tuska, in "Journal of the Franklin Institute", Vol. 228, Iss. 5, November 1939, pp. 581-603. Source: en.booksc.org, retrieved 20 April 2021 [pdf, See note 1]
• Ref. 185L: "A Brief Description of the Major Second World War Navigational Aids", Brian Kendal, in "Journal of Navigation", Vol. 45, No 1, Januay 1992, pp. 70 - 79. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 185M: "Highlights of antenna history", Jack Ramsay, in "IEEE Communications Magazine", Vol. 19, Iss. 5, September 1981, pp. 4-16. Accessed 6 May 2020. [pdf]
• Ref. 185N: "A review of radio aids in aviation" [DF, Radio Ranges, homing, hyperbolic, Gee, Loran, Decca, Lorenz BAS, VHF/UHF ILS], C.B. Bovill, in "The Journal of the British Institution of Radio Engineers", Vol. VI, Nr. 6, December 1946, pp. 250-272. Source: delibra.bg.polsl.pl, retrieved 20 April 2021.
• Ref. 185P: "Radio navigation in the 1920s" [abstract], C. Powell, in "Journal of the Institution of Electronic and Radio Engineers (IERE)", Vol. 56, Nr. 8-9, August/September 1986, pp. 293-297. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 185Q: "La Radionavigation" [in French], J. Piergo, pp. 159-167 in "Science et Vie", No. 349, October 1946.
• Ref. 185R: "The Aeronautical Navigational Radio Service" [Keywords: Consol, Decca, Loran, GEE, SBA, BABS, MF Range], Chapter VII (pp. 101-109) in "The Civil Aviation Communications Handbook", Vol. 5 of CAP series (M.C.A.P.5), Great Britain Ministry of Civil Aviation, 2^nd ed., 1949, 286 pp. Source: atchistory.files.wp.com. Accessed 19 May 2020. [pdf, file size 26 MB]
• Ref. 185S: "RF Positioning - Fundamentals, Applications, and Tools" [Keywords: RDF, TFK Kompass, Orefordness, Sonne, Gee, Oboe, Gee-H, Loran], Rafael Saraiva Campos, Lisandro Lovisolo, Artech House (publ.), 29 pp. Accessed: 31 January 2020. [pdf]
• Ref. 185T: articles about airmail and airlines
• Ref. 185T1: "Mail Planes Radio Equipment", in "Radio Topics", March 1924, pp. 15-16. Source: worldradiohistory.org, accessed 14 April 2020.
• Ref. 185T2: "Airlines and Air Mail - The Post Office and the birth of the commercial aviation industry", F. Robert van der Linden, The University Press of Kentucky, 2002, 367 pp. Source: core.ac.uk, retrieved 12 February 2021 [file size: 25 MB]
• Ref. 185T3: "Airmail: A Brief History", United States Postal Service, March 2018, 7 pp. Source: usps.com, retrieved 21 October 2020.
• Ref. 185U: "A radio-acoustic method of locating positions at sea: Application to navigation and to hydrographical survey", A.B. Wood, H.E. Browne, in "Proc. of the Physical Society of London", Vol. 35, Part ???, No. 1, 15 April 1923, pp. 183-193. Source: en.booksc.org, accessed 27 May 2021. [pdf, See note 1]
• Ref. 185V: "Aerodrome and Air Route Control", in "The Marconi Review", No. 65, March-April 1937, pp. 9-19. Source: worldradiohistory.com, retrieved 20 April 2021.
• Ref. 185W: "Navigation by cigars" [orig. published in a Pittsburgh newspaper on 19 May, 1938], on p. 47 in "A Place in the Sky: A History of the Arnold Palmer Regional Airport, 1919-2001", Richard David Wissolik (gen. ed.), Saint Vincent College for Northern Appalachian Studies (publ.), 2001, ISBN-13: 978-1885851178, 225 pp.
• Ref. 185X: publications about aviation/flight navigation in general
• Ref. 185X1: "Flight Navigator Handbook", US Dept. of Transportation, Federal Aviation Administration, publication FAA-H-8083-18, 2011, 281 pp.
• Ref. 185Y: articles  in "The Journal of Navigation"
• Ref. 185Y1: "Air Navigation Systems: Chapter I. Astronomical Navigation in the Air 1919–1969", J.E.D. Williams, in "The Journal of Navigation", Vol. 41 , Issue 3, September 1988, pp. 375-406. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 185Y2: "Air Navigation Systems: Chapter I. Astronomical Navigation in the Air 1919–1969. Part II - Instruments", J.E.D. Williams, in "The Journal of Navigation", Vol. 42 , Issue 1, January 1989, pp. 73-91. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 185Y3A: "The beginnings of air radio navigation and communication", Brian Kendal, in "The Journal of Navigation", Vol. 64, Iss. 1, January 2011, pp. 157-167.. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]]
• Ref. 185Y4B: response to ref. 185Y3A - "The beginnings of air radio navigation and communication", Walter Blanchard, in "The Journal of Navigation", Vol. 64, Iss. 3, July 2011, pp. 571-572. Source: en.booksc.org, accessed 27 May 2021. [pdf, See note 1]
• Ref. 185Z: articles by Robert Watson-Watt
• Ref. 185Z1: "Radio Aids to Navigation", Robert Watson-Watt, in "The Journal of Navigation", Vol. 1, Iss. 1, January 1948, pp. 15-21. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 185Z2: "The evolution of radiolocation" [incl. Oboe, Rebecca-Eureka, Orefordness, G-H, BABS], Robert Watson-Watt, in "Journal of the Institution of Electrical Engineers - Part I: General", Vol. 93, Iss. 69, September 1946, pp. 374-382 Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 186: Transmitter technology - spark gap, arc converter, machine generator, vacuum tube (incl. micro wave)
• Ref. 186A: pp. 420-423 in "Handbuch der drahtlosen Telegraphie und Telephonie - Ein Lehr- und Nachschlagebuch der drahtlosen Nachrichtenübermittlung" ["Handbook of wireless telegraphy and telephony - a textbook and reference book of wireless communication"] , Vol. 1, Eugen Nesper, Julius Springer (publ.), 1921, 708 pp. Source: archive.org, accessed 30 March 2020. [pdf; file size: 65 MB]
• Ref. 186B: "Die »Tönenden Funken« - Geschichte eines frühen, drahtlosen Kommunikationssystems, 1905-1914" ["Tonal quenched spark gap transmission - history of an early wireless communication system"], Michael Friedewald, Vol. 2 of "Aachener Beiträge zur Wissenschafts- und Technikgeschichte des 20. Jahrhunderts", Verlag für Geschichte der Naturwissenschaften und der Technik (GNT-Verlag, publ.), 1999, 185 pp., ISBN 978-3-928186-38-4. [Table of contents and review]
• Ref. 186C: "Über die Intensität der beiden Schwingungen eines gekoppelten Senders" ["About the intensity of both types of oscillations of a coupled transmitter"; quenched-spark transmitter], Max Wien, in "Physikalische zeitschrift", Vol. 7, Nr. 23, 15 November 1906, pp. 871-872.
• Ref. 186D: "Beschreibung der kommerziellen Land-Schiff-Station Telefunken Type 0,5 T.K. 0,5 KW Antennen-Schwingungsenergie bei 1,5 KW Primärenergie" ["Description of the Telefunken commercial land/ship-board transmitter model 0,5 T.K. 0.5 kW output power for 1.5 kW dissipation"], 1916 Telefunken brochure (transcribed and adapted by Heinrich Busch, 2016). Source: seefunknetz.de, accessed 3 April 2020. [pdf]
• Ref. 186E: "The Spark Transmitter", "Section "A", 27 pp, in "Wireless telegraphy Theory", Vol. II of "Admiralty Handbook of Wireless Telegraphy", H.M. Signal School, 1938, 1943 revised ed. , B.R.230, 530 pp. Accessed 15 April 2019. [pdf]
• Ref. 186F: "Die technische Entwicklung der Verschiedenen F.T.-Systeme" ["The technical development of various spark transmitter systems"; Poulsen, Wien, HF machine-generators], pp. 3-6 in "Funkentelegraphie für Flugzeuge" [Spark gap telegraphy for aircraft], Erich Niemann, Vol. IX of "Handbuch der Flugzeugkunde", Richard Carl Schmidt & Co. (publ.), 1921, 434 pp. Source: archive.org, accessed 15 April 2020. [pdf]
• Ref. 186G: "Wireless telegraphy", Jonathan Zenneck, McGraw-Hill Book Co. (publ.), 5^th ed., 1918, 443 pp. [pdf; file size: 360 MB]; translation of the German original "Lehrbuch der drahtlosen Telegraphie", Jonathan Zenneck, F. Enke (publ.), 1913, 521 pp.
• Ref. 186G1: Chapter VII: "Transmitters of damped oscillation" [Marconi, Braun, Wien, stationary & rotating electrodes, quenched], pp. 173-212. [file size: 35 MB]
• Ref. 186G2: Chapter VIII: "High frequency machines for undamped oscillations" [Fessenden, Alexanderson, C. Lorenz Co., Goldschmidt, Eberswalde], pp. 213-219.
• Ref. 186G3: Chapter IX: "Undamped oscillations by the arc method" [Poulsen], pp. 220-245. [file size: 21 MB]
• Ref. 186G4: §207 "The advantages of directive signalling" [incl. Telefunken Compass], pp. 365-370.
• Ref. 186H: §8 of Article 5 (pp. 36-37), §1 & §3 of Article 16 (p. 74-76) in International Telegraph Convention 1927 - Treaties, Washington/DC/USA, 1927, 171 pp. Source: International Telecommunication Union, accessed 29 April 2020.
• Ref. 186J: "Zusammenstellung der modernsten tönenden und ungedämpften Radio-Stationen und -Geräte" ["Overview of the most modern quenched spark and undamped (continuous wave) radio sets and equipment"], Telefunken Gesell. für drahtlose Telegraphie m.b.H., product catalog, November 2020 (product status of early 1919), 244 pp. [file size: 32 MB]. Source: www.cdvandt.org. Accessed 1 May 2020.
• Ref. 186J1: Chapter 2, Group II: "Gruppe II. Land- und Schiffs-Stationen" ["Group II, Land and shipstations"], 30 pp. [singing spark transmitter models 0,2 TK; 0,5 TK; Debeg-Schrank-Station; 1,5 TK; 2,5 TK; 5 TK; 7,5 TK; 10 TK; 15 TK; 25 TK; 35 TK; 0,4 TV Behelfs-Station; 0,5 TV; 1 TV; 2 TV; 2,5 TV; 4 TV; 10 TV; all of these spark transmitter models appear to have alreday been marketed by mid-1913; continuous wave vacuum tube transmitter models 0,5 kW; 1 kW, 5 kW].
• Ref. 186J2: Chapter 2, Group III: "Gruppe III. Flugzeug- und Luftschiffstationen" ["Group III, Aeroplane and airship stations"], 16 pp. [AFS 35; Sender-Empfänger A, D4, G, N, R, ALS 49; Röhren-Sender-Empfänger ARS 80a; Empänger E; Dynamo Maschine B, C, D16, D17, G, R, RS, TL 3,5/20]
• Ref. 186K: "Funkentelegraphie und -telephonie mit ungedämpften Schwingungen" ["Spark gap telegraphy and telephony with undamped waves"], Rudolf Grabau, in "Funkgeschichte", Vol. 29, Nr. 168, 2006, pp. 177-185. Accessed 19 April 2020. [pdf]
• Ref. 186L: "Elektromagnetische Schwingungen und Drahtlose Telegraphie" ["Electromagnetic oscillations and wireless telegraphy"], Jonathan Zenneck, Ferdinand Enke (publ.), 1905, 1056 pp. Source: us.archive.org, accessed 19 April 2020.
• Ref. 186M: "Sendeprinzipien" ["Principles of radio transmitters"], pp. 332-335 in "Radios von gestern: Das Sachbuch für Sammler und Radio-Amateure", Ernst Erb, 3^rd ed., 1998, 456 pp. Source: radiomuseum.org, accessed 19 April 2020 [pdf]
• Ref. 186N: "Historical remarks to the history of electrical oscillators", Wolfgang Mathis, in "Proc. of the International Symp. on Mathematical Theory of Networks and Systems (MTNS)", Padua/Italy, 1998, 4 pp. Source: www.researchgate.net. Accessed 1 May 2020.
• Ref. 186P: "Die Technik der Funkentelegraphie mit gedämpften Schwingungen", ["Spark gap telegraphy and telephony with damped waves"], Rudolf Grabau, in "Funkgeschichte", Vol. 29, Nr. 167, 2006, pp. 136-147. Source: radiomuseum.org, accessed 19 April 2020. [pdf]
• Ref. 186Q: articles by and about Karl Ferdinand Braun
• Ref. 186Q1: "Notizen über drahtlose Telegraphie" ["Notes on wireless telegraphy"], Ferdinand Braun, in "Physikalische Zeitschrift", Vol. 4, Nr. 13, 1 April 1903, p. 361-364. Provides §1 "Zur Beseitigung eines Missverständnisses. Einige historische Bemerkiungen" ["Clearing up of a misunderstanding. Some historical comments"] with brief overview of transmitter technology of those days (Hertz, Marconi, Righi oscillator, spark gap, Slaby, Ascoli, Abraham, antenna reflector), and §2 "Versuche über eine Art gerichteter Telegraphie" ["Tests with a form of directive telegraphy]).
• Ref. 186Q2: "Ferdinand Braun - A Pioneer in Wireless Technology and Electronics", Peter Russer, pp. 228-247 in Section III of "A Wireless World. One Hundred Years since the Nobel Prize to Guglielmo Marconi", Firenze University Press (publ.), first edition, 2012, 370 pp. Source: researchgate.net, retrieved 1 May 201.
• Ref. 186Q3: "Electrical oscillations and wireless telegraphy", Karl Ferdinand Braun, 1909 Nobel Prize in Physics acceptance lecture, Stockholm, December 1909. Source: nobelprize.org, retrieved 3 May 2021.
• Ref. 186R: "Klystrons, Traveling Wave Tubes, Magnetrons, Crossed-field Amplifiers, and Gyrotrons", A. S. Gilmour, Artech House (publ.), February 2011, 864 pp., ISBN 9781608071845.
• Ref. 186S: "The Magnetron", Albert W. Hull, in "Journal of the American Institute of Electrical Engineers", Vol. XL, Nr. 9, September 1921, pp. 715-723. Source: hathitrust.org, retrieved 17 April 2021.
• Ref. 186T: "The Cavity Magnetron: not just a British invention", Yves Blanchard, Gaspare Galati, Piet van Genderen, in "IEEE Antennas and Propagation Magazine", Vol. 55, No. 5, October 2013, pp. 244-254. Source: ieeexplore.ieee.org, accessed 26 April 2021. [pdf, See note 1]
• Ref. 186V: "The Marconi timed-spark continuous-wave transmitter", Philip R. Coursey, in "The Wireless World", Vol. VII, No. 78, September 1919, pp. 310-316. Source: worldradiohistory.com, retrieved 3 May 2021.
• Ref. 186W: "Fessenden and the early history of radio science", John S. Belrose, in "Proceedings of the Radio Club of America", Vol. 67, Nr. 2, November 1993, pp. 6-23. Source: worldradiohistory.com, retrieved 1 April 2021.
• Ref. 186X: "Half a century since the wireless world began", A.D. Blumlein, in "The Wireless World", Vol. 67, No. 4, April 1961, pp. 155-183. Source: worldradiohistory.com, retrieved 3 May 2021.
• Ref. 186Y: multiple articles about WW1 Telefunken's spark transmitter and U-boat radio technology in "Telefunken-Zeitung, Zweite Kriegsnummer, Vol. III, Nr. 16, July 1919". Source: radiomuseum.org, accessed 28 May 2021. [pdf]
• Ref. 187: Telefunken Compass
• Ref. 187A: articles about the German Fog Signal Service and the "Seezeichenversuchsfeld" (Maritime Navigation Markers Test Site)
• Ref. 187A1: "Elektrische Wellen im Nebelsignaldienst" ["Electrical waves in the Fog Signal Service"], Walter Körte, pp. 570-571 in "Zentralblatt der Bauverwaltung", Nr. 87, 30 October 1909. Source: digital.zlb.de. Retrieved February 2020.
• Ref. 187A2: "Die Entwicklung des deutschen Seezeichen-Versuchswesens" ["The development of the German maritime signalling research institute"], Breuer, in "Zentralblatt der Bauverwaltung", Vol. 50, Nr. 1, 8 January 1930, pp. 44–46. Source: digital.zlb.de. Retrieved 17 April 2020.
• Ref. 187A3: "Das Seezeichen-Versuchsfeld des Reichsverkerhsministeriums in Berlin-Friedrichshagen" ["The maritime signalling test site of the Ministry of Transport in Berlin-Friedrichshafen], Breuer, in "Zentralblatt der Bauverwaltung", Vol. 50, Nr. 25, 25 June 1930, pp. 452-457, and Nr. 26, 2 July 1930, pp. 467-471. Source: digital.zlb.de. Retrieved 17 April 2020.
• Ref. 187A4: "Nautischer Verein zu Bremen" ["The Nautical Association in Bremen"], in "HANSA, Deutsche Nautische Zeitschrift", Vol. 50, No. 49, 6 December 1913, p. 1034. Source: digishelf.de. Retrieved 16 April 2020.
• Ref. 187A5: "Funknavigation (Seefunkfeuer) - Arbeiten der preußischen und deutschen Seezeichen Verwaltung und des Seezeichenversuchsfeld - Eine Zusammenfassung der Entwicklungsgeschichte der funktechnischen Seezeichen aus Akten von 1905 - 1939; Teil 1 (1905 - 1910)", Johannes Braun, 1962. Source: web.archive.org (part 2 not available). Retrieved 17 April 2020.
• Ref. 187A6: "Geheimer Oberbaurat Körte" ["Privvy Counsel Körte"], Roloff, in "Zentralblatt der Bauverwaltung", Vol. 34, Nr. 39, 16 May 1914, pp. 297-298. Source: digital.zlb.de. Retrieved 17 April 2020.
• Ref. 187A7: "Die Versuche der deutschen Verwaltung mit elektrischen Wellen im Nebelsignaldienst (Funkfeuer / Seefunkfeuer)" ["Experiments by the Authorities with electrical waves in the Fog Signal Service (radio beacons / maritime radio beacons)"], Johannes Braun, Fachstelle der WSV für Verkehrstechnik (publ.), Koblenz 1962. [Summary]. Retrieved in part from web.archive.org on 25 February 2020
• Ref. 187B: p. 3 in "Telefunken und der deutsche Schiffsfunk, 1903 - 1914" ["Telefunken and German marine radio"], Michael Friedewald, in "Zeitschrift für Unternehmensgeschichte", Vol. 46, Issue 1, April 2001, pp. 27-57. Retrieved 19 April 2020. [pdf]
• Ref. 187C: Telefunken-Kompass; 3 near-identical Telefunken articles. [Summary]
• Ref. 187C1: "Telefunken-Kompass", in "Dinglers Polytechnisches Journal", Year 93, Vol. 327, No. 34, 24 August 1912, pp. 538–541. Source: DFG Digitalisierung des Polytechnischen Journals (Creative Commons 3.0 license).
• Ref. 187C2: "Telefunken-Kompass", pp. 77-84 in "Telefunken Zeitung", Vol. 1, Nr. 5, April 1912. Source: radiomuseum.org.
• Ref. 187C3: "Telefunken Kompass", in "Jahrbuch der drahtlosen Telegraphie und Telephonie sowie des Gesamtgebietes der elektromagnetischen Schwingungen", Nr. 1, July 1912, pp. 85-92, Nr, 2, September 1912, p. 198.
• Ref. 187D: "Telefunken-Kompaß", pp. 15 & 17 in "Telefunken Zeitung", Vol. 2, Nr. 7, August 1912. Source: radiomuseum.org.
• Ref. 187E: articles from the "Popular Science Monthly" magazine.
• Ref. 187E1: "Safeguarding Vessels by Radio" [Bellini-Tosi directional receiver, Telefunken Compass], Annis Salsbury, in "Popular Science Monthly", Vol. 88 [file size: 92 MB], No. 3, March 1916, pp. 451-453. Retrieved 15 April 2020.
• Ref. 187E2: "How the Zeppelin Raiders Are Guided by Radio Signals", in "Popular Science Monthly, Vol. 92" [file size: 92 MB], No. 4, April 1918, pp. 632-634. Retrieved 27 February 2020.
• Ref. 187F: "50 Jahre Telefunken - Festschrift zum 50 jährigen Jubileum der Telefunken Gesellschaft für drahtlose Telegraphy m.b.h. - Gleichzeitig als 100. Ausgabe der Telefunken Zeitung", Vol. 26, Nr. 100, May 1953, 164 pp. Source: nvhrbiblio.nl, retrieved 19 February 2020.
• Ref. 187F1: "Die Zeit des Funkensenders" [The era of the spark gap transmitters], J. Zenneck, pp. 153-158.
• Ref. 187F2: "Fernsehen, Richtstrecken und Funkortung" [Television, directional microwave links, and radio D/F], W.T. Runge, pp. 181-190.
• Ref. 187G: "Meißner, Alexander (Meissner)", pp. 92-93 in "Biografien österreichischer Physiker - Eine Auswahl", D. Angetter, M. Martischnig, Österreichisches Staatarchiv, 2005, 175 pp.
• Ref. 187H: "Orientierung von Luftschiffen" ["Airship navigation"], pp. 110, 111, 114 in "Telefunken Zeitung", Vol. 2, Nr. 11, April 1913. Source: radiomuseum.org.
• Ref. 187J: "Der Peilsender Kleve der Kaiserlichen Marine in Hau" ["The directional beacon (Telefunken Compass station) of the Imperial Navy at Kleve/Hau", Bernd-Rüdiger Ahlbrecht, pp. 20-24 in "Geschichtsbrief Bedburg-Hau", Nr. 14, 2019, Geschichtsverein Bedburg-Hau e.V. (publ.),72 pp. Accessed 15 April 2019.
• Ref. 187K: p. 71 in "Die Antenne - Zeitschrift für drahtlose Nachrichtenübermittlung und verwandte Gebiete", Dr. Erich F. Huth G.m.b.H. – Gesellschaft für Funkentelegraphie (publ.), Vol. 2, Nr. 4, July 1913. Source: de.wikipedia.org.
• The same image is also used on p. 408 of "Das deutsche Seezeichenwesen – 1850–1990 zwischen Segel- und Container-Schiffsverkehr", Gerhard Wiedemann (ed.), Johannes Braun, Hans Joachim Haase, DSV Verlag (publ.), Hamburg 1998, 640 pp.
• Ref. 187L: "Meißner, Alexander, Funkingenieur" [radio engineer], 3-page bio, pp. 695-697 in "Maly - Melanchton", Vol. 16 of "Neue deutsche Biographie", Otto zu Stolberg-Wernigerode (ed.), Duncker & Humblot (publ.), 1990, 785 pp. Accessed 16 April 2020.
• Ref. 187M: "Telefunken auf der Allgemeinen Luftschiff-Ausstellung (Ala)", pp. 53-56 in "Telefunken Zeitung", Vol. 1, Nr. 5, April 1912. Source: radiomuseum.org. [pdf].
• Ref. 187N: "The Radio Direction Finder", Chapter XXII (pp. 261-265) in "History of Communications-Electronics in the United States Navy", Linwood S. Howeth, Bureau of Ships and Office of Naval History, 1963, 698 pp. Source: hathitrust.org, retrieved May 2020.
• Ref. 187P: Appendix A3 (pp. 33-43) in "Fire Island Lighthouse and Keeper's Dwelling", Vol. 3 of "Historic Structure Report", 470 pp. Source: US National Archives and Records Service. [file size: 37 MB]. Retrieved 2 May 2020.
• Ref. 187Q: articles [in Dutch] in "Radio-Nieuws - Maandblad van de Nederlandsche Vereeniging voor Radiotelegrafie". Source: nvhrbiblio.nl. Accessed: 13 April 2020.
• Ref. 187Q1: "Een geheimzinnig station" ["A mysterious station"], Vol. 1, No. 3, 1 March 1918, p. 40.
• Ref. 187Q2: "Geheimzinnige stations" ["Mysterious stations"], Vol. 1, No. 4, 1 April 1918, pp. 82-84.
• Ref. 187Q3: "De A. B. C. stations" ["The A.B.C. stations"], Vol. 1, No. 5, 1 May 1918, pp. 89-90.
• Ref. 187Q4: "De B.C.-stations" ["The B.C.-stations"], Vol. 1, No. 6, 1 June 1918, pp. 125-128.
• Ref. 187Q5: "Nog eens het CCC-station" ["Once more, the CCC-station], Vol. 2, No. 2, 1 February 1919, pp. 33-35.
• Ref. 187Q6: "Is het toch Kleef geweest?" ["Was it Cleves after all?"], Vol. 2, No. 3, 1 March 1919, pp. 70-71.
• Ref. 187Q7: "Nog eens het CCC-station" [Once more, the CCC-station"], Vol. 2, No. 3, 1 March 1919, pp. 71-73.
• Ref. 187Q8: "Weer het CCC-station" ["Again, the CCC-station"], Vol. 2, No. 4, 1 April 1919, pp. 115.
• Ref. 187Q9: "Het b-station" ["The b-station"], Vol. 2, No. 12, 1 December 1919, p. 405-409.
• Ref. 187R: "Die Richtungssendeanlagen Cleve und Tondern" ["The directional transmitting stations Cleve and Tondern], pp. 961-964 in "Die Funkpeilung", Leo Pungs, F. Banneitz, Section 3 of Chapter VI of Part 5 in "Taschenbuch der drahtlosen Telegraphie und Telephonie", Vol. 1, F. Banneitz (ed.), Springer-Verlag (publ.), 1927, 1254 pp.
• Ref. 188: List of 1929-1940 patents of the Conz company (and its employees) regarding frequency conversion and motor speed control; source: DEPATISnet (search-engine of the German patent & trademark office, DPMA).
• Ref. 212: "Flugzeug-Ausrüstungsgeräte - Teil 9, Mappe 637", RLM, Jan/Sept 1944; source: www.DeutscheLuftwaffe.de [file size 41 MB]
• Ref. 212A: pdf pp. 17, 18, 330-350, 388-392
• Ref. 212B: pdf p. 299 "Prüfuhr Ln 28901, PrU 28, 124-1416 A, T. Bäuerle u. Söhne, 1941/42"
• Ref. 228: Rotating loop- and reflector-beacons
• Ref. 228A: "Directional Wireless as an Aid to Navigation" [direction-finding, night effect, course-ranges, directional transmission, beam, VHF reflector-antenna, rotating loops, fixed-course loops], R.L. Smith-Rose, in "Nature", Volume 120, No. 3030, 26 November 1927, p. 774-776. Accessed 11 April 2020. [pdf]
• Ref. 228B: "Some experiments on the applications of the rotating-beacon transmitter to marine navigation", R.L. Smith-Rose, S.R. Chapman, in "Journal of the Institution of Electrical Engineers", Vol. 3 , Iss. 8, March 1928, pp. 256-269, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf]
• Ref. 228C: "Directional Wireless and Marine Navigation: the Rotating-Loop Beacon", R.L. Smith-Rose, in "Nature", Volume 121, 12 May 1928, p. 745.  [pdf]
• This is an update to ref. 228A.
• Ref. 228D: "Radio Direction-Finding by Transmission and Reception", R.L. Smith-Rose, in "Nature", Vol. 125, No. 3154, 12 April 1930, pp. 568-569. [pdf]
• Ref. 228E: "Some Observations on the Orfordness Rotating Beacon", R.L. Smith-Rose, in "Journal of the I.E.E.", Vol. 69, Iss. 412, April 1931, pp. 523-532, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf]
• Also published under the same title in "Proceedings of the Wireless Section of the Institution of Electrical Engineers", Vol. 6, Iss. 17/18 , June-September 1931, pp. 137-146. [Abstract].
• Ref. 228F: Reports of the UK Department of Scientific and Industrial Research, Radio Research Board (DSIR 11):
• Ref. 228F1: "An investigation of a Rotating Radio Beacon" [Gosport], R.L. Smith-Rose, S.R. Chapman, Research Report No. 6, 1928.
• Ref. 228F2: "The Orfordness Rotating Beacon and Marine Navigation" [principle of the beacon, bearing taking with stopwatch and automatic recorder, bearing accuracy], R.L. Smith-Rose, Special Report No. 10, 1931, 14 pp. [Abstract / report review].
• Ref. 228G: pp. 200-204 in "Rotating beacons", Section 4.12 of "Radio Aids to Civil Navigation", Reginald Frederick Hansford (ed.), Heywood & Co. Ltd. (publ.), 1960, 623 pp.
• Ref. 228H: British Air Ministry Notices/Pamphlets
• Ref. 228H1: "Orfordness Rotating Beacon : Instructions for taking bearings. (Provisional) : direction and position finding by means of directional wireless transmission", Pamplet No. 38, year unknown.
• Ref. 228H2: "Orfordness Rotating Radio Beacon", Notice No. 56 of 1929, in "Air Ministry Notices to Airmen, p. 1045 in "Flight", Vol. XXI, no. 38, 20 September 1929, 56 pp. Source: archive.org. Accessed 3 May 2020.
• Ref. 228H3: "Orfordness rotating radio beacon", General Notice No. 19 of 1930.
• Ref. 228H4: "Farnborough Rotating Wireless Beacon", General Notice No. 31 of 1930, in "Air Ministry Notices to Aircraft Owners and Ground Engineers", p. 1388 in "Flight", Vol. XXII, No. 48, 28 November 1930. Source: archive.org. Accessed 3 May 2020.
• Ref. 228H5: "Farnborough rotating wireless beacon" - General Notice No. 33 of 1930.
• Ref. 228H6: "Farnborough and Orfordness rotating wireless beacons", Notice No. 43 of 1931 Series A, p. 823 in "Flight", Vol. XXIII, No. 33, 14 August 1931, 26 pp. Source: archive.org. Accessed 4 May 2020.
• Ref. 228H7: "Orfordness rotating radio beacon", Notice No. 21 of 1932 Series A, p. 499 in "Flight", Vol. XXIV, No. 23, 3 June 1932, 22 pp. Source: archive.org. Accessed 3 May 2020.
• Ref. 228H8: "Orfordness rotating radio beacon", Notice No. 58 of 1932 Series A.
• Ref. 228H9: "Orfordness and Tangmere rotating radio beacons", Notice No. 30 of 1933 Series A.
• Ref. 228H10: "Orfordness rotating radio beacon", Notice No. 63 of 1933 Series A.
• Ref. 228H11: "Orfordness radiobeacon", Notice No. 32 of 1938. Excerpt.
• Ref. 228J: "Direction-Finding System (Beacon)", UK Parliament, Commons Chamber, Record of Oral Answers To Questions, Vol. 222, nr. 29, 21 November 1928. Source: hansard.parliament. Accessed 3 May 2020.
• Ref. 228K: "First of the Beams", 9 pp. in "Inter-War Years", Chapter 5 in "Most Secret: The Hidden History of Orford Ness", Paddy Heazell, The History Press (publ.), 2011, 256 pp. Accessed 4 May 2020. [pdf]
• Ref. 228L: "Note on a special dial for time-pieces to be used with rotating wireless or other beacons", R.L. Smith-Rose, in "Journal of Scientific Instruments", Vol. 5, No. 3, 1 March 1928, pp. 93-96 [file size: 49 MB], . Accessed 4 May 2020.
• Ref. 228M: "An automatic recorder of signals from a rotating beacon transmitter", R.L. Smith-Rose, H.A. Thomas, in "Journal of Scientific Instruments", Vol. 8, No. 3, 1 March 1931, pp. 81-88, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]   Also published in "The Nautical Magazine", Vol. 127, January 1932 [2-page extract].
• Ref. 228N: pp. 35, 36, 79, 87, 154 in "1939 Radio Aids to Navigation - Including Details of Direction-finder Stations, Radiobeacons, Navigational Warnings, Time Signals, Etc.", United States Hydrographic Office (Navy Dept., Bureau of Navigation), publication H.O. No. 205, 1939, 315 pp.
• Ref. 228P: "The invention of synchronous rotations by means of Paul la Cour's Phonic Wheel as used in Telegraphy", P. Chr. Dresing, in "The Telegraphic Journal and Electrical Review", Vol. XX, No. 476, 7 January 1887, pp. 31, 32.
• Ref. 228Q: "Orford Ness: the Black Beacon and associated power house", National Heritage List for England (NHLE). Accessed 8 May 2020. [pdf]
• Ref. 228R: pp. 454-455 in "Wireless - A treatise on the theory and practice of high-frequency electric signalling" [Farnborough rotating beacon], L.B. Turner, Cambridge University Press (publ.), 1931, 531 pp. Source: archive.org [file size: 32 MB]. Accessed 10 May 2020.
• Ref. 228S: articles in "Journal of the Institution of Electrical Engineers", Vol. 66, Iss. 375, March 1928.
• Ref. 228S1: "Rotating-loop radio transmitters, and their application to direction-finding and navigation", T.H. Gill, N.F.S. Hecht, in "Journal of the Institution of Electrical Engineers", Vol. 66, Iss. 375, March 1928, pp. 241-255, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]. Also reprinted in "Proceedings of the Wireless Section of the Institution of Electrical Engineers", Vol. 3, Iss. 8, June 1928, pp. 69-83.
• Ref. 228S2: "Some experiments on the applications of the rotating-beacon transmitter to marine navigation", R.L. Smith-Rose, S.R. Chapman, in "Proceedings of the Wireless Section of the Institution of Electrical Engineers", Vol. 3, Iss. 8, June 1928, pp. 256 -269, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1].
• Ref. 228S3: "A theoretical discussion of various possible aerial arrangements for rotating-beacon transmitters", R.L. Smith-Rose, in "Journal of the Institution of Electrical Engineers", Vol. 66, Iss. 375, March 1928, pp. 270-279, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1].
• Ref. 228S4: "Discussion on the papers “Rotating-loop radio transmitters, and their application to direction-finding and navigation”, by Messrs. Gill and Hecht, “Some experiments on the applications of the rotating-beacon transmitter to marine navigation”, by Messrs. Smith-Rose and Chapman, and “A theoretical discussion of various possible aerial arrangements for rotating-beacon transmitters”, by Dr. Smith-Rose, respectively, before the Wireless Section, 4th January, 1928", in "Journal of the Institution of Electrical Engineers", Vol. 66, Iss. 375, March 1928, p. 274-278. Source: en.booksc.org, accessed April 2021. [pdf, See note 1].
• Ref. 228S5: "The authors' replies to the discussion on “Rotating-loop radio transmitters, and their application to direction-finding and navigation”, “Some experiments on the applications of the rotating-beacon transmitter to marine navigation” and “A theoretical discussion of various possible aerial arrangements for rotating-beacon transmitters”, T.H. Gill, N.F.S. Hecht, R.L. Smith-Rose, S.R. Chapman, in "Journal of the Institution of Electrical Engineers", Vol. 66, Iss. 375, March 1928, pp. 278-279. Source: en.booksc.org, accessed April 2021. [pdf, See note 1].
• Ref. 228T: documentation about the Orfordness beacon, available at The National Archives, Kew/England
• Ref. 228T1: "COMMUNICATIONS. Wireless: Orfordness; erection of an experimental wireless rotating beacon", archive file Catalog reference T 161/576/1, file covers period 24 May 1928 - 4 May 1933.
• Ref. 228T2: "Signals (Code 133): Rotating wireless beacon - Orfordness. Key number(s): 5688, 4496....", archive file Catalog reference MT 9/1951, file covers period 1928 - 1930, file contains 14 items.
• Ref. 228U: p. 345, 346 in "New Aids to Navigation and Pilotage", K.E.L. Creighton, in "Royal United Services Institution Journal", Vol. 77, Iss. 506, May 1932, pp. 341-358. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 228V: articles about Marconi's (and others') parabolic reflector antenna beacons, the Marconi company, and Guglielmo Marconi himself.
• Ref. 228V1: "The "Radio Lighthouse" - An Amazing New Use for Marconi Beams", p. 77 in "Popular Science Monthly", Vol. 105, No. 6, December 1924. Accessed 10 May 2020.
• Ref. 228V2: "Short-wave Directional Wireless Telegraph" [reflector antennas, Inchkeith beacon], C.S. Franklin, in "Nature", Vol. 110, No. 2754, 12 August 1922. Accessed 10 May 2020. [pdf]
• Ref. 228V3: "The Marconi wireless beam reflector on Inchkeith", N. Wells, in "Engineering", Vol. 119, 13 March 1925, p. 309-311.
• Ref. 228V4: pp. 10-13 in "Short wave wireless communication", Alan Wilfrid Ladner, Charles Robert Stoner, John Wiley & Sons, Inc. (publ.), 1933, 348 pp. Source: hathitrust.org, retrieved 20 October 2020.
• Ref. 228V5: pp. 442-444, 455 in "Wireless: A Treatise On The Theory And Practice Of High-Frequency Electric Signalling", L. B. Turner, Cambridge University Press, 1931, 578 pp. Source: archive.org, retrieved 20 October 2020.
• Ref. 228V6: "Short-wave directional wireless telegraphy", C.S. Franklin, in "The Wireless World and Radio Review",Vol. X, No. 8, 20 May 1922, p. 219-225. Source: worldradiohistory.com, retrieved 13 January 2021.
• Ref. 228V7: "Directional short - wave wireless telephony", §6 in "Electrons, electric waves and wireless telephony - XIX", J.A. Fleming, in "The Wireless World and Radio Review", No. 182 (Vol. XI, No. 19), 10 February 1923, p. 626-629. Source: archive.org, retrieved 13 January 2021.
• Ref. 228V8: "Directional wireless as an aid to navigation", in "The Wireless World and Radio Review", No. 189 (Vol. XI, No. 26), 31 March 1923, pp. 859-860. Source: archive.org, retrieved 13J anuary 2021.
• Ref. 228V9: "How Marconi has conquered fogs with a lightless lighthouse - revealing secrets of the wireless wizard's new "one way" radio which may supplant light buoys and other signal devices guiding ships at sea", in "The Shreveport Times" (Shreveport/USA), Vol. L, No. 96, 3 September 1922, p. 35.
• Ref. 228V10: "The wireless beam" [Marconi, reflector beam at Inchkeith, shipping], in "The Manchester Guardian", 15 May 1924, p. 16
• Ref. 228V11: "Safeguarding sea with beam transmitters - Radio beacon guides ships despite fog: Marconi invention safeguards vessels" [Marconi revolving reflector at South Foreland, narrow beam, wavelength 6 m = 50 MHz, 16 compass points marked with Morse coder letter, shipping], in "The Pittsburgh Post", Vol. 83, No. 303, 18 November 1925, p. 13.
• Ref. 228V12: "Reflected wave employed as lighthouse off Scotland" [Marconi, Inchkeith, 4.28 m wavelength = 70 MHz, revolving reflector antenna, 8m aperture, 1/2 rpm, spark transmitter, distinctive signal at 1/2 or 1/4 compass points, Morse letter each 2 compass points, 2.8° bearing determination, stop watch method], in "Calgary Herald" (Alberta/Canada), Vol. 38, No. 4539, 26 August 1922, p. 28.
• Ref. 228V13: "Short wave directive radio transmission" [experiments at ca. 30 MHz (10 m wavelength), 50 W tube transmitter, vertical cage dipole with parabolic reflector], Francis W. Dunmore, Francis H. Engel, in "Radio News", Vol. 5, No. 2, August 1923, pp. 128-130, 182, 184. Source: worldradiohistory.com, retrieved 4 April 2021. Also published as "Short-wace
• Ref. 228V14: "Radio Telegraphy" [Inchkeith beacon], Senatore Guglielmo Marconi, in "Proc. of the IRE", Vol. 10, Nr. 4, August 1922, pp. 215-238.  Source: worldradiohistory.com, retrieved 19 April 2021. Reprint: in "Proc. of the IRE", Vol. 50, Nr. 8, August 1962, pp. 1748-1757. Source: en.booksc.org, accessed April 2021. [pdf (better quality than the scan of the 1922 article), See note 1]
• Ref. 228V15: "A history of the Marconi Company", W.J. Baker, St. Martin's Press (publ.), 1971, 433 pp. Source: nvhrbiblio.nl, retrieved 3 May 2021.
• Ref. 228V16: "The Heinrich Hertz wireless experiments at Karlsruhe in the view of modern communication", D.J. Cichon, W. Wiesbeck, in "Proc. IEE International Conference on 100 Years of Radio", London/UK, September 1995, 6 pp. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 228W: "East coast beacon for airmen" [Orfordness rotating radio beacon operational], in "The Manchester Guardian", 10 September 1929, p. 6.
• Ref. 228X: "Wireless apparatus", R. L. Smith-Rose, in "Journal of Scientific Instruments", Vol. 8, nr. 2, February 1931, pp. 66-69. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 228Y: "A Method of Exciting the Aerial System of a Rotating Radio Beacon", H.A. Thomas, in "Institution of Electrical Engineers - Proceedings of the Wireless Section of the Institution", Vol. 10, Iss. 30, September 1935, 256-261. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 228Z: "Radio Research", S.K. Lewer, in "Science Progress in the Twentieth Century", Vol. 25, No. 98, October 1930, pp. 315-319.
• Ref. 229: civil equi-signal beam systems (Scheller, Fixed-course & Four-Course ranges, E/T & A/N beacons, Visual Ranges, Visual Aural Ranges)
• Ref. 229A: articles in German and Dutch language
• Ref. 229A1: "Über die Wirkung von Schellers drahtlosen Kursweiser auf das Flugzeug" ["About the impact of Scheller's wireless direction pointer on aircraft", Eberhard Buchwald, in "Zeitschrift für drahtlose Telegraphie und Telephonie sowie des Gesamtbereichs der elektromagnetischen Schwingungen", Vol. 15, Nr. 2, February 1920, pp. 114-122. Source: hathitrust.org, retrieved April 2021.
• Ref. 229A2: "Neue Versuche über funkentelegraphische Richtsender" ["New trials with directional spark transmitter stations"; A/N system], Franz Kiebitz, in "Zeitschrift für drahtlose Telegraphie und Telephonie sowie des Gesamtbereichs der elektromagnetischen Schwingungen", Vol. 15, Nr. 4, April 1920, pp. 299-310.
• Ref. 229A3: "Zur Geschichte der Richtwirkungs- und Peilversuche auf den Flugplätzen Döberitz und Lärz" ["History of radio directivity- and direction-finding tests at Döberitz and Lärze airfields"], Richard Baldus, Eberhard Buchwald, Rudolf Hase, in "Jahrbuch - Zeitschrift für drahtlose Telegraphie und Telephonie", Vol. 15, Nr. 2, February 1920, pp. 99-100. Source: hathitrust.org, retrieved April 2021.
• Ref. 229A4: "Über Richtempfangsversuche im Flugzeug" ["About directional reception in airplanes"], Eberhard Buchwald, in "Jahrbuch - Zeitschrift für drahtlose Telegraphie und Telephonie", Vol. 15, Nr. 2, February 1920, pp. 101-113. Source: hathitrust.org, retrieved April 2021
• Ref. 229A5: "Das Kaiserliche Telegraphen-Versuchsamt" ["The Imperial Telegraphy Test Institute"], in "Telefunken Zeitung", Vol. 3, No. 1, January 1914, pp. 7-9. Source: radiomuseum.org, retrieved 11 April 2021.
• Ref. 229A6: "Neuere Arbeiten auf dem Funkbaken-Gebiete" ["Recent work in the field of radio beacons"; Lorenz, E/T keying, magnetic-bias keying, VHF beacon], Ernst Kramar, "Hochfrequenztechnik und Elektroakustik", Vol./Nr. 40, September 1932, pp. 88-92. [Abstract].
• Ref. 229A7: "Lorenz-ultra-korte golf-landingsbaken voor vliegtuigen" ["Lorenz VHF landing beacon for aircraft"], H. Veenstra (Lorenz; based on E. Kramar), in "Radio-Nieuws", Vol. 18, Nr. 3, 15 May 1935, pp. 49-61. Source: nvhrbiblio.nl, retrieved 24 May 2022.
• Ref. 229A8: "De Nederlandsche radiobakens" ["The Dutch radio beacons"; incl. B.R.A. 101], pp. 59-66 in "Radio en Luchtvaart" ["Radio and aviation"], S. van der Molen, No. 5 of "Meulenhoff's Luchtvaartserie", J.M. Meulenhoff (publ.), 1936, 107 pp. Source: us.archive.org, retrieved 22 May 2022.
• Ref. 229B: "Radio range flying", C.H. McIntosh, J.L. Adams, F.C. Ringer, Ringer Press (publ.), 1941, 62 pp. Source: hathitrust.org, retrieved 1 April 2021.
• Ref. 229C: articles in "Electrical Communication - Technical Journal of the International Telephone and Telegraph Corporation and Associate Companies". Source: worldradiohistory.com. Accessed January-August 2020.
• Ref. 229C1:"Otto Scheller and the Invention and Applications of the Radio-Range Principle" [incl. ITT Landing System, SCS-51 (mobile)], R.I. Colin, in "ITT Electrical Communication", Vol. 40, Nr. 3, 1965, pp. 359-368, retrieved 23 January 2020. [Summary]. Reprinted as "Otto Scheller: The Radio Range Principle", R.I. Colin, in "IEEE Trans. on Aerospace and Electronic Systems", Vol. AES-2, No. 4, July 1966, pp. 481-487 [pdf].
• Ref. 229C2: "Federal Telephone and Radio Corporation - A historical review: 1909-1946" [incl. spark transmitter, arc transmitter, Duddell, Poulsen, Federal Telegraph Company, Mackay System, ITT], F.J. Mann, in "ITT Electrical Communication", Vol. 23, No. 4, December 1946, pp. 377-406.
• Ref. 229C3: "An Ultra-High Frequency Radio Range with Sector Identification and Simultaneous Voice", Andrew Alford, Armig G. Kandoian, Frank J. Lundburg, Chester B. Watts, in "Electrical Communication" Journal of the Int'l Telephone & Telegraph Corp. and Associated companies", Vol. 23, No. 2, 1946, pp. 179-189.
• Ref. 229D: Papers published in the "Bureau of Standards Journal of Research". Source: US National Institute of Standards and Technology (NIST). Accessed March-April 2020. Also articles about activities of the Bureau of Stds.
• Ref. 229D1: "A 12-Course Radio Range for Guiding Aircraft with Tuned Reed Visual Indicator", H. Diamond, F.G. Kear, Research Paper 154 (RP154), in "Journal of Research", Vol. 4, Issue 3, March 1930, pp. 351-369. [pdf] [Abstract]
• Ref. 229D2: "Applying the Radio Range to the Airways", F.G. Kear, W.E. Jackson, Research Paper 155 (RP155), in "Journal of Research", Vol. 4, Issue 3, March 1930, pp. 371-381. [pdf] [Abstract]. NOTE: this article was also published in the Proc. of the IRE, see ref. 229L8.
• Ref. 229D3: "Development of the Visual Type Airway Radio-Beacon System", J.H. Dellinger, H. Diamond, F.W. Dunmore, Research Paper RP159, in "Journal of Research", Vol. 4, Issue 3, March 1930, pp. 425-459.  [pdf]   [Abstract, Summary]
• Ref. 229D4: "The cause and elimination of night effects in radio range-beacon reception", H. Diamond, Research Paper 513 (RP513), in "Journal of Research", Vol. 10, Issue 1, January 1933, pp. 7-34. [pdf]
• Ref. 229D5: "A radiobeacon and receiving system for blind landing of aircraft", H. Diamond, F.W. Dunmore, Research Paper 238 (RP238), in "Journal of Research", Vol. 5, Issue 4, October 1930, pp. 897-931. [pdf]
• Ref. 229D6: "Unidirectional radiobeacon for aircraft", E.Z. Stowell, Research Paper 35 (RP35), in "Journal of Research", Vol. 1, Issue 6, December 1928, pp. 1011-1022. [pdf]   [Abstract]
• Ref. 229D7: "Applying the visual double-modulation type radio range to the airways", Research Paper 148 (RP148), H. Diamond, in "Journal of Research", Vol. 4, Issue 3, March 1930, pp. 265-289. [pdf]   [Abstract]
• Ref. 229D8: "A course-shift indicator for the double-modulation type radiobeacon", H. Diamond, F.W. Dunmore, Research Paper 77 (RP77), in "Journal of Research", Vol. 3, Issue 1, 1 July 1929 (paper dates from 20 February 1929), 10 pp. [pdf]
• Ref. 229D9: "A tuned-reed course indicator for the 4 and 12 course aircraft radio range", F.W. Dunmore, Research Paper RP160, in "Journal of Research", Vol. 4, Issue 4, April 1930, pp. 461-474. [pdf]   [Abstract]
• Ref. 229D10: "Design of tuned reed course indicators for aircraft radiobeacon", F.W. Dunmore, Research Paper 28 (RP28), in "Journal of Research", Vol. 1, Issue 5, November 1928, pp. 751-769. [pdf, file size: 26 MB]
• Ref. 229D11: "A method of providing course and quadrant identification with the radio range-beacon system" [Adding a vertical antenna to the cross-loops], F.W. Dunmore, Research Paper 593 (RP593), in "Journal of Research", Vol. 11, Issue 3, September 1933, pp. 309-325. [pdf] [Abstract]
• Ref. 229D12: "The Radio Work of the Dept. of Commerce", J.H. Dellinger, in "QST", June 1921, pp. 18-21. Accessed 14 April 2020. [pdf]
• Ref. 229D13: "A Century of WWV", Glenn K. Nelson, in "Journal of Research of the National Institute of Standards and Technology", Vol. 124, Article 124025, 2019. Accessed 14 April 2020. [pdf]
• Ref. 229D14: "Radio publications of the Bureau of Standards", NBS DoC, Letter Circular LC 40, 25 November 1922, 22 pp. Accessed 14 April 2020. [pdf]
• Ref. 229D15: "Radio - The aviator's guiding hand", pp. 147-170 in "Antennas, instruments, and systems in development" Chapter VI in "Achievement in Radio - Seventy Years of Radio Science, Technology, Standards, and Measurements at the National Bureau of Standards" [file size: 72 MB; history of the NBS radio section], Wilbert F. Snyder, Charles L. Bragaw, National Bureau of Standards, NIST Special Publication 55 (SP555), October 1986, 884 pp. Accessed 14 April 2020. [pdf, file size: 72 MB]
• Ref. 229D16: "Automatic volume control for aircraft radio receivers", W.S. Hinman, Research Paper 330 (RP330), in "Journal of Research", Vol. 7, Issue 1, July 1931, pp. 37-46. Accessed 15 July 2020. [pdf]
• Ref. 229D17: "A Course Indicator of Pointer Type for the Visual Radio Range-Beacon System", F.W. Dunmore, Research Paper 336 (RP 336), in "Journal of Research", Vol. 7, Issue 1, July 1931, pp. 147-170. Accessed 5 June 2020. [pdf] [Abstract]
• Ref. 229D18: "Theory of design and calibration of vibrating-reed indicators for Radio Range beacons", G.L. Davies, in "Journal of Research", Vol. 7, Issue 1, July 1931, pp. 195-213. Accessed 10 June 2020. [pdf] [Abstract] NOTE: this article was also published in the Proc. of the IRE, see ref. 229L13.
• Ref. 229D19: "A simultaneous radiotelephone and Visual Range beacon for the airways", F.G. Kear, G.H. Wintermute, Research Paper 341 (RP341) in "Journal of Research", Vol. 7, Issue 2, August 1931, pp. 261-287. Accessed 10 June 2020. [pdf] [Abstract] NOTE: this article was also published in the Proc. of the IRE, see ref. 229L7.
• Ref. 229D20: "Phase Synchronization in Directive Antenna Arrays with Particular Application to the Radio Range Beacon", F.G. Kear, Research Paper 581 (RP581), in "Journal of Research", Vol. 11, No. 1, July 1933, pp. 123-140. [pdf] [Abstract]
• Ref. 229D21: "A course-shift indicator for the double-modulation type radiobeacon", H. Diamond, F.W. Dunmore, in "Journal of Research", Vol. 3, Issue 1, July 1929, p. 1. [pdf]
• Ref. 229D22: "Graphical determination of polar patterns of directional antenna systems", G.L. Davies, W.H. Orton, Research Paper 435 (RP435), in "Journal of Research", Vol. 8, Issue 5, May 1932, pp. 555-569. [pdf]
• Ref. 229D23: "Performance tests of radio system of landing aids", H. Diamond, Research Paper 602 (RP602), in "Journal of Research", Vol. 11, Issue 4, October 1933, pp. 463-490. [pdf] [Abstract]
• Ref. 229D24: "A radio direction finder for use on aircraft", Wilbur S. Hinman, Research Paper 621 (RP621), in "Journal of Research", Vol. 11, Issue 6, December 1933, pp. 733-741. [pdf] [Abstract]
• Ref. 229D25: "Experiments with underground ultra-high-frequency antenna for airplane landing beam", Harry Diamond, Francis W. Dunmore, Research Paper 1006 (RP1006), in "Journal of Research", Vol. 19, Nr.1, July 1937, 19 pp. [pdf] [Abstract]. NOTE: this article was also published in the Proc. of the IRE, see ref. 229L17.
• Ref. 229D26: "Consolidated Instrument Company" & "The Radio-beacon Tuned Reed Indicator", pp. 44 & 74 in "US Air Services - Feature Aeronautical Magazine, Commercial and Military", November 1929. [contract to manufacture the U.S. Bureau of Standards Visual Radio beacon Vibrating Reed Indicator awarded to Julien P. Friez & Sons, Inc., Baltimore/MD, subsidiary of Consolidated Instrument Co. of America, Inc.].
• Ref. 229D27: "The comparative accuracy of various existing and proposed radio navigation systems" [Radio Range, azimuthal-type, hyperbolic-type, composite range/azimuth type], William Q. Chrichlow, National Bureau of Standards, Central Radio Propagation Laboratory [ = Department of Commerce, Boulder/CO, Laboratories Building 1], Report No. CRPL-4-1, 30 December 1946, 44 pp. Source: nist.gov, retrieved 20 October 2020.
• Ref. 229D28: "Receiving sets for aircraft beacon and telephony", Haraden Pratt, Harry Diamond, in "J. of Research", Vol. 1, Issue 4, October 1928, pp. 543-563, Research Paper 19 (RP19), 19 June 1928, 23 pp. Source: nist.gov, retrieved 23 February 2021.
• Ref. 229D29: "Characteristics of airplane antennas for radio range-beacon reception" [vertical, T-, L-, V-antennas] H. Diamond, G.L. Davies, in "J. of Research", Vol. 6, Issue 5, May 1931, pp. 901-916, Research Paper 313 (RP313), 24 January 1931, 16 pp. Source: nist.gov, retrieved 23 February 2021.
• Ref. 229D30: "Theory of design and calibration of vibrating reed indicators for radio range beacons", G.L. Davies, in "J. of Research", Vol. 7, Issue 1, July 1931, pp. 195-213, Research Paper 338 (RP338), 25 March 1931, 19 pp. Source: nist.gov, retrieved 23 February 2021.
• Ref. 229E: Papers published in "Scientific Papers of the Bureau of Standards". Source: US National Institute of Standards and Technology (NIST). Accessed April 2020.
• Ref. 229E1: "A Directive Type of Radio Beacon and its Application to Navigation" [test/eval of multi-turn crossed-loop antennas, A/N equi-beam, effect of aircraft trailing-wire receive antenna], F.H. Engel, F.W. Dunmore, in "Scientific Papers of the Bureau of Standards", Vol. 19, No. 480 (S480), 8 September 1923, pp. 281-295.  [pdf] [Summary]
• Ref. 229E2: "Directive radio transmission on a wave length of 10 meters" [successful experiments of making the radiation pattern of a vertical dipole directional, with various configs of a reflector screen made of tuned & un-tuned vertical wires; shortwave, instead of then-standard long & medium wave], Francis W. Dunmore, Francis H. Engel, in "Scientific Papers of the Bureau of Standards", Vol. 19, Scientific Paper No. 469 (S469), 9 January 1923, pp. 1-16. [pdf] Extract was publised as "Short-wave directive transmission - constructional details of the transmitting and receiving equipment", in "The Wireless World and Radio Review", No 202 (Vol. XII, Nr. 13), 30 June 1923, pp. 419- 422. Source: worldradiohistory.com, retrieved 21 April 2021.
• Ref. 229E3: "Principles of radio transmission and reception with antenna and coil aerials", J.H. Dellinger, Scientific Paper No. 354 (S354), Scientific Papers of the Bureau of Standards, Vol. 15, June 1919, pp. 435-495. [pdf]
• Ref. 229E4: "The radio direction finder and its application to navigation", Frederick A. Kolster, Francis W. Dunmore, Scientific Paper 428 (S428), July 1921), Scientific Papers of the Bureau of Standards, Vol. 17, January 1922, pp. 529-566. [pdf]
• Ref. 229E5: "The field radiated from two horizontal coils", G. Breit, Scientific Paper No. 431 (S431), Scientific Papers of the Bureau of Standards, Vol. 17, Issue 3, 1922, pp. 589-606. [pdf]
• Ref. 229F: web page "The Evolution of Airway Lights and Electronic Navigation Aids", Roger Mola, U.S. Centennial of Flight Commission, 2003. [pdf]
• Ref. 229G: "The Equi-Signal Zone Radio Beacon and Air Navigation", R.L. Smith-Rose, in "Nature", Vol. 126, No. 3168, 19 July 1930, pp. 98-100. Accessed 1 March 2020. [pdf]
• Ref. 229H: Yagi-Uda directional multi-element focussed beam antenna
• Ref. 229H1: "Projector of the Sharpest Beam of Electric Waves", Hidetsugu Yagi, Shintaro Uda, in "Proceedings of the Imperial Academy" (Japan), Vol. 2, Iss. 2, 1926, pp. 49-52. [pdf]
• Ref. 229H2: p. 214 in "Highlighting the History of Japanese Radio Astronomy: 1: An Introduction", M. Ishiguro, W. Orchiston, K. Akabane, N. Kaifu, M. Hayashi, T. Nakamura, R.Stewart, H.Yokoo, in "Journal of Astronomical History and Heritage", Vol. 15, No. 3, November-December 2012, pp. 213-231. Source: narit.or.th, retrieved 8 April 2021
• Ref. 229H3: "Notes on the history of the Yagi-Uda antenna", Yasuto Mishiake, in "IEEE Antennas and Propagation Magazine", Vol. 56, No. 1, february 2014, pp. 256-257. Source: sm.rim.or.jp, retrieved 5 April 2021.
• Ref. 229J: "Lighting the Airways" and "The Emergence of Radio", in Chapter II "The Republican Era, 1926-1932", in "Bonfires to beacons: Federal civil aviation policy under the Air Commerce Act, 1926-1938" [file size: 29 MB], Nick A. Komons, U.S. Department of Transportation / Federal Aviation Administration (publ.), 1978, 472 pp. Source: hathitrust.org, accessed 21 May 2020. 
• Ref. 229K: "Radio range and blind flying: almost a decade of monumental aeronautical growth (1929-1936)", Chapter 4 (pp. 105-144) in "Flying the beam: navigating the early US airmail airways, 1917-1941", Henry R. Lehrer, Purdue University Press (publ.), ISBN 9781557536853, 2014, 234 pp.
• Some pages from Chapter 4.
• Ref. 229L: articles in Proceedings of the Institute of Radio Engineers. Source: worldradiohistory.com, retrieved June 2014 - June 2020.
• Ref. 229L1: "Apparatus used on British and European Airways", Edward H. Furnival, in "Proc. of the I.R.E", Vol. 17, Nr. 12, December 1929, pp. 2123-2136.
• Ref. 229L2: "The civil airways and their radio facilities", H.J. Walls, in "Proc. of the I.R.E.", Vol. 17, Nr. 12, December 1929, pp. 2141-2157.
• Ref. 229L3: "Applying the visual double-modulation type Radio Range to the airways", H. Diamond, in "Proc. of the I.R.E", Vol. 17, Nr. 12, December 1929, pp. 2158-2184. [Abstract]
• Ref. 229L4: "Radio in aeronautics - Its technical status and the organization for its application in Germany", F. Eisner, H. Fassbender, in "Proc. of the I.R.E.", Vol. 17, Nr. 12, December 1929, pp. 2185-2229.
• Ref. 229L5: "Applying the Radio Range to the airways", F.G. Kear, W.E. Jackson, in "Proc. of the I.R.E.", Vol. 17, Nr. 12, December 1929, pp. 2268-2282.   [Abstract]. NOTE: this article was also published in the Bureau of Standards Journal of Research, see ref. 229D2.
• Ref. 229L6: "Radio beacons for transpacific flights", Clayton C. Shangraw, in "Proc. of the I.R.E.", Vol. 16, Nr. 9, September 1928, pp. 1203-1235. [Abstract].
• Ref. 229L7: "A simultaneous radiotelephone and Visual Range beacon for the airways", F.G. Kear, G.H. Wintermute, in "Proc. of the I.R.E.", Vol. 20, Nr. 3, March 1932, pp. 478-515. NOTE: this article was also published in the Bureau of Standards Journal of Research, see ref. 229D18. [Abstract].
• Ref. 229L8: "Development of radio aids to air navigation", J.H. Dellinger, Haraden Pratt, in "Proc. of the I.R.E.", Vol. 16, No. 7, July 1928, pp. 890-920. [Abstract].
• Ref. 229L9: "Apparent Night Variations with Crossed-coil Radio Beacons", Haraden Pratt, in "Proc. of the I.R.E.", Vol. 16, Nr. 5, May 1928, p. 652-657. [Abstract].
• Ref. 229L10: "Simultaneous Radio Range and Telephone Transmission", W.E. Jackson, D.M. Stuart, in "Proc. of the I.R.E.", Vol. 25, Nr. 3, March 1937, pp. 314-326.  [Abstract].
• Ref. 229L11: "Radio Guidance" [two rotating radio beacons (simultaneously on the same frequency), triangulation on a display (physical map in aircraft instrument + projecting 2 intersecting light beams)], J. Edward Miller, in "Proc. of the I.R.E.", Vol. 20, Nr. 11, November 1932, pp. 1752-1762. [Abstract].
• Ref. 229L12: "Loop antennas for aircraft" [D/F], George F. Levy, in "Proc. of the I.R.E.", Vol. 31, Nr. 2, February 1943, pp. 56-66. [Abstract].
• Ref. 229L13: "Theory of design and calibration of vibrating-reed indicators for Radio Range beacons", G.L. Davies,  in "Proc. of the I.R.E.", Vol. 20, Nr. 1, January 1932, pp. 161-181. [Abstract]. NOTE: this article was also published in the Bureau of Standards Journal of Research, see ref. 229D17.
• Ref. 229L14: "The Development of a Visual Type of Radio Range Transmitter Having a Universal Application to the Airways" [very comprehensive!!! 4-course, 12-course visual range, transmitters, frequency tripler, loops, goniometer], W.E. Jackson, S.L. Bailey, in "Proc. of the IRE", Vol. 18, Nr. 12, December 1930, pp. 2059-2101. [Abstract]
• Ref. 229L15: "A Radio Range beacon free from night effects", Howard Allan Chinn, in "Proc. of the I.R.E.", Vol. 21, Nr. 6, June 1933, pp. 802-807.
• Ref. 229L16: "On the solution of the problem of Night Effects with the Radio Range beacon system", H. Diamond, in "Proc. of the I.R.E.", Vol. 21, Nr. 6, June 1933, pp. 808-832. [Abstract]
• Ref. 229L17: "Rectangular short-wave frame aerials for reception and transmission", L.S. Palmer, D. Taylor, in "Proc. of the I.R.E.", Vol. 22, Nr. 1, January 1934, pp. 93-114
• Ref. 229L18: "Experiments with underground ultra-high-frequency antenna for airplane landing beam", Harry Diamond, Francis W. Dunmore, in "Proc. of the I.R.E.", Vol. 25, Nr. 12, December 1937, pp. 1542-1560. [Abstract] Note: this article was also published in the Bureau of Standards Journal of Research, see ref. 229D25.
• Ref. 229L19: "The status of instrument landing systems" [overview BoS activities, test at College Park/MD & Newark, Lorenz 1933 40 MHz and kick-meter, US Army 1932/33 at Wright Field, Lorenz/ITT tests at Indianapolis issues, Bendix/UAL tests 1936 with yagi antennas], William Elvin Jackson, in "Proc. of the I.R.E.", Vol. 26, Nr. 6, June 1938, pp. 681-699. [Abstract]. Note: same article was also published in 1937 as CAA Technical Development Report No. 1 (ref. 229R20).
• Ref. 229L20: "The Ultra-Short-Wave Guide-Ray Beacon and Its Application", E. Kramar, W. Hahnemann, in "Proc. of the I.R.E.", Vol. 26, No.1, January 1938, pp. 17-44.
• Ref. 229L21: "Ultra-Short-Wave Propagation", Paul von Handel, Wolfgang Pfister, in "Proc. of the IRE", Vol. 25, Nr. 3, March 1937, pp. 346-363.
• Ref. 229L22: "Field intensity characteristics of double modulation type of directive radio beacon", Haraden Pratt, in "Proc. IRE", vol. 17, Nr. 5, May 1929, pp. 873-878. Source: worldradiohistory.com, retrieved 23 February 20121.
• Ref. 229M: "Adcock Antennas" [4-Course A/N systems], section 1.13.3 in "Radio Antenna Engineering", Edmund A. Laport, McGraw-Hill Book Co. (publ.), 1952, 574 pp.
• Ref. 229N: "The stationary and rotating equisignal beacon" [Bellini-Tosi, goniometer, Telefunken Compass, A/N fixed-course, tests at McCook Field / Dayton, and Wilbur Wright Field, loop crossing-angle effects], W. H. Murphy, L. M. Wolfe, in "SAE Transactions", Vol. 21, Part II, 1926, pp. 979-1015.
• Ref. 229P: articles about Australian "Marconi" Radio Range, Lorenz/AWA beams & ILS
• Ref. 229P1: "First radio beacon in Australia opened by the Minister for Defence", p. 3 in "The Radiogram - The Staff Journal of the Amalgamated Wireless (Australasia) Ltd.", Vol. III, no. XIII, July 1936. Source: worldradiohistory.com, retrieved 15 June 2020.
• Ref. 229P2: p. 128, 148, 149 in "Air Crash: the story of how Australia's airways were made safe, Vol. 1 - 1929-1939", Macarthur Job, Aerospace Publications Australia (publ.), 1991, 169 pp.
• Ref. 229P3: "Wireless - Radio for aircraft" [equisignal beacons should be established], in "The Sydney Morning Herald", Vol. 100, 7 Feb 1930, p. 5.
• Ref. 229P4: "Radio beacon - First in Australia - Opened near Mascot - Range up to 200 miles", in "The Sydney Morning Herald", Vol. 106, 28 April 1936, p. 10.
• Ref. 229P5: "Radio beacons - Air Board perplexed" [new beacon system (VHF) suggested, just before MW beacon tenders considered], in "The Age" (Melbourne), 26 January 1937, p. 9.
• Ref. 229P6: "Ultra Short Wave - Air-routes installation", [VHF beacons to be installed on main air routes], in "The Age" (Melbourne), 4 March 1937, p. 10.
• Ref. 229P7: "Radio to aid airmen- Six new beacons - Plans for network completed", in "The Sydney Morning Herald", Vol. 107, 29 May 1937, p. 17, 18.
• Ref. 229P8: "Aviation - Air beacons - Installation in Australia - Progressive radio" [Lorenz/Germany staff supervises installation of beacons; equipment imported and manufactured by AWA], in "The Sydney Morning Herald", Vol. 107, 4 December 1937, p. 16.
• Ref. 229P9: "Radio beam might have saved Kyeema - Evidence of expert - The beam was found satisfactory" and "Beacons tests - Plane chartered" [accident investigation; Lorenz VHF beacon at Essendon & Canberra ground test soon], in "The Age" (Melbourne), 3 November 1938, p. 13.
• Ref. 229P10: "Radio aids to flying - Tests begin", in "The Sydney Morning Herald" [accident investigation; Lorenz & AWA receivers, VHF ], Vol. 108, 5 November 1938, p. 13.
• Ref. 229P11: "Kyeema disaster inquiry - Suitability of new beacons - World's best safety factors", in "The Age" (Melbourne), 5 November 1938, p. 32.
• Ref. 229P12: "Board's lack of plane - Many requests - Needed for beacon tests - Government's delay", in "The Sydney Morning Herald", Vol. 108, 8 November 1938, p. 8.
• Ref. 229P13: "Air beacons - "We lead the world" - Captain Johnston at Kyeema Inquiry" [accident investigation; MW vs VHF beacons, AWA experimental receiver, Philips "blind landing" beacon system did not meet Civil Aviation Board specs], in "The Sydney Morning Herald", Vol. 108, 24 November 1938, p. 12.
• Ref. 229P14: "Airlines and activities - First radio beacons to-day - Sidney-Brisbane route" [all beacons along route operational this day], in "The Age" (Melbourne), 3 April 1939, p. 9.
• Ref. 229P15: "Radio beacons - First manufacture in Australia", in "The Sydney Morning Herald", Vol. 109, 7 April 1939, p. 8.
• Ref. 229P16: "Airlines and activities - Beacon made in Australia - Useful development" [VHF beacons, first at Sydney/Kingford-Smith, equipment designed & made by AWA, 90 ft steel tower], in "The Age" (Melbourne), 13 April 1939, p. 9.
• Ref. 229P17: "Air navigation aids - Four beacons at work" [8 of 10 beacons tested, 4 of which already operational], in "The Sydney Morning Herald", Vol. 109, 7 June 1939, p. 21.
• Ref. 229P18: "History of radio beacons - Delays in operation - Evidence on tests and experiments" [Lorenz & Telefunken beacons, STC, suitability of German receivers], in "The Age" (Melbourne), 4 November 1938, p. 7.
• Ref. 229P19: "Fault in air beacons - Steel towers may go - Long series of delays", in "The Sydney Morning Herald", Vol. 109, 28 November 1939, p. 12.
• Ref. 229P20: "Australia perfects radio guide" [claims Australian scientists first in world to perfect DME], in "The Sydney Morning Herald", Vol. 118, 8 January 1949, p. 3.
• Ref. 229P21: "Radio aids for safer flying" [Radio Ranges, ILS, DME], in "The Sydney Morning Herald", Vol. 120, 19 September 1950, p. 2.
• Ref. 229Q: "Principles of Aeronautical Radio Engineering", P.C. Sandretto, McGraw-Hill Book Co. (publ.), 1^st ed., 1942, 424 pp. Source: us.archive.org [file size 20 MB], retrieved 15 June 2020.
• Chapters II-VIII: "The Radio Range", "The Ultra-High-Frequency Radio Range", "Aircraft Direction Finders", "Markers", "Instrument Landing", "Absolute Altimeters", "Direction Finding from Ground Stations".
• Key words: radio ranges; derivation of loop antenna field-strength pattern; goniometer; apparent/phantom loop vs. physical/true loop; course-shifting & -bending; TL range antenna system; "night effect" elimination; Simultaneous Radio Range (beacon + voice); Visual Radio Range; reed instruments; 12-course (never in service); UHF radio range; shore-effect (dielectric constant & soil conductivity); multiple/split courses (altitude dependent); TL tower; Alford Loop; Visual 2-Course Range (90/150 Hz modulation + 1020 Hz A/N quadrant ID & station passage); RCA VHF Omni-directional range (VOR) being developed (1942), preceded by LW omni with rotating goniometer + north signal; cardioid pattern; ILS (Lorenz, Bureau of Standards, United-bendix, CAA-ITT, Washington Institute of Technology, CAA-MIT), Dingley leader cable, altimeters (sonic, capacitive, radio).
• Ref. 229R: US Dept. of Commerce, bi-weekly Air Commerce Bulletins (ACB) 1929-1939, Aeronautics Bulletin (AB) 1936, monthly Civil Aeronautics Journals (CAJ) 1944-1950, Technical Development Reports (TDR), Technical Manuals (TM), Miscellaneous Publications (MP). Source ACB: hathitrust-org, source AB: hathitrust.org; source CAJ: hathitrust.org (1) and  hathitrust.org (2);  retrieved June-September 2020. Source TM: hathitrust.org, retrieved February 2021; [abstracts/summaries of all ACB & CAAJ articles below]
• Ref. 229R1: ACM, Vol. 1 (July-December 1929, January-June 1930) [abstracts / summaries] ‒
  No. 2 (July-'29), pp. 19-20, No. 3 (Aug-'29), p. 13, No. 4 (Aug-'29), pp. 5-11, 21-23, No. 5 (Sept-'29), pp. 10-11, No. 8 (Oct-'29), pp. 15-17, No. 10 (Nov-'29), pp. 1-3,  No. 11 (Dec-'29), pp. 11-12, 29, No. 12 (Dec-'29), p13, No. 13 (Jan-'30, pp. 19-20, No. 14 (Jan-'30), p. 18, No. 15 (Feb-'30), p. 18,  No. 16 (Feb-'30), pp. 14,  No. 18 (Mar-'30), p. 16,  No. 19 (Apr-'30), p. 15, No. 22 (May-'30), pp. 3-8, No. 23 (June-'30), pp. 5-6, No. 24 (June-'30), p. 9.
• Ref. 229R2: ACM, Vol. 2 (July-December 1930, January-June 1931) [abstracts / key words] ‒
  No. 4 (Aug-'30), pp. 79-87, No. 5 (Sept-'30), pp. 120-121, No. 8 (Oct-'30), pp. 201-203, No. 10 (Nov-'30), pp. 272-275, No. 14 (Jan-'31), pp. 366-367, 370-371, No. 15 (Feb-'31), pp. 393, No. 17 (Mar-'31), pp. 437-439, No. 20 (Apr-'31), pp. 526-529.
• Ref. 229R3: ACM, Vol. 3 (July-December 1931, January-June 1932) [abstracts / summaries] ‒
  No. 3 (Aug-'31), pp. 55-58, No. 4 (Aug-'31), p. 102, No. 8 (Oct-'31), p. 109, No. 15 (Feb'-32), pp. 361-365, No. 18 (Mar-'32), pp. 433-438, 440, 441.
• Ref. 229R4: ACM, Vol. 4 (July-December 1932, January-June 1933) [abstracts / summaries] ‒
  No. 2 (July-'32), pp. 33-45, No. 5 (Sept-'32), pp. 121-126,  No. 6 (Sept-'32), pp. 135-150, No. 11 (Dec-'32), pp. 260-264, No. 12 (Dec-'32), pp. 293-294, No. 17 (Mar-'33), pp. 424-426, No. 18 (Mar-'33), pp. 441-427, No. 19 (Apr-'33), pp. 467-469, 470-472, No. 21 (May-'33), pp. 525-529, No. 22 (May-'33), pp. 555-569.
• Ref. 229R5: ACM, Vol. 5 (July-December 1933, January-June 1934) [abstracts / summaries] ‒
  No. 1 (July-'33), pp. 3-7, 16, No. 5 (Nov-'33), pp. 127-133, No. 7 (Jan-'34), pp. 165-168, No. 8 (Feb-'34), pp. 202, No. 9 (Mar-'34), pp. 223-225, No. 11 (May-'34), pp. 265-271.
• Ref. 229R6: ACM, Vol. 6 (July-December 1934) [abstracts / summaries] ‒
  No. 3 (Sept-'34), pp. 55-59, No. 5 (Nov-'34), pp. 108, 109.
• Ref. 229R7: ACM, Vol. 8 (July-December 1936, January-June 1937) [abstracts / summaries] ‒
  No. 3 (Sept-'36), pp. 65-70, No. 4 (Oct-'36), pp. 83-93, No. 5 (Nov-'36, pp. 127-129, No. 8 (Feb-'37), pp. 169-175.
• Ref. 229R8: ACM, Vol. 9 (July-December 1937, January-June 1938) [abstracts / summaries] ‒
  No. 4 (Oct-'37, pp. 77-85, No. 5 (Nov-'37) , p. 119, No. 6 (Dec-'37), pp. 141-143, No. 8 (Feb-'38), pp. 189-191, No. 12 (June-'38), pp. 304-306.
• Ref. 229R9: ACM, Vol. 10 (July-December 1938, January-June 1939) [abstracts / summaries] ‒
  No. 4 (Oct-'38), p. 116, No. 12 (June-'39), p. 301.
• Ref. 229R10: AB, No. 24 (1936), "The federal airways system" [incl. airway operations, intermediate landing fields, optical airway beacons, radio range beacons (types RA, RL, MRA, MRL, ML), radio communication stations, weather service], U.S. Dept. of Commerce, Bureau of Air Commerce, 1 July 1936, 25 pp.
• Ref. 229R11: ACM, Vol. 11 (July-December 1939) [abstracts / summaries] ‒
  No. 5 (Nov-'39), pp. 121, 124, No. 6 (Dec-'39), pp. 155-157.
• Ref. 229R12: CAJ, Vol. 1 (1940)  [abstracts / summaries] ‒
  No. 3 (Feb-'40, pp. 37, 38, 52), No. 7 (Apr-'40, pp. 109-111, 156.
• Ref. 229R13: CAJ, Vol. 5 (1944) [abstracts / summaries] ‒
  No. 3 (Mar-'44, pp. 29, 39, No. 12 (Dec-'44), p. 140.
• Ref. 229R14: CAJ, Vol. 6 (1945) [abstracts / summaries] ‒
  No. 2 (Feb-'45), pp. 13, 17.
• Ref. 229R15: CAJ, Vol. 7 (1946) [abstracts / summaries] ‒
  No. 6 (June-'46), pp. 72, 78, No. 7 (July-'46), pp. 85, 95, No. 11 (Nov-'46), pp. 137, 142, 148, No. 12 (Dec-'46), p. 150.
• Ref. 229R16: CAJ, Vol. 8 (1947) [abstracts / summaries] ‒
  No. 3 (Mar-'47), pp. 30, 31, 33, No. 4 (Apr-'47, pp. 37, 44.
• Ref. 229R17: "Circuit design for low-frequency radio ranges" [general description, field intensity distributions, coupling system, antenna currents, phase between antenna pairs vs. course shift, equipment], Donald M. Stuart, "CAA Technical Development Report No. 23 (formerly CAA Technical Development Div. Report No. 8)", November 1939, 23 pp. Source; hathitrust.org, retrieved 26 June 2020.
• Ref. 229R18: "Visual-Aural Ranges and Omniranges", Bulletin No. 3 of "CAA Airways Operations Training Series", March 1949, 24 pp. Source: hathitrust.org, retrieved 26 June 2020.
• Ref. 229R19: "Flying the Omnirange", Department of Commerce,  Civil Aeronautics Administration, Aviation Information, June 1950. 24 pp. Source: hathitrust.org, retrieved 26 June 2020. Revised version was issued by the CAA as "Basic omnirange flying", February 1951, 9 pp.
• Ref. 229R20: "The status of instrument landing systems" [NBS, Lorenz system, Army Air Force, Washington Institute of Technology, Indianapolis, Transcontinental / Western Air / United Airlines, Bendix], William Elvin Jackson, Department of Commerce, Bureau of Air Commerce, Civil Aeronautics Authority, Safety and Planning Division, Technical Development Report No. 1 (formerly CAA Technical Development Report No. 1 (TDR 1), October 1937, 15 pp. Source: hathitrust.org, retrieved 1 July 2020. [Abstract]. Note: this article was also published in 1938 the Proc. of the I.R.E. (ref. 229L19).
• Ref. 229R21: "Preliminary report on a four course ultra-high-frequency radio range", J.C. Hromada, Dept. of Commerce, Bureau of Air Commerce, Safety and Planning Division, Technical Development Report No. 3 (TDR 3, formerly Report No. 3), January 1938, 7 pp., CAA reprint, 1940. Source: hathitrust.org, retrieved 1 July 2020.
• Ref. 229R22: "Geographical separation of Radio Range stations operating on the same or adjacent frequencies in the 200-400 kilocycle band", A.E. Harrison, U.S. Department of Commerce, Civil Aeronautics Authority, Technical Development Report No. 4, January 1938, 6 pp. Source: hathitrust.org, 16 January 2021.
• Ref. 229R23: "The Ultra-High-Frequency Aural Radio Range", J.C. Hromada, P.B. King, Part I of "Development of the Ultra-High-Frequency Radio Range", U.S. Dept. of Commerce, Civil Aeronautics Administration, Radio Development Section, Technical Development Division, Technical Development Report No. 42, June 1944, 15 pp.
• Ref. 229R24: "Testing of the UHF Radio Ranges and Towers", P.B. King, T.A. Kouchnerkavich, Part II of "Development of the Ultra-High-Frequency Radio Range", U.S. Dept. of Commerce, Civil Aeronautics Administration, Radio Development Section, Technical Development Division, Technical Development Report No. 43, July 1944, 40 pp. [file size: 34 MB]
• Ref. 229R25: "A Visual-Aural Ultra-High-Frequency Radio Range with Simultaneous Voice", Part III of "Development of the Ultra-High-Frequency Radio Range", U.S. Dept. of Commerce, Civil Aeronautics Administration, Radio Development Section, Technical Development Division, Technical Development Report No. 49, June 1945, 116 pp. [file size: 40 MB]
• Ref. 229R26: "Pilots' Radio Handbook" [incl. Visual Radio Range, Aural Radio Range, Omni Range / VOR, ILS], U.S. Dept. of Commerce, Civil Aeronautics Administration (C.A.A.), Technical Manual No. 102, September 1953, revised March 1954, 127 pp. [file size: 31 MB]
• Ref. 229R27: pp. 295-298 in "The tide of commerce and industry (1920-30)", Chapter V (pp. 221-298) in "Measures for Progress - A history of the National Bureau of Standards", Rexmond C. Cochrane, James. R. Newman (ed.), U.S. Dept. of Commerce, Miscellaneous Publication 275 (MP 275), 1966, 683 pp. Source: nist.gov, retrieved 19-Feb-2021.
• Ref. 229R28: "Airplane radio" [1921 NBS support to Army Air Service experiments with loops crossing at 45° for generating equisignal course], p. 68 in "Radio Communication", in "Annual Report of the Director Bureau of Standards to the Secretary of Commerce for the Fiscal Year Ended June 30, 1921", Dept. of Commerce, Miscellaneous Publication No. 47 (MP 47), 1921, 276 pp. Source: digital.library.unt.edu, retrieved 22 February 2021.
• Ref. 229R29: p. 172 in "Some activities and accomplishments", pp. 162-285 in "Standards Yearbook 1927" [covers 1926!] , Dept. of Commerce, Bureau of Standards, Miscellaneous Publication No. 77 (MP77), 12 February 1927, 408 pp. Source: nist.gov, retrieved 13 March 2021.
• Ref. 229R30: p. 76 in "Bureau of Lighthouses", pp. 74-76 in "Standards Yearbook 1928" [covers 1927!], Dept. of Commerce, Bureau of Standards, Miscellaneous Publication No. 83 (M83), 4 January 1928, 399 pp. Source: nist.gov, retrieved 13 March 2021.
• Ref. 229R31: "The development adjustment, and application of the Z-marker" (a higher resolution file is here, file size 43 MB), W.E. Jackson, H.I. Metz, Civil Aeronautics Authority Technical Development Report No. 14 (TDR-14, formerly Report No. 16, Safety & Planning Division, Bureau of Air Commerce, Dept. of Commerce), July 1938, 28 pp. Source: hathitrust.org, retrieved 9 April 2021.
• Ref. 229R32: "The development of fan-type Ultra-High-Frequency radio markers as a traffic control and let-down aid", Henry Irwin Metz, Civil Aeronautics Authority, Technical development Report No. 5 (CAA TDR-5; formerly Report No. 5, Safety & Planning Div., Bureau of Air Commerce, Dept. of Commerce), January 1938, 22 pp.
• Ref. 229R33: "The development of an improved Ultra-High-Frequency radio fan marker", P.D. McKeel, J.M. Lee, H.I. Metz, Civil Aeronautics Authority, Technical development Report No. 12 (CAA TDR-12, formerly Report No. 14, Safety & Planning Div., Bureau of Air Commerce, Dept. of Commerce)), June 1938, 22 pp.
• Ref. 229S: "American Aviation Heritage - Identifying and Evaluating Nationally Significant Properties in U.S. Aviation History, A National Historic Landmarks Theme Study", U.S. Dept. of the Interior, National Park Service, Rev. March 2011, 320 pp. Source: npshistory.com, retrieved 20 June 2020. [pdf]
• Incl.: College Park Airfield/MD (pp. 84-87, p. 261), Army's McCook Field in Dayton/OH (p. 54, 67, 71, 125, 134, 267; all facilities moved to Wright Field in 1927 and was then closed down), Wright Field (also near Dayton/OH, later renamed Wright-Patterson AFB; pp. 3-5, 125, 134-136), Bellefonte/PA Air Mail Field (p. 84, 85, 271; NBS 4-course range test site), Mitchel Field near Garden City/NJ (p. 168)].
• Ref. 229T: articles/books about radio beacons developed and/or installed in France
• Ref. 229T1: "Navigation radioélectrique (principe des appareils)" ["Radio Navigation (principles of the equipment)"; D/F, rotating loop, rotating beacons with radio goniometer, course-beacons, Lorenz & L.M.T. landing systems, ], Ministère des Travaux Public et des Transports, Secrétariat Général à l'Aviation Civile et Commerciale, Section des Instructions Aéronautique, preliminary edition, 1944, 44 pp. Source: calameo.com, retrieved 3 July 2020.
• Ref. 229T2: "Les phares aéronautiques - France, Allemagne, États-Unis, Europe du Nord, 1910-1960" ["Aeronautical beacons - France, Germany, USA, northern Europe"], Collection Mémoire de l'Aviation Civile, Direction Générale de l'Aviation Civile (DGAC), 2018, 99 pp. Source: Ministère de la Transition écologique et solidaire / Mission Mémoire de l'Aviation Civile, retrieved July 2020.
• Ref. 229T3: "Chronique de la navigation aérienne" ["Chronicle of radio air navigation", file size: 30 MB], Jean Hubert, École Nationale de l'Aviation Civile (ENAC, National Civil Aviation School, Toulouse/France, publ.), 1987, 349 pp. Source: Ministère de la Transition écologique et solidaire / Mission Mémoire de l'Aviation Civile, retrieved December 2019. [Notes]
• Ref. 229T4: "Navigation radioélectrique (principe des appareils)" ["Radio navigation - principle of the systems"; radio-goniometer & error sources, automatic goniometer/DF, radio compass, omni-directional radio beacons, fixed & rotating course-beacons, radio altimeter, bad-weather landing methods & beacons, Lorenz], Ministère des Travaux Public et des Transports, Secrétariat Général à l'Aviation Civile et Commerciale, Section des Instructions Aéronautique, preliminary edition, 1944, 44 pp. Source: calameo.com, retrieved 3 July 2020.
• Ref. 229T5: "Phares lumineux ou radiophares?" ["Optical or radio beacons?"], P. Franck, in "L'Aéronautique - Revue mensuelle illustrée", Vol. 9, No. 100, September 1927, pp. 271-274. Source: Bibliothèque National de France (BNF) online library, retrieved 11 July 2020.
• Ref. 229T6: "Un important problème de la navigation áerienne : Le guidage des avions 1-2-3" ["An important problem in aerial navigation: the guidance of aircraft", Parts 1-3], M. Volkringer, in "Revue Aéronautique de France", Vol. 20, No. 3, March-April 1930, pp. 4-6; No. 4, April-May 1930, p. 7; No. 7, July-August 1930, pp. 5-6. Source: Bibliothèque National de France (BNF) online library, retrieved 11 July 2020.
• Ref. 229T7: "L'atterissage sans visibilité des avions par l'emploi des ondes ultra-courtes - 1" ["Aircraft landing without visibility by using ultra-short waves" - Part 1 of 3], Vol. 29, No. 7-8, July-August 1939, pp. 10-12. Source: Bibliothèque National de France (BNF) online library (the library does not hold issues of this magazine with the remaining part(s) of the article), retrieved 7 September 2020.
• Ref. 229T8: "Les radiophares d'atterrissage" ["Radio beacons for landing"], Paul Larivière, in "L'Aéronautique", Vol. 18, No. 207, August 1936, pp. 155-163. Source: Bibliothèque National de France (BNF) online library, retrieved 11 July 2020.
• Ref. 229T9: "Note sur les aériens et les diagrammes de rayonnement des radiophares de guidage à enchevêtrement / Notice concerning the aerials and the diagrams of radiation of the radio range beacons at interlocking signals" [article in both French & English], Yves Rocard, in "Bulletin de la Société Française Radio-Électrique (S.F.R.)", Vol. 11, No. 2, 2^nd Quarter 1937, pp. 33-60. Source: Bibliothèque National de France (BNF) online library, retrieved 11 July 2020.
• Ref. 229T10: "Les radiophares interférentiels S.A.D.O.D.-Aicardi" ["Directional radio beacons of the company Société des Ondes Dirigées (SADOD), system Aicardi], Paul Larivière, in "L'Aéronautique", Vol. 19, No. 219, August 1937, pp. 198-202. Source: Bibliothèque National de France (BNF) online library, retrieved 11 July 2020.
• Ref. 229T11: "Effets de diffraction affectant la signalisation des radioalignements" ["Effects of refraction (shore effect) on the signalling of radio course beacons"], Yves Rocard, in "Revue Scientifique", Vol. 78, No. 5-6, May-June 1940, pp. 267-272. Source: Bibliothèque National de France (BNF) online library, retrieved 11 July 2020.
• Ref. 229T12: "Un dispositif français d'atterrissage sans visibilité" ["A French device for blind landing"], in "Aviation Française", No. 138, 22 October 1947, p. 8. Source: Bibliothèque National de France (BNF) online library, retrieved 11 July 2020.
• Ref. 229T13: "L'atterrissage dans la brume" ["Landing in fog"], Henry Porra, in "Science et Vie", No. 356, May 1947, pp. 223-233. [ZZ method, Toulouse, SCS 51, GCA, CSF].
• Ref. 229T14: "Le temps des ingénieurs de la navigation aérienne - Mémoires techniques 1945-1985" ["The era of radio navigation engineers"; file size: 34 MB], Groupement des Ingénieurs de L'aviation Civile Rétraités (Bordeaux), 2013, 243 pp. Source: calameo.com, retrieved 4 October 2020.
• Ref. 229U: "Report on electronic systems of air navigation - "Technical and economic characteristics of LF/MF non-directional beacons, Standard Loran, Consol [Sonne-Consolan], Navarho, Decca, "GEE" system, LF/MF four-course radio range, VHF omni-directional range, Distance Measuring Equipment", Air Coordinating Committee, Air Traffic Control & Navigation Panel, Special Working Group No. 9; U.S. Dept. of Commerce, Office of Technical Services, March 1954, pp. Source: hathitrust.org, retrieved 1 July 2020.
• Ref. 229V: articles, books, and other material about the history of the U.S. DoC National Bureau of Standards and its beacons
• Ref. 229V1: "History and development of the Bureau of Standards radio beacon experiment station at College Park, Maryland", Robert W. Beckham, 18 December 1936, 40 pp. Records of the Phi Mu Fraternity, Special Collections, University of Maryland Libraries, University of Maryland, College Park. Source: archive.org, retrieved 3 July 2020. [Introduction]
• Ref. 229V2: pp. 293-298, 407 in "Measures for progress: A history of the National Bureau of Standards" [file size: 32 MB], Rexmond C. Cochrane, U.S. Dept. of Commerce, National Bureau of Standards, MP 275, 2^nd ed., 1974, 718 pp. Source: US National Institute of Standards and Technology (NIST),  accessed 3 September 2020. [pdf]
• Ref. 229V3: "The first radio beacon is inaugurated", photo of the interior of the Bureau of Standards beacon radio hut at College Park/MD/USA, with its director, George K. Burgess, 30 May 1927. Retrieved 19 February 2021.
• Ref. 229V4: Historic images in the Digital Archives of the National Institute of Standards and Technology (NIST, Gaithersburg, MD 20899). Records: Dials for blind landing aircraft (Aug. 1930), Blind landing system - 1 (Dec. 1930), Blind landing system - 2 (Dec. 1930), Interior of blind landing system (Dec. 1930), Landing beacon indicator and control panel (April 1930), Aids for blind landing of aircraft (July 1930), College Park field station (1926), Aircraft course indicators using two metal reeds, 1928. Accessed: June-August 2020.
• Ref. 229W: U.S. Dept. of Commerce and US Army Air Forces documents covering air navigation (incl. US radio range maps)
• Ref. 229W1: "Practical air navigation and the use of the aeronautical charts of the Department of Commerce", Thoburn C. Lyon, Special Publication No. 197, U.S. Dept. of Commerce, Coast and Geodetic Survey, 1935, 63 pp. [file size: 23 MB] [p. 36 - Radio Range chart] Source: hathitrust.org.
• Ref. 229W2: "Practical air navigation and the use of the aeronautical charts of the U.S. Coast and Geodetic Survey", Thoburn C. Lyon, Special Publication No. 197, U.S. Dept. of Commerce, Coast & Geodetic Survey, 2^nd ed. (1938), 204 pp. [p. 53 - Radio Range chart] [file size: 52 MB] Source: noaa.gov, accessed 21 July 2020.
• Ref. 229W3: "Practical air navigation", Thoburn C. Lyon, Civil Aeronautics Bulletin No. 24, U.S. Dept. of Commerce, Civil Aeronautics Administration (CAA), September 1940, 263 pp. [p. 97 - Radio Range chart] [file size: 49 MB]. Source: hathitrust.org, accessed 22 July 2020.
• Ref. 229W4: "Practical air navigation", Thoburn C. Lyon, 1945, 359 pp. [p. 200 - Radio Range chart] [file size: 112 MB] Source: hathitrust.org, accessed 23 July 2020.
• Ref. 229W5: "Instrument Flying: Advanced (with Radio Aids)" [incl. A/N Radio Ranges, Marker Beacons], U.S. Army Air Forces, Technical Order No. 30-100B-1, 15 January 1944, 80 pp. Source: aafcollection.info, accessed 23 September 2020.
• Ref. 229W6: "The Evolution of Instrument Flying in the U.S. Army", David M. McIntosh, Air Command and Staff College, Air University, Maxwell AFB, Student Report Nr. 88-1760, April 1988, 65 pp. Source: US Defence Technical Information Center, retrieved 7 October 2020.
• Ref. 229W7: "Civil Aviation and Facilities - Aerospace Education II", N.A. Orser, W.G. Glascoff, US Air Force Junior ROTC, "ED 068 290", 1969, 148 pp. Source: eric.ed.gov, retrieved 1 April 2021.
• Ref. 229X: "Characteristics of Radio Ranges, Elementary Radio Range flying, Instrument Approach Procedures, Radio compasses, Instrument landings and other development projects", Chapters III, IV, V, IX, and X in "Instrument and radio flying" [Radio Ranges, Instrument Approach Procedures, radio compasses, Busignies, Sperry-RCA ADF, Hegenberger, Lorenz, UHF Ranges, Air-Track, RTCA, Bendix System, Metcalf, Flighttray] Karl S. Day, Air Associates, Inc. (publ.), 1938, 284 pp. Source: hathitrust.org, retrieved 8 June 2021.
• Ref. 229Y: articles in popular radio & aviation magazines and newspapers, primarily 1920s-1930s
• Ref. 229Y1: "Radio beacons to aid air mail flyers", R.S. Winters, in "Radio Age", Vol. 7, Nr. 1, September 1927, pp. 21-24, 48. Source: worldradiohistory.com,, retrieved 23 February 2021.
• Ref. 229Y2: "Guiding airplanes by radio beacons", S.R. Winters, in "Popular Aviation", Vol. 1, Nr. 4, November 1927, pp. 23-26.
• Ref. 229Y3: "Landing of aircraft in fog by radio", H. Diamond, in "Electronics", Vol. 6, Nr. 6, June 1933, pp. 158-161. Source: worldradiohistory.com, retrieved 23 February 2021.
• Ref. 229Y4: "Airports and Airways" [radio beacon at Hadley Field], in "Aviation" (pre AvWeek), Vol. 23, No. 1, 29 August 1927, p. 486, 488. Source: us.archive.org, retrieved 24 February 2021.
• Ref. 229Y5: "Federal Airways", Charles Ingram Stanton, in "Radio News", Vol. 29, No. 6, June 1943, pp. 100, 101, 260, 266. Source: worldradiohistory.com, retrieved 1 April 2021.
• Ref. 229Y6: "Radio Ranges", Donald M. Stuart, in "Radio News", Vol. 29, No. 6, June 1943, pp. 126-129, 266, 272. Source: worldradiohistory.com, retrieved 1 April 2021.
• Ref. 229Y7: "Washington plans new radio beacon as aid to flyers" [Bureau of Standards, College Park/MD], in "The Baltimore Sun", Vol. 179, No. 85D, 23 August 1926, p. 7.
• Ref. 229Y8: "Radio beacon guides direction of planes - Army experts report recent experiment worked perfectly" [Army Signal Corps, Bureau of Standards, first beacon guided flight, from Ford Airport to McCook Field], in "The Evening Sun" (Baltimore/MD)", 25 March 1927, p. 40.
• Ref. 229Y9: "Radio beacons will serve planes as direction guides" [Bureau of Standards, College Park/MD, airplane radio telephone, 6 beacon station established or under construction], in "The Hartford Courant", Vol. XC, 22 May 1927, p. 75.
• Ref. 229Y10: "Radio soon practical for airplane service" [College Park/MD, Bellefonte/PA, McCook Field in Dayton/OH; Ford Motor Co. Field Dearborn/MI & Chicago/IL, Hadley Field/NJ], in "The Pittsburgh Press", 5 June 1927, p. 51.
• Ref. 229Y11: "First radio beacon dedicated" [College Park/MD], in "Kenosha Evening News", Vol. XXXIII, No. 194, 10 June 1927, p. 29
• Ref. 229Y12: "The first radio beacon is inaugurated" [photo; College Park/MD, Bureau of Standards], in "Fort Worth Star-Telegram", Vol. XLVII, Nr. 146, 26 June 1927, p. 12.
• Ref. 229Y13: "Radio beacons guide flyers across continent" [radio beacon telephone; photo; College Park/MD, E.Z. Stowell, P.W. Dunmore, H. Pratt, C.B. Hempel, J.H. Dellinger, Bureau of Standards], in "The Hartford Courant", Vol. XC, 26 June 1927, p. 68.
• Ref. 229Y14: "Radio beacons for air-travel over the seas" [photo; J.H. Dellinger, Bureau of Standards, chain of radio beacons across the ocean], in "The Capital Times" (Madison/WI), Vol. 19, No. 18, 2 July 1927, p. 4.
• Ref. 229Y15: "U. S. scientists responsible for radio beacon" [photo; F. Dunmore, J.H. Dellinger, H. Pratt; Bureau of Standards; College Park], in "Fort Worth Star-Telegram", Vol. XLVII, Nr. 202, 21 August 1927, p. 1.
• Ref. 229Y16: "Footnotes" [visual beacon, DoC, BoS, 8 years, College Park], in "Nebraska State Journal", 16 June 1928, p. 6.
• Ref. 229Y17: "Engineers told of government's work on aircraft radio" [1926 Air Commerce Act, Aeronautics Branch, BoS, 1926/27 BoS beacon stations], in "Chicago Sunday Tribune", 17 June 1928, p. 5
• Ref. 229Y18: "Radio beacon is now practical - Enables airmen to fly on course in any weather, engineers say" [Doc, BoS 1921, aural & visual systems, receiving set, indicator], in "New Cambria Leader", Vol. XVI, Nr. 27, 31 August 1928, p. 2.
• Ref. 229Y19: "Flying conquers fog" [BoS, cockpit instruments, reed indicator], James Stokley, in "Oakland Tribune", Vol. CX, No. 48, 17 February 1929, p. 72.
• Ref. 229Y20: "Will conduct "fog flying" radio tests - Efficiency of the aircraft radio beacon to be tried out by Army flyer" [Doolittle, reed instrument, College Park], Martin Codel, in "Great Falls Tribune", Vol. 43, 3 July 1929, p. 13.
• Ref. 229Y21: "Former government scientists carry on aviation research - Radio experts, victims of Economy Act, form institute to pursue navigation developments as private individuals" [BoS, Washington Institute of Technology, at College Park(MD)] in "The Evening Star" (Washington/DC), 13 October 1933, p. 17.
• Ref. 229Y22: "And now... Happy landings for the "blind-flying-"pilot" [combined instrument, light & radio beacons, BoS, TL], J.H. Williams, in "Salinas Index-Journal", Vol. XLIX, 4 November 1933, p. 9.
• Ref. 229Y23: "Landing planes by radio in fog", Keith Wyatt, in "The Baltimore Sun", Vol. 37-D, 4 April 1937, pp. 98, 99.
• Ref. 229Y24: "Medium-wave beacons at Croydon" [335 kHz 4-course radio range; Marconi built?], in "Flight", 26 August 1937, p. 216.
• Ref. 229Z: articles and other material about the Henry Ford A/N radio beacons
• Ref. 229Z1: photos from the digital collection expert set of The Henry Ford, accessed 15 February 2021 - "Radio Beacon Transmitting Station and Antennas at Ford Airport, 10 September 1926" (image THF123653); "Radio Station "WFO" License for Operating the Ford Aircraft Radio Beacon, 26 October 1926" (image THF255154); "Detail of Goniometer Used inside the Radio Beacon Transmitting Station at Ford Airport, 10 September 1926" - (image THF99457), "Equipment Inside the Radio Beacon Station Building at Ford Airport, March 16, 1927" (image THF255074; goniometer motor drive & scale).
• Ref. 229Z2: "Ford Airways complete year's flight; no accident during entire year" [Ford air transport service started 13 April 1925, between Ford Airport at Dearborn/MI & Chicago/Maywood Field; 1 July 1925: between Detroit/MI & Cleveland/OH], in "Ford News", Vol. VI, No. 13, 1 May 1926, pp. 1, 8.
• Ref. 229Z3: "Ford Airways Daily Flight Report" entry of 8 November 1926: 2:25 hr / 230 miles beacon test flight Dearborn-Chicago with Eugene Donovan as "radio man".
• Ref. 229Z4: "Ford radio beacon for airplanes", in "Ford News", Vol. VII, Nr. 10, 15 March 1927, p. 1.
• Ref. 229Z5: "Guiding aerial flight by radio beacon - A process applied to commercial aviation on the Ford Airlines", in "Ford News", Vol. VII, Nr. 12, 1 April 1927, pp. 4, 5.
• Ref. 229Z6: "Ford plane with tour is winged laboratory - Is testing radio beacon, 500-mile telegraphic unit, and broadcast receiving set", in "Ford News", Vol. VII, Nr. 17, 1 July 1927, p. 1, 6.
• Ref. 229Z7: "Plane radio is efficient - In touch with land constantly on tour" [3rd National Air Tour; Ford Co. trimotor equipped with beacon radio equipment, mentions 5 beacons incl. Ford Co. beacon at Dearborn/MI], in "Ford News", Vol. VII, Nr. 19, 1 August 1927, p. 1.
• Ref. 229Z8: "First radio-directed flight" [10 Feb 1928: first official beacon-guided point-to-point flight - Dearborn/MI (Ford) to McCook Field (Army) ], in "Ford News", Vol. VIII, Nr. 6, 1 February 1928, p. 19.
• Ref. 229Z9: "The radio beam - Aviators depend on an invention developed by an automobile company", in "Ford News", Vol. XX, November 1940, p. 247, 262.
• Ref. 229Z10: "Radio beacon used by commercial airplane", William F. Gilmore, in "U. S. Air Services", Vol. XII, Nr. 3, March 1927, p. 15.
• Ref. 229Z11: "The new Ford transport", A.M. Jacobs, p. 68 in "Air Corps News Letter", Vol. XI, No. 3, 10 March 1927. Source: media.defense.gov, retrieved 19 February 2021.
• Ref. 229Z12: "1^st with a radio beam for planes!", 1-page Ford Co. advertising in "Boy's Life - For All Boys" magazine, May 1945, p. 19; on p. 12 in "Life", 5 February 1945; on p. 33 in "Popular Science", January 1945.
• Ref. 229Z13: pp. 204-207 in "Henry Ford: His life - His work - His genius", William Adams Simonds, Floyd Clymer (publ.), 1946 (revised ed.), 365 pp. Source: us.archive.org, retrieved 19 February 2021.
• Ref. 229Z14: "Aircraft Radio Beacon" chapter 10 (pp. 97-100) in "Beyond the Model T - The other adventures of Henry Ford", Ford R. Bryan, Wayne State University Press (publ.), revised edition, 1997, ISBN 0-8143-2682-X, 232 pp.
• Ref. 229Z15: "Ford Airport Hangar", National Register of Historic Inventory - Nomination Form, U.S. Dept. of the Interior, National Park Services, 10 April 1985, 25 pp. Source: catalog.archives.gov, retrieved 15 February 2021. [file size 25 MB] 
• Ref. 229Z16: recommended website "Flying the beams - The history of the Low Frequency Radio Range, aviation's first radio navigation system and other early radio navigation systems through the mid-20th century", Doug Davis, 2021. Accessed April 2021.
• Ref. 229Z17: "How the Ford radio beacon station changed aviation", YouTube video, accessed 15 February 2021.
• Ref. 229Z18: "Lansing Municipal Airport", 4 pp. in "Forgotten Chicago Airfields", Nicolas C. Selig, The History Press (publ.), 2014, 128 pp.
• Ref. 229Z19: "Ford Motor Company" [renewal of license for experimental radio stations W8XC, W9XH, W8XE], pp. 150-153 in "Decisions, reports, and orders of to Federal Communications Commission of the United States - July 1934 - July 1935 - Volume 1", Federal Communications Commission Reports, Federal Communications Commission, 1936, 338 pp.
• Ref. 229Z20: "Radio beacon guides Dayton Ford plane" [first beacon guided flight Ford Airport Dearborn/MI, McCook Field, Dayton/OH], in "St. Joseph Herald-Press" , 11 February 1927, p. 5
• Ref. 229Z21: "Radio beacon control invented" [Ford-Hammond Airport, Dearborn Field], in "The Lake County Times", Vol. XXI, No. 212, 14 April 1927, pp. 1, 21.
• Ref. 229Z22: "New radio beacon for Ford Airport at Lansing" [A/N/T beacon, Lansing & Detroit], in "The Lake County Times", Vol. XVIII, No. 14, 5 May 1928, p. 1.
• Ref. 229Z23: "Model airport opened by Ford" [Detroit, paved runways + taxi ways + aprons], in "The Sunday Star" (Washington/DC), No. 1231, 21 October 1928, p. 72.
• Ref. 229Z24: "Ford radio beacon hearing ordered - Company must show need of continuing service", in "The Detroit Free Press", Vol. 101, Nr. 9, 13 May 1931, p. 9.
• Ref. 229Z25: "Ford engineers designed, built radio beacon - Round-the-world airways system completed by Australia-India link" [Army Air Service fall 1926, BoS, Ford radio range], in "The Daily Republican" (Monongahela/PA), Vol. 98, Nr. 13, 9 June 1944, p. 5.
• Ref. 229Z26: "Radio beacon aids dirigible on flight" [Ford Airport], in "The Sacramento Bee", Vol. 140, No. 22,803, 20 November 1926, p. 40.
• Ref. 229Z27: "Radio beacons test at Ford airport", in "The New York Times", 27 February 1927, Section XX, p. 18.
• Ref. 230: German, British, US WW2 RDF, radio-navigation systems, and associated jamming systems / countermeasures
• Ref. 230A: p. 42 in "The Secret War", Brian Johnson, Pen and Sword (publ.), 2004, 352 pp. [pdf, file size 50 MB] See note 1
• Ref. 230B: Table 1 in "Verfahren und Anlagen der Funkortung" ["Radio-navigation methods and installations"], W. Stanner, in "Elektrotechnische Zeitung (ETZ)", Ausgabe A, Vol. 75, Nr. 13, 1 July 1954, pp. 438-442. [circular LoP, hyperbolic LoP, Consol, Consolor, Decca, Loran, range of various systems incl. "Erika", "Erich", "Hermine", and "Mond"]
• Ref. 230C: "Pulling the crooked-leg", R.V. Jones, in "New Scientist", 23 February 1978, pp. 493-496.
• Ref. 230D: "Most Secret War: Britisch Scientific Intelligence 1939-1945", R.V. Jones, Hamish Hamilton (publ.), 1978, 576 pp. See note 1
• Ref. 230E: "Milestones - Battle of the Beams", Carlo Kopp, in "Defence Today", January/February 2007, pp. 76, 77. [pdf]
• Ref. 230F: "The Battle of the Beams - Part 1-3", D.V. Pritchard (G4GVO), in "Practical Wireless", Vol. 64, No. 1, Issue 970, January 1989, pp. 43-47; No. 2, Issue 971, February 1988, pp. 46-49; No. 3, Issue 972, March 1988, pp. 30-34. Source: worldradiohistory.com, accessed 1 September 2020. Also published as "The Battle of the Beams - Part 1-3", D.V. Pritchard (G4GVO), in "Ham Radio Magazine", June 1989, pp. 29-38; August 1989, pp. 20-29; October 1989, pp. 53-61. Source: worldradiohistory.com, accessed January 2014.
• Ref. 230G: "Chapter II and III in "R. V. Jones and the Birth of Scientific Intelligence", James Martinson Goodchild, PhD thesis, University of Exeter, March 2013, 640 pp. [pdf] Accessed 12 May 2019.
• Ref. 230H: "Electronic Warfare and the Night Bomber Offensive", Rob O'Dell, pp. 97 - 117 in "Air Power Review", Royal Air Force, Volume 10, Number 1, Spring 2007.
• Ref. 230J: "Radio Navigation Systems for Aviation and Maritime Use — A Comparative Study" [RDF, Consol/Consolan, Navaglobe, VOR, VORTAC, VOR/DME, Navarho/Navarho-H/-HH/-Rho, Decca, Standard Loran (Loran-A), Loran-C, Radio Mesh System], W. Bauss (tech ed.), Advisory Group for Aeronautical Research and Development (AGARD), North Atlantic Treaty Organization (NATO), AGARDOgraph 63, Pergamon Press, 1963, 232 pp. Translation of the German publication "Funkortungssysteme für Luft- und Seefahrt - Eine vergleichende Gegenüberstellung", Verkehrs- und Wirtschaftsverl. Dr. Borgmann (publ.). [pdf, file size 58 MB]. The following are articles taken from this book.
• Ref. 230J1: "Radio Direction-Finding on Board Aircraft and Ships", W.T. Runge, pp. 19-28.
• Ref. 230J2: "Consol and Consolan", Ernst Kramar, pp. 29-39.
• Ref. 230J3: "VOR-System", K. Bärner, pp. 43-57.
• Ref. 230J4: "Decca". H. Lueg, pp. 81-101.
• Ref. 230J5: "Standard-Loran", Ernst Kramar, pp. 113-118.
• Ref. 230K: articles about Elektra, Sonne, Consol/Consolan, Elektra-Sonne, Mond
• Ref. 230K1: "The Navigational Beam System "Elektra-Sonne" [Elektra, Sonne, Elektra-Sonne, Mond; complete German description, short translated summary in English], Otto von Heil, FIAT Final Report No. 1105, Field Information Agency Technical (FIAT), US Office of Military Government for Germany, 17 June 1947, 177 pp. Source: www.cdvandt.org. Accessed: March 2019.
• Ref. 230K2: "Funknavigation, Elektra, Sonne, Mond, Stern, Erika", J. Goldmann (Lorenz), Vorträge vor Fernmelde-Ingenieuren der Luftwaffe - Luftnachrichtenschule Halle (Saale) [Luftwaffe Signals School], February 1944, 22 pp. [file size: 25 MB]. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL 2-V/48, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230K3: "Sonne Planungen" ["Planning of Sonne sites"; mentions Sonne station Liebau, Sonne stations 12 (Warsaw) & 23, Großsonne station 32 (Danzig), and new Sonne site near Oppeln], Luftnachrichten telegram, dated 29 July 1944, signed by Capt. Franz, 1 p. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL 2-V/6, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230K4: "Consol - Beacon Direction Finding system of high accuracy" [Consol, Sonne, SBA], John E. Clegg, in "Wireless World", Vol. 52, No. 7, July 1946, pp. 233-235. Source: worldradiohistory.com, retrieved 6 January 2021.
• Ref. 230L: "Radio vs. U-boat" - An account of the part played by radio in the Battle of the Atlantic", G.M. Bennet, in "Wireless World", Vol. 52, No. 12, December 1946, pp. 408-411. Source: worldradiohistory.com, retrieved 6 January 2021.
• Ref. 230M: "Demonstrations of Radio Aids to Civil Aviation: Technical Descriptions of Radio Aids Demonstrated in the United Kingdom on Behalf of P.I.C.A.O during September 1946" [Consol, Post Office Position Indicator (POPI), Automatic DF (Radio Compass), weather radar, Gee with L & θ indicator, Decca, Rebecca Mk II & IV + Orbit Computer, VHF Omni-directional Radio Beacon(ORB), VHF Rotating Beacon, VHF Cathode Ray DF (CRDF), Airfield Control radar (ACR), SCS-51, Airfield Surface Movement Indicator (ASMI), BABS Mk II, radio altimeter slot antenna, GEE/BABS/Rebecca trainers, H2S/ASV trainers], Great Britain, Ministry of Civil Aviation, Provisional International Civil Aviation Organisation, H.M. Stationery Office, 1946, 84 pp. Source: chingchic.com, retrieved 5 January 2021. [file size: 25 MB]
• Ref. 230N: articles about VHF rotating-phase navigation systems, "UKW-Phasendrehfunkfeuer",  VOR, Erich
• Ref. 230N1: "An Omnidirectional Radio-Range System - Part I & II" [VOR], David G.C. Luck, in "RCA Review", Vol. VI, Nr. 1, July 1941, pp. 55-81, Vol. VI, Nr. 3, January 1942, pp. 344-369. Source: worldradiohistory.com, retrieved 25 October 2020.
• Ref. 230N2: "Omnirange = Air Safety", Samuel Freedman, in "Radio Electronics", February 1951, pp. 24-26. Source: worldradiohistory.com, retrieved 27 January 2021.
• Ref. 230N3: "An omnidirectional Radio Range system - Part I &Part II", D.G.C. Luck, in "RCA Review", Vol. VI, No. 1, July 1941, pp. 55-81, and Vol. VI, No. 3, January 1942, pp. 344-369. Source: worldradiohistory.com, retrieved 11 April 2021.
• Ref. 230N4: "The CAA VHF Omnirange", H.C. Hurley, S.R. Anderson, H.F. Keary, Civil Aeronautics Administration, Electronics Div., Technical Development & Evaluation Center, Technical Development Report No. 113 (CAA TDR-113), January 1949 (published June 1950), 65 pp.
• Ref. 230P: original correspondence of the Director General of Luftwaffe Signals Corps (General Nachrichtenführer). Source: Bundesarchiv file nr. (Signatur) RL 2-V/5, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230P1: "Anruf Gen.Martini wegen Erstellung Boden-Truhe West" [telephone call with General Martini regarding construction of Boden-Truhe West]. Letter/telegram from Gen. Nachrichtenführer (1.Abt.II), addressed to Chef. der Ln.Inspektion. Letter ref. OKL Gen.Nafü. Nr. 10 955/44 g.Kdos. (1. Abt.II). Letter is dated 18 June 1944. Letter states that due to current situation, the forward-looking Boden-Truhe West station will not be constructed and construction of the rearward-looking Boden-Truhe West station will be accelerated, using transmitters of the prior. The planned transmitters will be transported from France, but with trucks/lorries (wood gas) instead of by rail.
• Ref. 230P2: "Fernmündliche Rücksprache Major Kluge - Hptm. Gottschalk am 30.6.44" [telephone conversation Major Kluge - Captain Gottschalk]. Letter from Gen.Nafü (1.Abt.), addressed to Lfl.Kdo. 3 - Höh.Nafü, General der Navigation, and General der Kampfflieger. Letter ref. OKL Gen.Nafü. Nr. 11 092/44 g.Kdos. (1. Abt.II). Letter dated 8 July 1944. Letter states that, due to operational and test reasons, construction of radio navigation stations "Komet 2 (Laharie)", "Komet 3 (Labouheyre), and "Dora 2 (Morlaix) cannot be finished. Due to failure of "Erika 2 (Cherbourg)", the "Erika" system can no longer be used in the West. Therefore, "Erika 1 (Boulogne)" can be dismantled and parts (transmitter etc.) be secured.
• Ref. 230P3: "Sender for Bodentruhe" [transmitters for Truhe ground station]. Letter from Gen.Nafü (1.Abt.), addressed to Gen.Nafü/Ln.Insp (5.Abt/6.Abt). Letter is dated 8 July 1944. Letter describes allocation of 3 "Feuerstein" transmitters instead of "Feuerzange" transmitters to "Bodentruhe West", also mentions 3 "Merkur" transmitters are to be modified for "Bodentruhe West", schedule for delivery of additional "Merkur" and "Feuerstein" transmitters to be provided.
• Ref. 230P4: "Abschalten von Rundfunksendern." [Shutdown of (public) radio broadcast transmitters]. Letter from OKL.Gen.Nachrichtenführer. Letter ref. 11 987/44 geh. (1.Abt.II). Letter is dated 2 July 1944. Letter states that, as agreed with OKW and RPromin [Reichs Propaganda Ministerium], the request for shutting down radio broadcast transmitters during jamming/interference of radio beacons for day & night fighters, is denied. Reasons given by RPromin: 1) the current regulations already imply large scale shutdowns, further reduction is unacceptable for the propaganda, 2) the population interprets shutdowns as sign of imminent air raids. Shutdown for other reasons would cause unrest, and 3) Broadcast transmitter frequencies are fixed. If broadcast transmitters interfere with radio beacons or other services, Lfl.Kdo. must make sure that those services use other frequencies. As in other Luftflotten regions, restriction of radio beacons improves spread of utilized frequencies.
• Ref. 230Q: articles about Knickebein
• Ref. 230Q1: "Location of Knickebein stations K1-K13" [map coordinates, satellite images, aerial photos], Frank Dörenberg, latest update: 27 March 2022, 22 pp.
• Ref. 230Q2: pp. 245-247 in "Gleichgeschaltet: Maulburg im Nationalsozialismus und die Rolle von Hermann Burte im Dritten Reich", Hansjörg Noe, Verlag Waldemar Lutz (publ.), 448 pp., ISBN 978-3-922107-09-5. [Extract]
• Ref. 230Q3: p. 16 of "Knickebein" thread in the forum of geschichtsspuren.de, post by ChristianCH on 30-Mar-2014. [Extract]
• Ref. 230Q4: p. 2, 3 in "Krigsminner 1940-45 i Klepp kommune" ["War memories 1940-45 in the Klepp municipality"], F. Ravndal, T. Ødemotland, A. Jakobsen, T. Erga, O. Håland, B. Bore, A. Hatteland, J. Sørbø, T. Reve, Laget (publ.), 1990, 8 pp. Source: Norwegian National Library, accessed 31 July 2020. [pdf]
• Ref. 230Q5: "Kontrollpunkten der Knickebein-Anlage 4 (Karten), dabei Gesamtübersicht der Kontrollpunkte, Bereich zwischen Kranenburg und Donsbrüggen" [file size: 34 MB] ["Radiation-pattern check points for Knickebein Nr. 4 ( = Kleve-Materborn) in the area between Kranenburg and Donsbrüggen"], 8 maps with check points marked by small red dots and red lines, some measured field strength values are written in green (dated January 1942), Kranenburg = ca. 13 km west of K4; Donsbrüggen = ca. 12 km northwest of K-4; 2 maps with check points in The Netherlands (just north & south of Groesbeek = ca. 18 km west of K-4)]. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL 19/6/64 - 19/6/84 (frmr. RL 19/537), used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230Q6: "Knickebein" [incl. difference between KG 100 and other LW Kampfverbände], Luftwaffenführungsstab Ia (KM), adressed to "I L", 6 October 1940, g.Kdos, 1 page + 1 map. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RM 7/2372, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230Q7: "Navigatorische Ausnutzung von Fernfunkfeuern Ukw. (Knickebein)" ["Utilization for navigation of long-range VHF radio beacons (Knickebein)"], memo Az. 47 p 14, B.Nr. 545/40 g.Kdos., signed by Major Schubert for the Chief of Staff of Luftflottenkommando 2, 5 May 1940, 3 pp. [Keywords: Knickebein, coordinates / radio frequency / center beam pointing direction for Stolberg & Kleve, width of the dots & dashes zones, vertical extent of the radiation pattern, 2 pp. utilization guidelines "Merkblatt" - not to be taken into the aircraft; if taken prisoner, no information shall be divulged]. Source: Bundesarchiv (BArch) Freiburg/Germany, Signatur/file nr. RL 19-6/40 (frmr. RL 19/537), low quality microfiche, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230Q8: "Planung und Erstellung von UKW-Fernfunkfeuern (FFuFd) für die Funknavigation der Luftwaffe" ["Planning for, and construction of, long-range VHF radio navigation beacons of the Luftwaffe"], memo Az. 47 f 68, Nr. 2714/39 g.Kdos., addressed to Reichsminister of Aviation, Supreme Commander of the Luftwaffe, and Chief of the Signal Corps; draft signed by Flight Staff Engineer Gosewisch, 10 September 1939, 12 pp. [Keywords: high priority construction of beacons for Luftwaffe operations over the North Sea; requirements for the first 5 rotable beacons (3x Telefunken G.m.b.H. (high power (3 kW); up to 1200 km range (depending on radio set and aircraft altitude); to be located at Stolberg, Cleve, Borkum; code name Knickebein; antenna system weight ca. 200 metric tons), 2x C. Lorenz A.G. (lower power (500 W); up to 300-600 km range; to be located at Bad St. Peter and on the isle of Sylt; code name Karussel) in terms of equisignal beam width ±0.2° initially (later ±0.1°), dots & dashes zones width ±12°, rotability range ±45° from center beam-direction, radio frequencies compatible with FuBl 1 radio set (29.8-33.6 MHz, 5 fixed frequencies`+ 2 field-modifiable); degree to which the terrain around the beacons must be flat and unobstructed; remote monitoring radio receiver at each site; diagram with dimensions of the Knickebein antenna system and the rotation tracks; table for standard landing beam + Knickebein + Karussel with (humidity dependent) ranges for 3 receiver types (each with 2 different antennas); graph with 0.3° equisignal beam-width and useable altitude vs. range based on beacon signals audibility = vertical usability boundaries of the equisignal beam lobe].  [file size: 25 MB]. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL 19-6/40 (frmr. RL 19/537), low quality microfiche, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230Q9: "Geodätische und elektrische Einmessung der Knickebein-Anlage - Richtlinien über die geodätische und elektrische Einmessung der Knickebein-Anlagen - Anforderungen für die Auswahl und Vermessung des Kontrollbogens bei Knickebein-Anlagen" ["Geodetic and electrical calibration of the Knickebein stations - Guidelines fo the calibration - Requirements for the selection and measurement of the verification-arc of Knickebein installations"], As. 47 f 57 Nr. 72/41 g.Kdos., draft signed by Flight Staff Engineer Gosewich, 17 January 1941, 9 pp. [Keywords: all measurement points to be marked with concrete marker (graphic), 0.5° spacing between adjacent markers, 1:5000 maps for Knickebein K-2, sample data sheet for measurements of both dots & dashes beams )]. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL 19-6/40 (frmr. RL 19/537), low quality microfiche, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230Q10: "Erläuterungsbericht zu dem Vermessungsarbeiten für den U.K.W.B Kleve - Ergänzung zum Eläuterungsberiche" ["Explanatory report regarding the measurement activities for the Kleve VHF beacon + supplement"; measurement points must have visual contact with the beacon, distance from beacon: measurement with a truck, so measurement points must lie on accessible roads; min & max distance from beacon: 0.8 and 2 km (exceptions possible); no check points allowed near power lines; check point spacing 0.5°; check points marked with marker stone, sign, or nothing; check points also to be marked on the outer concrete ring of the beacon; mentions map in ref. 230Q5], signed by Dip.-Ing Schmitt, 7 pp. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL 19-6/40 (frmr. RL 19/537), low quality microfiche, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230R: articles about the X-Verfahren ("X-Procedure), X-Gerät ("X-Equipment"), Y-Verfahren ("Y-Procedure"), Y-Gerät ("Y-Equipment"); this Y-navigation method is not to be confused with the "Y" fighter-guidance method (incl. Y-Peiler ("Y-D/F system") which is also referred to as "Y-verfahren", nor with the British radio monitoring/intercept Y-Service.
• Ref. 230R1: pp. 48-49 (X-Gerät, Y-Gerät) in "German Radio Communication Equipment", US War Department Technical Manual, TME 11-227, June 1944, 61 pp.
• Ref. 230R2: "Fliegerhorst Köthen" ["Köthen airfield"], source: Militärhistorisches Museum Anhalt, accessed 11 August 2020. [pdf]
• Ref. 230R3: pp. 14-27 in "The First Pathfinders - The Operational History of Kampfgruppe 100, 1939-1941", Kenneth Wakefield, William Kimber (publ.), 1981, 265 pp.
• Ref. 230R4: pp. lxx-lxxiv in "The Bombing War: Europe, 1939-1945", Richard Overy, Penguin Books Ltd. (publ.), 2014, 852 pp. (published 2013 by Allan Lane, published 2015 as "The Bombers and the Bombed: Allied Air War Over Europe, 1940–1945")
• Ref. 230R5: "Der gezielte Blind-Bomben-Wurf - Die deutsche Lösungen: Das X-verfahren, Das Y-verfahren (Kampf)" ["The targeted blind bomb drop - The German solutions: the X-Procedure, the Y-procedure"], Heinrich Pusch (Oberst a.D. (Colonel, retired); Gruppenkommandeur Kampfgruppe 100 in 1939, Kommandeur Luftnachrichten-Regiment 31 in 1941 and Ln-Regiment 56 in 1943], date unknown (but after 1949/50, based on references to volumes of Winston Chruchill's memoires published in 1949 & 1950, see ref. 230R14 & 230R15 below), 71 pp. [file size: 57 MB; a good-but-lower resoluton file is here 16 MB]. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. ZA 3/402a, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230R6: "The Wizard War", Chapter XIX (pp. 337-352) in "Alone", Book II in "Their Finest Hour" [file size: 29 MB], Vol. II (of 6) of "The Second World War", Winston S. Churchill, Houghton Mifflin Co. (publ.), 1949, 836 pp. Source: readerssection.com, accessed 30 December 2021.
• Ref. 230R7: "The offensive in the Aether", Chapter XVI (pp. 248-259) in "The Onslaught of Japan", Book I in "The Hinge of Fate" [file size: 23 MB], Vol. IV (of 6) of "The Second World War", Winston S. Churchill, Houghton Mifflin Co. (publ.),1950, 476 pp. Source: readerssection.com, accessed 30 December 2021
• Ref. 230R8: "Das Y-verfahren. Eine Weiterentwicklung des X-Verfahrens. Erdacht von Dr. Ing. Hans Plendl, 1940 Flieger-Oberstabingenieur bei der Erprobungsstelle der Luftwaffe Rechlin/Mecklb." ["The Y-Procedure. An evolution of the X-Procedure. Conceived by Hans Plendl, 1940, Pilot – Senior Staff Engineer at the Luftwaffe test center at Rechlin/Mecklenburg"], 32 pp. Source: Bundesarchiv (BArch) Freiburg/Germany (Signatur) file nr. ZA 3/402a, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230R9: "I./K.G.66 - Kurzer Abriss der technischen und taktischen Einsatzgrundlagen der I./K.G.66 (Zielfindergruppe West) in verschiedenen Kriegsphasen" ["Short overview of technical and tactical operationprinciples of No. 1 Group of Kampfgeschwader 66 (Pathfinder Group West)"], [keywords: target finding & marking; Ju-88 S, Ju-188 E; Vannes, Poix, Le Bourget; I./K.G.100; X-Verfahren, Y-Verfahren, Egon, 1324/Truhe-Verfahren; detailed list of I./K.G.66 aircraft/crew losses 30-May-1943 - 11-Apr-1945], Hans Herbestreit, ca. 1970, 14 pp. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL 10/638, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 230S: articles about "Komet" ("Comet")
• Ref. 230S1: "Tysk Retningsantenneanlæge i Kølby Vest for Nibe" ["German Directional Antenna Installation in Kølby, west of Nibe"; rotating-beam system "Komet" ????], Commission for the Inspection of German Radio Stations Constructed in Denmark, report by Capt. Bahnsen and Prof. Jørgen Rybner of site visit on 12 Dec 1945, 3 pp. Courtesy M. Svejgaard, used with permission. English translation by me is here.
• Ref. 230T: "Scientific Intelligence", R.V. Jones, 12 February 1947 lecture, "CIA Studies in Intelligence" Vol. 6, No. 3 (Summer 1962), pp. 55-76. Source: cia.org, accessed 12 August 2020. This is a slighly edited version of the original 12 February 1947 lecture, as first published in "Journal of the Royal United Services Institution", nr. 42, August 1947, pp. 352-360.
• Ref. 230U: "Graphic survey of radio and radar equipment used by the Army Air Force", U.S. Army Air Forces, Air Technical Service Command
• Ref. 230U1: Section one, "Countermeasures equipment", 1 February 1945, 89 pp.
• Ref. 230U2: Section three, "Radio navigation equipment", 1 May 1945, 68 pp. [file size: 21 MB]
• Ref. 230U3: Section four, "Radar navigation equipment", 1 July 1945, 138 pp.
• Ref. 230V: "Navigational Aids" [MF & HF D/F, SBA, Radio Ranges, Gee, SCR 277, B/T, BABS, GCA], pp. 24-28 in "The signals war: A brief history of no. 26 Group", AIR 14/3562, UK Air Ministry, Bomber Command, December 1945.
• Ref. 230W: "Aerial Navigation and Traffic Control with Navaglobe, Navar, Navaglide, and Navascreen", H. Busignies, Paul R. Adams, Robert I. Colin, in "Electrical Communication - A Journal of Progress in the Telephone, Telegraph and Radio Art", published by "International Standard Electric Corp.", Vol. 23, No. 2, June 1946, pp. 113-143. Source: worldradiohistory.com, retrieved 17 August 2020.
• Ref. 230Y: "Radionavigation in the UK in World War II", F.C. Richardson, in "The Journal of Navigation", Vol. 45, Issue 1, January 1992, pp. 60-69. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 230Z: "Zielfluggeräte nach ‟Dieckmann-Hell‟" [Dieckmann-Hell airplane radio direction finding systems; Luftwaffe ZVG 15 / 16 / 17 Z, FuG 141], Werner Thote, in "Radiobote", Vol. 13, Nr. 76, September-October 2018, pp. 14-19. Source: radiobote.at.
• Ref. 234: general articles about aviation in Germany through WW2
• Ref. 234A: "Die Flugsicherung in Deutschland vor 1945 - Ein Rückblick" ["Air traffic control and air navigation in Germany before 1945 - a review"], Vol. 1 of "Entwicklung der Flugsicherung in Deutschland" ["Development of air traffic control in Germany"], Frank W. Fischer, International Advisory Group Air Navigation Services (ANSA, self publ.), 2014, 464 pp. [key words incl. blind landing with infrared light, accoustic signal, and the Lorenz system]
• pp. 252, 253, 256-258, 260, 261 from "Funknavigationssysteme" ["Radio navigation systems"], Appendix F (pp. 252-263) to Chapter 4 "Die Entwicklung in den 1920'er, 1930'er und 1940'er Jahren"
• Ref. 234B: "German Commercial Air Transport until 1945", Liudger Dienel, Martin Schiefelbusch, in "Revue belge de philologie et d'histoire – Belgisch Tijdschrift voor Filologie en Geschiedenis", vol. 78, nr. 3-4, 2000, pp. 945-967. [pdf]
• Ref. 235: "blind" landing systems, instrument landing systems, Ground Controlled Approach (GCA)
• Ref. 235A: "Schlechtwetterlandeanlagen" ["Bad-weather landing systems"], Telefunken commercial brochure W.B.160D (2000), 1936 (?), 4 pp. Source: www.cdvandt.org.
• Ref. 235B: installations at various airports
• Ref. 235B1: "20 Jahre Funkstation Dübendorf 1919–1939" ["20 years airport radio station of Dübendorf/Switzerland"], Max Unterfinger, Josef Baumgartner, unpublished typescript, 1939, 472 pp. The referenced photos were published in "Ein Beitrag zur Flugsicherungs Geschichte" ["A contribution about air traffic control history"; ZZ, RDF, Lorenz SBA, FuG-100 & AN/APN-1 radalt, PAR, ILS], Hans H. Jucker, July 2014, 61 pp. Source: www.wrd.ch. Retrieved 18 May 2020.
• Ref. 235B2: pp. 40, 43, 45, 48, 54 in "Gatwick: The Evolution of an Airport" [file size: 21 MB], John King, Issue No. 16 of "Sussex Industrial History - Journal of the Sussex Industrial Archeology Society", 1986, 74 pp. Source: docplayer.net, accessed 24 September 2020.
• Ref. 235B3: pp. 43-45 in "Croydon - Britain's Liverpool of the Air", chapter 2, pp. 29-45 in "European skyways; the story of a tour of Europe by airplane", Lowell Thomas, Boston Houghton Mifflin Co. (publ.), 1927, 524 pp. Source: hathitrust.org, retrieved 9 October 2020.
• Ref. 235B4: in "Engineering, an illustrated weekly journal", 25 December 1936, p. 703.
• Ref. 235B5: "Grande Bretagne" ["Great Britain"] in "Les aviation étrangers" ["Foreign aircraft"] column in "Les Ailes", Vol. 16, No. 780, 28 May 1936, p. 8. Source: Bibliothèque nationale de France, accessed 20 January 2022.
• Ref. 235C: articles of the Institute of Radio Engineers (IRE) -  "Proceedings of the IRE" and "IRE Transactions on Aeronautical and Navigational Electronics" (ANE). Source "Proc. of the IRE": worldradiohistory.com, retrieved June 2014 - May 2020.
• Ref. 235C1: "Report on Experiments with Electric Waves of about 3 Meters: Their Propagation and Use", Abraham Esau, Walter M. Hahnemann, in "Proc. of the I.R.E.", Vol. 18, Issue 3, March 1930, pp. 471-489. [Abstract].
• Ref. 235C2: "A new field application for ultra-short waves", Ernst Kramar, in "Proc. of the IRE", Vol. 21, Nr. 11, November 1933, pp. 1591-1531.
• Ref. 235C3: "The present state in the art of blind landing of airplanes using ultra-short waves in Europe" [1934/35, 33 MHz LOC, 38 MHz markers], Ernst Kramar, in "Proc. of the I.R.E.", Vol. 23, Nr. 10, October 1935, pp. 1171-1182. [Abstract]
• Ref. 235C4: "A Radio Beacon and Receiving System for Blind Landing of Aircraft", H. Diamond, F.W. Dunmore, in "Proc. of the I.R.E.", Vol. 19, Nr. 14, April 1931, pp. 585-626. [Abstract]. NOTE: this is an expanded version of ref. 235Y4 below.
• Ref. 235C5: "A new system for blind landing of aircraft" [VHF (345 MHz) CW transmitter horizontal dipole antenna in aircraft, directional receiving system on ground (2 crossing loop antennas with "equi" direction aligned with runway center line). Long-wave (350 kHz) AM transmitter on ground transmits Localizer deviation (modulation depth) to aircraft], K. Baumann, A. Ettinger, in "Proc. of the I.R.E.", Vol. 24, Nr. 5, May 1936, pp. 751-754.
• Ref. 235C6: "Coupled Networks in Radio-Frequency Circuits" [transmission-line bridge with coupled TL-section, as used in AAC LOC system], Andrew Alford, in "Proc. of the I.R.E.", Vol. 29, Nr. 2, February 1941, pp. 55-70.
• Ref. 235C7: "Instrument Landing at the National Bureau of Standards", Frank G. Kears, in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp. 61-67 [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C8: "Operational Flight Testing of Early Instrument Landing Systems", E.A. Cutrell, in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp. 67-70 [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C9: "Ground-Controlled Approach---Its Development and Early Operational Use", Chester Porterfield, in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp. 71-75, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C10: "All-Weather Landing", J.L. Anast, in "IRE Trans. on ANE", Vol. 1, Issue 2, June 1959, pp. 75-77, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C11: "A Survey of Instrument Approach Systems in the United States", Henry L. Metz, in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp. 78-84, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C12: "Improvements on the Instrument Landing System", in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp.85-94, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C13: "Electronic Landing Aids for Carrier Aircraft", A. Brodzinsky, in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp. 95-99, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C14: "Glide-Slope Antenna Arrays for Use under Adverse Siting Conditions", in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp. 100-111. [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C15: "The FAA Philosophy and Program of Instrument Approach and Landing System Development", L.C. Wright, D.J. Sheftel, in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp. 112-117. [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C16: "A Look at the Future of Automatic Landing Systems", G.B. Litchford, A. Tatz, F.H. Battle, in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp. 118-128, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C17: "An Automatic Landing System", F.D. Powell, in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp. 135-142. [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C18: "The AN/MSN-3: An Automatic Ground-Controlled Approach System", H. Goldstein, B. Cutler, in "IRE Trans. on ANE", Vol. 6, Issue 2, June 1959, pp. 142-148, [Abstract]. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235C19: "Beam transmission of ultra short waves", Hidetsugu Yagi, in "Proc. of the I.R.E.", Vol. 16, No. 6, June 1928, pp. 715-741.
• Ref. 235C20: "The development of a new Station Location or Z-Marker antenna system", J.C. Hromada, in "Proc. of the IRE", Vol. 32, Nr. 8, August 1944, pp. 454-463.
• Ref. 235D: pp. 114-115 in "Sangamo in Peace and War", Part 2 of "Sangamo, a history of fifty years", Robert Carr Lanphier, Benjamin Platt Thomas, 1949, 145 pp. Source: hathitrust.org, accessed 10 September 2020.
• Ref. 235E: "Operation and Maintenance of Lorenz Equipment" and "Ultra-Short-Wave Blind-Approach System", pp. 55-64 and pp. 114-128 in "Aeroplane Radio Equipment - Dealing with Marconi, Standard, and North American radio equipment, with special notes on direction finding equipment, Lorenz equipment, and bonding and screening", Edward Molloy (ed.), Ernest Walter Knott (ed.), Vol. 17 of "Aeroplane Maintenance and Operation Series", Chemical Publishing Company, Inc. (publ.), 1941, 133 pp. Source: hathitrust.org. Retrieved 22 May 2020.
• Ref. 235F: "Schaltung und Aufbau der Sender" ["Circuit and construction of the transmitters"], Part II of "Die Sender und Sendeanlagen der Reichsflugsicherung" ["Circuits & construction of ground-station transmitters"], Vol. 3 of "Flugsicherungstechnische Lehrbücher" ["Air traffic control textbooks"], Hans-Joachim Zetzmann, Georg Siemens Verlagsbuchhandlung (publ.), 1938, 106 pp.
• Ref. 235G: "Die Ultrakurzwelle-Funkbake" ["The VHF radio beacon"; general description and method of operation of an A/N approach guide-beam beacon], E. Kramar, in "Elektrische Nachrichten-Technik (E.N.T.)", Vol. 9, Nr. 12, December 1932, pp. 469-473. Source: cdvandt.org.
• Ref. 235H: articles in "Air Corps News Letter" (source: Air Force Historical Support Division), "Air Force", and "Air Force Magazine" (source: airforcemag.com):
• Ref. 235H1: "First solo blind flight a success" [Hegenberger, localizer + marker beacon], Joseph S Edgerton, in "Air Corps News Letter", Vol. XVI, No. 6, 28 May 1932, pp. 4-5, retrieved 6 September 2020.
• Ref. 235H2: "Collier Trophy presented to Captain Hegenberger", in "Air Corps News Letter", Vol. XVIII, No. 14, 1 August 1935, pp. 4-5.
• Ref. 235H3: "Flying Blind" [Doolittle 1929 flight], C.V. Glines, in "Air Force Magazine", September 1989, pp. 140-141, retrieved August 2020.
• Ref. 235H4: "Shooting landings by radio", F.L. Moseley, in "Air Force: the official journal of the U. S. Army Air Forces", Vol. 27, No. 10, October 1944, pp. 41-44.
• Ref. 235J: articles by Eric M. Conway
• Ref. 235J1: "Blind Landings - Low-Visibility Operations in American Aviation 1918-1958" [general history, why runways?, curved & straight glide path guidance, leader-cable system, SCS-51], Erik M. Conway, The Johns Hopkins University Press (publ.), 2006, 235 pp. Retrieved 2 February 2020 [pdf]
• Ref. 235J2: "The Politics of Blind Landing", Erik M. Conway, in "Technology and Culture", Vol. 42, No. 1, January 2001, pp. 81-106. Source: jstor.com, accessed 23 August 2020. [pdf]
• Ref. 235K: "Blind flying on the beam, aeronautical communication, navigation and surveillance: its origins and the politics of technology". Source: NASA Technical Reports Server (NTRS), retrieved 13 January 2020.
• Ref. 235K1: "Part one: Form and Function", Randy Johnson, in "Journal of Air Transportation", Vol. 8, No. 1, 2003, pp. 37-68
• Ref. 235K2: "Part II: "Political Oversight and Promotion", Randy Johnson, in "Journal of Air Transportation", Vol. 8, No. 2, 2003, pp. 57-78
• Ref. 235K3: "Part III: Emerging Technologies, The Radio Range - The Radio Beacon and Visual Indicator", Randy Johnson, in "Journal of Air Transportation", Vol. 8, No. 2, 2003, pp. 79-104
• Ref. 235L: articles in "Journal of the IEE, Part IIIA: Radiocommunication"
• Ref. 235L1: "The development of c.w. radio navigation aids, with particular reference to long-range operation”, R. V. Whelpton, P. G. Redgment, in Vol. 94, Issue: 11, March-April 1947, p. 244-254. [Abstract]
• Ref. 235L2: "C.W. Radio Aids to Homing and Blind Approach of Naval Aircraft", D. Quinn, R.D. Holland, in "J. of the IEE, Part IIIA: Radiocommunication", in Vol. 94, Issue 16, March-April 1947, pp. 953-960.
• Ref. 235L3: "C.W. Radio Aids to Approach and Landing", M. Birchall, in Vol. 94, Issue 16, March-April 1947pp. 943-952
• Ref. 235L4: "Discussion on "C.W. Navigational Aids" at the Radiocommunication Convention, 2^nd April 1947", in Vol. 94, Issue 16, March-April 1947pp. 1022-1028.
• Ref. 235L5: "Discussion on "C.W. Navigational Aids" - The Author's Replies to the Above Discussion", in Vol. 94, Issue 16, March-April 1947pp. 1029-1030.
• Ref. 235M: articles about approach and landing procedures (ZZ (QGX), Controlled Descent through Cloud (CDTC), Jägerlandeverfahren, Hegenberger, ...)
• Ref. 235M1: "Um die Sicherheit des Luftverkehrs - Nebel, Vereisung, Schlechtwetter und ihre Überwindung" [incl. ZZ-Verfahren], Kurt W. Streit, in "Prisma : illustrierte Monatsschrift für Natur, Forschung und Technik", Vol. 5, nr. 12, April 1951, pp. 539-545. Source: e-peridodica.ch, retrieved 4 May 2021.
• Ref. 235N: "The Search for an Instrument Landing System, 1918-1948", William M. Leary, Chapter 3, pp. 80-99 in "Innovation and the Development of Flight", Roger D. Launius (ed.), Texas A&M University Press (publ.), 1^st ed., 1999, 335 pp. [pdf]
• Ref. 235P: articles in (popular) radio and aviation magazines, primarily 1930s
• Ref. 235P1: "Flying the Radio Beam", Henry W. Roberts, in "Short Wave Craft", February 1936, pp. 582, 583, 624, 625. Source: worldradiohistory.com, retrieved 28 February 2020.
• Ref. 235P2: "The "Air-Track" System of "Blind Landing"", Charles E. Planck, in "Radio-Craft", Vol. IX, Nr. 4, April 1937, pp. 202, 248, 255. Source: worldradiohistory.com, retrieved 1-July-2020.
• Ref. 235P3: "The Lorenz Blind Landing System", Roderick Denman, in "The Wireless World - The Practical Radio Journal", Vol. XXXVI, Nr. 14, Nr. 814, 5 April 1935, pp. 332-335. Source: worldradiohistory.com. Accessed 21 July 2020.
• Ref. 235P4: "Landing aircraft by sound - a demonstration of the Lorenz Blind Landing System" [Lorenz installation at Heston airport, demo flight with British Continental Airways airplane], in "The Wireless World - The Practical Radio Journal", Vol. XXXVIII, Nr. 26, Nr. 878, 26 June 1936, p. 627. Source: worldradiohistory.com. Accessed 21 July 2020.
• Ref. 235P5: "Radio Aloft", John B. Brennan, in "Radio News", Vol. XIV, Nr. 3, September 1932, pp. 140-141. Source: worldradiohistory.com, accessed 22 July 2020.
• Ref. 235P6: "Air traffic control", in "Wonders of World Aviation", Vol. 1, Part 7, 19 April 1938. Source: wondersofworldaviation.com, accessed 18 August 2020.
• Ref. 235P7: "Down the beam - an amateur tries Heston's Blind Approach System : Technique which requires only practice", H.A. Taylor, pp. 648-649 in "Flight" ["Flight International" since 1962], 18 June 1936.
• Ref. 235P8: "Instrument Landing System for Aircraft - Part I", Henry W. Roberts, in "Aero Digest including Aviation Engineering", Vol. 29, Nr. 10, October 1936, pp. 43-46. Source: library.upenn.edu, retrieved May/July 2020.
• Ref. 235P9: "Instrument Landing System for Aircraft - Part II" [Lorenz blind landing system, burried cable systems (Loth, Simon)], Henry W. Roberts, in "Aero Digest including Aviation Engineering", Vol. 29, Nr, 11, November 1936, pp. 32-36. Source: library.upenn.edu, retrieved May/July 2020.
• Ref. 235P10: "The W.I.T. "Air-Track" System of Instrument Landing" [W.I.T. = Washington Institute of Technology], Henry W. Roberts, "Aero Digest including Aviation Engineering", Vol. 30, Nr. 4, April 1937, pp. 60, 64. Source: library.upenn.edu, retrieved May/July 2020.
• Ref. 235P11: "Lorenz B-L System" [B-L = Blind Landing], in "Aero Digest including Aviation Engineering", Vol. 30, Nr. 6, June 1937, p. 66. Source: library.upenn.edu, retrieved May/July 2020.
• Ref. 235P12: "Lorenz Blind Approach Receivers", advertising by Smith's Aircraft Instruments Ltd., in "Flight", November 1936.
• Ref. 235P13: "Lorenz Blind Approach Receivers", advertising by Smith's Aircraft Instruments Ltd., in "The Aeroplane", 13 January 1937.
• Ref. 235P14: "On the Beam: an explanation of "Standard" Beam Approach - a radio aid for landing aircraft in conditions of poor visibility" (Part 1 & 2) [SBA, Lorenz MCW system, T.U. 3 main LOC beacon, M.U. 3 marker beacons, receiver set, RAF], Frank Preston, in "Practical Wireless", Vol. 22, No. 474, December 1945, pp. 4-9 and Vol. 22, No. 475, January 1946, pp. 50-51. Source: worldradiohistory.com. Accessed 25 August 2020.
• Ref. 235P15: "Radio Landing Systems" [MIT GCA, Lorenz, Lorenz/ITT SBA, SCS-51], P.R. Darrington, in "Wireless World", April 1978, pp. 38-43, 56. Source: worldradiohistory.com, retrieved 20 August 2020.
• Ref. 235P16: "Radio method of blind landing" [Hegenberger, US Army Air Corps, localizer + marker beacon, sonic altimeter], in "Popular Aviation", Vol. 14, No. 3, March 1934, pp. 155-156, 192-193.
• Ref. 235P17: "Weston Aircraft Instruments", Blind Approach Indicator advertising by Sangamo Weston Ltd, 1945-1946.
• Ref. 235P18: "Lorenz Blind Approach Receivers", advertising by Smith's Aircraft Instruments Ltd, as distributor of Standard Radio equipment, 1937.
• Ref. 235P19: "The Problems of Blind Landing", H. C. Pritchard, in "Journal of the Royal Aeronautical Society", Issue 432, Vol. 50, Nr. 12, December 1946, pp. 935-958, with "Discussion" on pp. 958-973. Source: en.booksc.org, retrieved 12 June 201. [Summary]
• Ref. 235P20: "Link Trainer: The infamous "blue box" - history's most prolific flight simulator", pp. 70-71 in "Aeroplane", Issue No. 567, Vol. 48, No. 7, July 2020, pp. 70-71.
• Ref. 235P21: "Fluglandetechnik" [instrument landing], Karl Durst, pp. 102-107 in "Radio-Rundschau - Technisch-wirtschaftliche Zeitschrift", Vol. 1, Nr. 6, September 1946. Source: archive.org, retrieved 15 May 2020.
• Ref. 235P22: "Radiolandingsbakens, Part I - XVI" ["Radio landing beacons", in Dutch language, file size: 21 MB], in "Radio Bulletin", Vol. 18, No. 7-12 (July 1949, pp. 221-224, 246; August 1949, pp. 267-270; September 1949, pp. 304-307, 309; October 1949, pp. 339-342, 355; November 1949, pp. 380-384, 398; December 1949, pp. 440-443, 453), Vol. 19, No. 1-8, 10, 11 (January 1950, pp. 26-29; February 1950, pp. 66-68; March 1950, pp. 105-108; April 1950, pp. 135-137; May 1950, pp. 183-187; June 1950, pp. 209-211, 229; July 1950, pp. 245-248; August 1950, pp. 279-281; October 1950, pp. 351-354, 365; November 1950, pp. 339-402). Source: nvhrbiblio.nl, retrieved 30 September 2020.
• Ref. 235P23: "Latest Type AAF Blind Landing Equipment" [ITT Federal, Indianapolis system, LOC AN/MRN-1, MC-528, GS pattern], M.E. Montgomery, in "Electronic Industries", January 1945, pp. 100-103, 190, 192, 194, 196, 198. Source: worldradiohistory.com, retrieved 4 October 2020.
• Ref. 235P24: "New UHF landing system at Laguardia", in "Electronic Industries", January 1943, pp. 62-64, 107, 108.
• Ref. 235P25: "Happy Landings in Fog", Julian Legget, in "Popular Mechanics", Vol. 59, No. 6, June 1933, pp. 973-975.
• Ref. 235P26: "Lorenz-ultra-korte golf-landingsbaken voor vliegtuigen" ["Lorenz VHF landing beacon for airplanes", in Dutch], H. Veenstra, in "Radio-Nieuws", Vol. 18, No. 3, 15 May 1935, pp. 49-61. Source: nvhrbiblio.nl, retrieved 14 October 2020.
• Ref. 235P27: "IL at ID - The latest demonstration of instrument landing (IL) equipment, the Lorenz system at Indianapolis (ID)", Donald G. Fink, in "Aviation", July 1937, pp. 20, 21, 72, 75. Source: archive.org, retrieved 14 October 2020.
• Ref. 235P28: "La T.S.F." [Télégraphie sans Fil, i.e., "radio" application to aviation; incl. Lorenz landing beacon & associated cockpit instrument], L. Portier, in "Potentiel Aérien Mondial", special 1936 issue for the 15^th "Salon de l'Aéronautique à Paris" of "L'Aérophile", pp. 63-69. Source: Bibliothèque nationale de France (BnF); public domain.
• Ref. 235P29: "Landing on a radio beam", Greg Grant, in "Electronics World + Wireless World", February 1991, pp. 121-124. Source: worldradiohistory.com, retrieved 19 October 2020.
• Ref. 235P30: "The CAA Instrument Landing System - Part I & II", Peter Caporale, in "Electronics", Vol. 18, February 1945, pp. 116-124, March 1945, pp. 128-135. Source: worldradiohistory.com, retrieved 25 October 2020.
• Ref. 235P31: "Landing of aircraft in fog by radio - installation at Newark Airport", H. Diamond, in "Electronics", Vol. 4, No. 6, June 1933, pp.158-161. Source: worldradiohistory.com, retrieved 25 October 2020.
• Ref. 235P32: "40-cm waves for aviation" [MIT 700 MHz localizer beam system], in "Electronics", Vol. 9, No. 11, November 1939, pp. 12-15. Source: worldradiohistory.com, retrieved 25 October 2020.
• Ref. 235P33: "Cathode-Ray Tube used as aircraft instrument indicator" [first integrated CRT-based electronic display: ILS LO/GS deviations or altimeter, artificial horizon, directional gyro, airspeed indicator], in "Electronics", Vol. 10, Nr. 3, March 1940, pp. 36-38. Source: worldradiohistory.com, retrieved 25 October 2020.
• Ref. 235P34: "All-weather flying" [CAA landing system, Omni Ranges, DME, radar, automatic landing], in "Electronics", Vol. 16, Nr. 9, September 1946, pp. 84-87. Source: worldradiohistory.com, retrieved 25 October 2020.
• Ref. 235P35: "Air navigation by wireless - The work of the radio beacons" [Mitchel Field/NY, leader cable, capacity altimeter], in "Wireless World", No. 522, Vol. XXV, No. 9, 28 August 1929, pp. 196-198. Source: nvhrbiblio.nl, retrieved 14 January 2021.
• Ref. 235P36: "Ground-Controlled Approach for aircraft" [GCA], C. W. Watson, in "Electronics", Vol. 15, Nr. 11, November 1945, pp. 112-115. Source: worldradiohistory.com, retrieved 25 October 2020.
• Ref. 235P37: "GCA for Control of Commercial Aviation" [post-WW2 civil version by Gilfillan Bros. Co. of military GCA], in "Electronics", Vol. 16, Nr. 5, May 1946, pp. 160-161. Source: worldradiohistory.com, retrieved 25 October 2020.
• Ref. 235P38: "Status of VHF facilities for aviation" [VHF communication, VHF Range (Localizer), ILS glide-path, VOR], in "Electronics", Vol. 17, Nr. 10, November 1947, pp. 90-95. Source: worldradiohistory.com, retrieved 25 October 2020.
• Ref. 235P39: "Air navigation: survey of radio aids to civil navigation", M.G. Scroggie, in "Wireless World", Vol. 52, No. 11, November 1946, pp. 352-356. Source: worldradiohistory.com, retrieved 3 January 2021.
• Ref. 235P40: "Aerial navigation - radio aids to sky pilotage" [DF, B-T, goniometer, TFK Compass, neon lights, leader cable], Douglas G. Jeffrey, in "Aeronautics" [predecessor of "Popular Aviation" and "Flying Magazine"], Vol. 5, Nr. 6, December 1929, pp. 39-40, 66, 68, 70.
• Ref. 235P41: "The Present State of Development of Radio Instrument Airplane Landing Systems in this Country and Abroad", E. N. Wendell, in "Proceedings of the Radio Club of America", Vol. 15, Nr. 3, March 1938, pp. 22-29. Source: worldradiohistory.com, retrieved 1 April 2021.
• Ref. 235P42: color photo entitled "Experiments in developing instrument landing systems at the CAA Experimental Station, Indianapolis, Indiana. Equipment shown is used for the localizer and glide path", p. 86 of "Color Photography", in "Radio News", Vol. 29, No. 6, June 1943, pp. 82-97. Source: worldradiohistory.com, retrieved 1 April 2021.
• Ref. 235P43: "Instrument Approach System", Peter Caporale, in "Radio News", Vol. 29, No. 6, June 1943, pp. 121-125, 194, 197, 198. Source: worldradiohistory.com, retrieved 1 April 2021.
• Ref. 235P44: "Blind Flying" " [incl. Lorenz beacon, Hegenberger], in "Wonders of World Aviation", Part 15, 14 June 1938, pp. 401-406. Source: wondersofworldaviation.coma, accessed 29 May 2021.
• Ref. 235P45: "Marconi aerodrome approach beacon equipment, type WBD.4" [medium wave, main equi-signal beacon + 2 marker beacons, E/T keying], in "The Marconi Review", No. 66, May-August 1937, pp. 15-22. Source: worldradiohistory.com, retrieved 1 April 2021.
• Ref. 235P46: "Radar and Radar Approach Aids" [GCA], pp. 28-34 in "The signals war: A brief history of no. 26 Group", AIR 14/3562, UK Air Ministry, Bomber Command, December 1945.
• Ref. 235P47: "Blind landing" [Lorenz-IT&T demo at Indianapolis], in "Electronics", July 1937, pp. 26-27. Source: worldradiohistory.com, retrieved 12 June 2021.
• Ref. 235P48: "L'atterrissage sans visibiltié" ["Landing without visibility"], Lt. Vuillot, in "Revue du Ministère de l'air : organe de l'armée de l'air et de ses réserves", Vol. 1, no. 6, 15 June 1935, pp. 743-759. [ZZ-method, concentric leader cables, BoS System by Diamond & Dunmore with cross-pointer instrument, Lorenz E/T system 9 m wavelengh with cross-pointer instrument - end of ZZ]. Source: Bibliothèque nationale de France (BnF), accessed 20 January 2022.
• Ref. 235P49: "Le pilotage sans visibilité exterieure" ["Flying without outside visibility", pp. 354-358 in "Toute l'aviation", Edmond Blanc, 4^th ed., 1931, 494 pp. [Keywords: Rougerie simulator, Z / ZZ method origin, Lorenz method]. Source: Bibliothèque nationale de France (BnF), accessed 20 January 2022.
• Ref. 235Q: "C. Lorenz Aktiengesellschaft, Berlin-Tempelhof", pp. 172-182 in "Reichsverband der deutschen Luftfahrt-Industrie auf der Luftfahrt-Ausstellung, Stockholm, 1936" [catalog by the German aviation industry/trade association of German companies and their products exhibited at the International Aerospace Exhibition at Stockholm/Sweden, May/June 1936; ILIS 1936], 232 pp. Source: justus.ownit.nu, retrieved 31 May 2020. Catalog cover page and table of contents is here, courtesy B. Justusson.
• Ref. 235R: articles about  ILS developments at the CAA, MIT, and WIT
• Ref. 235R1: "The development of the Civil Aeronautics Authority Instrument Landing System at Indianapolis", W. E. Jackson, A. Alford, P.F. Byrne, H.B. Fischer in "Electrical Engineering", Vol. 59, Nr. 12, December 1940, pp. 849-858, and p. 1120 (discussion), [Abstract].  Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 235R2: "The CAA-MIT Microwave Instrument Landing System", E.L. Bowles, W.L. Barrow, W.M. Hall, F.D. Lewis, D.E. Kerr, in "Transactions of the American Institute of Electrical Engineers" (IAEE), Vol. 59, Issue 12, 1940, pp. 859-865. Source: booksc.org. [pdf, See note 1]
• Ref. 235R3: "The history and development of the Washington Institute of Technology" [Air-Track, ILS, College Park], Joseph M. Marzolf, 18 November 1938, 23. Source: archive.org, retrieved 3 July 2020. [Summary & introduction].
• Ref. 235S: to be allocated
• Ref. 235T: to be allocated
• Ref. 235U: reports of the Daniel Guggenheim Fund for the Promotion of Aeronautics
• Ref. 235U1: "The Full-Flight Laboratory", Chapter VII, pp. 29-32 in "The second report of the Daniel Guggenheim Fund for the Promotion of Aeronautics - 1928", January 1929, 48 pp. Source: hathitrust.org, retrieved 25 February 2021.
• Ref. 235U2: "Solving the problem of fog flying; a record of the activities of the fund's full flight laboratory to date", Daniel Guggenheim Fund for the Promotion of Aeronautics, 1929, 52 pp. Source: hathitrust.org, retrieved 21 February 2021.
• Ref. 235U3: "Equipment used in experiments to solve the problem of fog flying - A record of the instruments and experience of the Fund's Full flight Laboratory" [Doolittle's first instrument flight, aircraft equipment], The Daniel Guggenheim Fund for the Promotion of Aeronautics, Inc., March 1930, 57 pp. Source: hathitrust.org, retrieved 18 July 2020.
• Ref. 235V: articles/documents about the RAF military version of the Lorenz landing beam system
• Ref. 235V1: "Standard Beam Approach Ground Installations (F.G.R.I.5069 and T.G.R.I.5041)" [Fixed Ground Radio Installation 5069, Transportable Ground Radio Installation 5041, Transmitter types T.1122, T.1123, T.5041, T.1245], Chapter 4 in "Ground Station Equipment", Section 1 of "Radio Aids to Navigation", Part IV of "Royal Air Force Signal Manual", in Vol. I of "Air Publication 1168" (A.P. 1186, revised ed., June 1940, and AP 1186B, December 1942 / June 1943). Courtesy J. Harris, 2020.
• Ref. 235V2: "Automatic Keying device, Type 2", Chapter 6 in "Ground Station Equipment", in same Section 1 as in ref. 235V1 above, 8 pp. Courtesy J. Harris, 2020.
• Ref. 235V3: "Blind Approach Receivers, R.1124A and R.1125A" [file size: 38 MB], Chapter 7 in "Receivers", Section 3 in "Radio Aids to Navigation", in Part IV of "Royal Air Force Signal Manual" in Vol. I of "Air Publication 1168" (AP 1186), revised ed., June 1940, 55 pp. Courtesy J. Harris, 2020.
• Ref. 235V4: "Blind Approach Receivers, R.1124A and R.1125A", Chapter 7 in "Air Publication 1186", Volume II, Part IV, Section 3 "Receivers", Air Ministry, Royal Air Force Signal Manual, Dcember 1938. Source: tube.radio.com (scanned by Dave Prince VK4KD). Retrieved: November 2022. [file size: 20 MB]
• Ref. 235V5: "Blind Approach Transmitters, T.1122 & T.1123", Chapter 9 in "Air Publication 1186", Volume I, Part IV, Section 1 "Transmitters", Air Ministry, Royal Air Force Signal Manual, December 1938. Source: tube.radio.com (scanned by Dave Prince VK4KD). Retrieved: November 2022. [file size: 28 MB]
• Ref. 235V6: "Beam Approach Aircraft Equipment", chapter 18 of "Standard Notes for Wireless Mechanics", "Air Publication 1938" (A.P. 1938), Air Ministry, reprint of May 1944, 10 pp. Source: blunham.com, retrieved September 2020.
• Ref. 235V7: "Blind Approach Pilot's Handbook" [incl. Lorenz approach/landing beam system; RAF Blind Landing Development Unit at Boscombe Down], Air Publication 1751, Air Ministry, November 1939, ??? pp. An excerpt (6 text pages, 10 figure pages) is here. If you have the complete document, please contact me!
• Ref. 235V8: "The RAE contribution to all-weather landing" [SCS-51, approach lighting, ILS, BLEU], John Charnley, in "Journal of Aeronautical History", Vol. 1, Paper No. 2011/1, 21 pp; Accessed 18 July 2020. [pdf]
• Ref. 235V9: "Approach and landing aids" [Ground Controlled Approach CCA, Airfield Control Radar ACR, Rebecca, Beam Approach Beacon System, BABS, Standard Beam Approach SBA, Rebecca-Eureka, Gee let-down, equipment, procedures, diagrams], pages from an unidentifed WW2 RAF instruction document, 9 pp. Source: part 1 & part 2 - International Bomber Command Centre (IBBC) Digital Archive, University of Lincoln, available under Creative Commons Attribution-NonCommercial 4.0 license. Accessed 1 November 2022.
• Ref. 235W: articles/documents about the USAAF military version of the Lorenz landing beam system (USAAF SCS-51)
• Ref. 235W1: "Army Air Forces' Portable Instrument Landing System", Sidney Pickles, in "Electrical Communication - A Journal of Progress in the Telephone, Telegraph and Radio Art" [broadband "Alford" loop omni-antennas], published by "International Standard Electric Corp", Vol. 22, No. 4, 1945, pp. 262-294. Source: worldradiohistory.com, accessed 17 August 2020.
• Ref. 235W2: "Instrument Flying: Army Air Forces Instrument Approach System", U.S. Army Air Forces, Technical Order No. 30-100F-1, 10 November 1943, 16 pp. Source: aafcollection.info, accessed 1 September 2020.
• Ref. 235W3: "First-Hand: Development of the Instrument Landing System Glide Path" [SCS-51, CAA, Signal Corps, ITT Federal Laboratories, ITT Standard Telephone and Cable, Standard Elektrik Lorenz, 330 MHz, hyperbolic path, straight path, constant rate of descent], Leon Himmel. Source: etwh.org, retrieved 25 June 2020.
• Ref. 235W4: "Air service: radio range and SCS 51 equipment", Exchange of notes between the US Ambassador to the UK and the UK Minister of Civil Aviation, London May 8 and July 31, 1946, regarding transfer of certain WW2 air navigational and operational facilities in the UK, to the UK government. pp. 795-799 in "Treaties and Other International Agreements of the USA, 1766-1949", Vol. 12 "United Kingdom - Zanzibar". Source: US Library of Congress, retrieved 20 October 2020.
• Ref. 235W5: "Synthesis of multifunctional tactical landing system" [incl. SCS-51], G.B. Litchford, Air Force Flight Dynamics Laboratory, Air Force Systems Command, Wright-Patterson Air Force Base, Technical Report AFFDL-TR-67-188, January 1968, 201 pp. Source: dtic-mil, retrieved 29 November 2020.
• Ref. 235X: articles in "Electrical Communication - A Journal of Progress in the Telephone, Telegraph and Radio Art", published by "International Standard Electric Corp". Source: worldradiohistory.com, accessed 17 August 2020.
• Ref. 235X1: "Ultra-Short Wave Radio Landing Beam - The C. Lorenz A.G. Radio Beacon Guide Beam System", R. Elsner, E. Kramar, in Vol. 15, No. 3, January 1937, pp. 195-206.
• Ref. 235X2: "Aviation Radio" section (pp. 218-220) in "Electrical Communication in 1938", in Vol. 17, No. 3, January 1939, pp. 205-229. [Busignies' HF-DF model R.C.5; LMT transportable Adcock; NDB network in Europe, most major airports in Europe now equipped with Lorenz-system VHF ILS; similar development in USA; Australia using similar AN beacons for point-to-point navigation; Lorenz ILS type marker beacons now used along routes in US; 1936/37 experiments with by LMT resulted in improved Lorenz-localizer track and demonstrated in Feb 1938 in France and selected by AF; Western Electric Co. radio altimeter (FM, UHF)]
• Ref. 235X3: "Ultra-High Frequency Loop Antennae", A. Alford, A.G. Kandoian, in Vol. 18, No. 4, April 1940, pp. 255-265.
• Ref. 235X4: "Development of the C.A.A. Instrument Landing System at Indianapolis", Vol. 18, No. 4, April 1940, pp. 285-302.
• Ref. 235X5: "Aviation" [ITT receives order from CAA for "Indianapolis System" ILS at 6 major US cities, to be come operational mid-1941], p. 5 in "Electrical Communication in 1940", Vol. 19, No. 3, 1941, pp. 3-10.
• Ref. 235X6: "Instrument Landing System" and "Ultra High Frequency Two Course Radio Range with Sector Identification", p. 80  in "Western Hemisphere I. T. & T. System Communication: Contributions of 1942", in Vol. 21, No. 2, 1943, pp. 75-84.
• Ref. 235X7: "1938 - First installation of instrument landing equipment at three major London Airports", p. 217 in "Standard Telephones and Cables, Limited, London - 60^th Anniversary", C.W. Eve, in Vol. 21, Nr. 4, 1944, pp. 213-217.
• Ref. 235X8: "Development of Aircraft Instrument Landing Systems", H. H. Buttner, A. G. Kandoian, in Vol. 22, No. 3, 1945, pp. 179-192
• Ref. 235X9: "1937 - Awarded contract for supply of radio instrument landing equipment for the Defence Department, Australian Commonwealth", p. 324 in "Standard Telephones & Cables Pty. Ltd., Australia - 50th Anniversary", J. Clarke, in Vol. 22, No. 4, 1945, pp. 322-325.
• Ref. 235X10: "Standard Beam Approach" p. 6, 11 in "Electrical Communication: 1940-1945, War Years Review - Part I", in Vol. 23, No. 1, 1946, pp. 3-13.
• Ref. 235X11: "Landing aircraft with ground radar" [AN/MPN-1C, Luis Alvarez, Ground Controlled Approach (GCA), Precision Approach Radar (PAR)], J.S. Engel, in "Electrical Communication - Technical Journal of the International Telephone and Telegraph Corporation and Associate Companies", Vol. 24, No. 1, March 1947, pp. 72-81.
• Ref. 235Y: articles and documents from the US Department of Commerce (DoC, incl. Civil Aeronautics Authority / Administration; CAA), US National Academy of Sciences (NAS), and National Advisory Commission on Aeronautics (NACA)
• Ref. 235Y1: "Diamond-Dunmore", pp. 16-20 in "Federal Science Progress", U.S. Dept. of Commerce, Vol. 1, No. 3, April 1947.
• Ref. 235Y2: "Description and theory of Instrument Landing System", Federal Airways Manual of Operation IV-B-1-4, U.S. Dept. of Commerce, Civil Aeronautics Administration, 1st ed., 15 October 1949, 43 pp.
• Ref. 235Y3: "The CAA Radio Instrument Landing System with Simultaneous Voice", U.S. Department of Commerce, Civil Aeronautics Administration, Office of Federal Airways, Technical Development Services, 1946, 31 pp.
• Ref. 235Y4: "A radio system for blind landing of aircraft in fog", H. Diamond, F.W. Dunmore, in "Proceedings of the National Academy of Sciences [PNAS] of the Unite States of America", Vol. 16, Nr. 11, 15 November 1930, pp. 678-685. [pdf]
• Ref. 235Y5: "History of Instrument Landing System glide paths", Chapter 1 (pp. 1-20) in "An Airport Glide-Path System Using Flush-Mount, Travelling-Wave Runway Antennas, Vol. II", Richard H. McFarland, Ohio State University Research Foundation, Report 891-2, for the FAA Aviation R&D Service (frmr. Bureau of R&D), 31 March 1961, 177 pp. Source: dtic.mil, retrieved 25 October 2020.
• Ref. 235Y6: "The development of a straight-line glide path", J.M. Lee, H.I. Metz, Civil Aeronautics Administration, U.S. Department of Commerce, Technical Development Report No. 55 (TDR55), June 1947, 34 pp. Source: hathitrust.org, retrieved 16 January 2021.
• Ref. 235Y7: "The CAA-RTCA instrument landing system - Part I: Development and installation" [low quality scan], Henry I. Metz, Civil Aeronautics Administration, U.S. Department of Commerce, Technical Development Report No. 35 (TDR 35), October 1943, 83 pp. Source: planeandtrainwrecks.com, retrieved 16 January 2021.
• Ref. 235Y8: "The CAA-RTCA instrument landing system - Part II: Tests and modifications" [low quality scan],, Henry I. Metz, Civil Aeronautics Administration, U.S. Department of Commerce, Technical Development Report No. 36 (TDR 36), October 1943, 29 pp. Source: planeandtrainwrecks.com, retrieved 16 January 2021.
• Ref. 235Y9: "Development of a VHF directional localizer - Part I (preliminary tests) & II (the monitor)", Chester B. Watts, Samuel E. Taggart, Kennard E. Voyles, CAA Technical Development & Evaluation Center, Technical Development Report No. 183 (CAA TDR 183), May 1954, 43 pp. Source: hathitrust.org, retrieved 25 October 2020.
• Ref. 235Y10: "Methods for facilitating the blind landing of airplanes", M. Heinrich Gloeckner, National Advisory Commission on Aeronautics (NACA), Technical Memorandum No. 687 (NACA-TM-687), 1 October 1932, 28 pp. Source: ntrs.nasa.gov, retrieved 19 February 2021. Translated from "Verfahren zur Erleichterung von Blindlandungen", pp. 347-355 in "Zeitschrift für Flugtechnik und Motorluftschiffahrt" (ZFM), Vol. 23, No. 12, 24 June 1932.
• Ref. 235Z: newspaper articles
• Ref. 235Z1: "Landing a 'plane "blind" - How pilots are guided by the Lorenz wireless beam", in "The Manchester Guardian", 22 January 1937, p. 12.
• Ref. 235Z2: "To test new radio beams and landing gear for planes" [blind landing system of Lorenz + Bureau of Air Commerce + Army tested at Indianapolis (no obstacles in area), Lorenz beacon & receivers], in "Moline Daily Dispatch" (Moline/IL/USA), Vol. 59, 24 April 1937, p. 11, 13.
• Ref. 235Z3: "Last word in modern safety devices being tested at Municipal Airport - Engineers expect equipment to eliminate air tragedies - Blind flying systems and "Tricycle" landing gear under severe trials" [blind landing system of Lorenz + Bureau of Air Commerce + Army tested at Indianapolis (no obstacles in area), Lorenz & receivers, E. Donovan], A.F. Casse, in "The Indianapolis Sunday Star", 25 April 1937, p. 71.
• Ref. 235Z4: "Airplanes to push blind flying" [improved Lorenz VHF system, secretly installed at Indianapolis, marker beacons; DoC experimented with it in 1932; compared to Hegenberger system at Oakland/CA], in "Des Moines Tribune", 30 April 1937, p. 10.
• Ref. 235Z5: "U. S. flyers try European "blind" landing system" [Indianapolis, demo by ITT ( = "Lorenz Low Approach" system)], Wayne Thomis, in "Chicago Daily Tribune", Vol. XCVI, No. 116C, 15 May 1937, p. 7.
• Ref. 235Z6: "Croydon airport - Front door to the world" [Lorenz, Plessey, and Marconi landing beam systems recently installed], in "Chicago Sunday Tribune", Vol. XCVII, No. 1, 2 January 1938, p. 100.
• Ref. 235Z7: "Automatic plane landing system is perfected by Army engineers" [test 2 years at Wright Field, Dayton/OH; War Dept. hand off to Bureau of Air Commerce], in "The Indianapolis Star", Vol. 36, No. 36, 11 July 1938, p. 9.
• Ref. 235Z8: "In Manchester - Ringway will defy fog" [Ringway airport, illuminated fog-line + Lorenz beacon, first outside London airports], in "The Manchester Guardian", 8 November 1938, p. 13.
• Ref. 235Z9: "Conquest of foggy landings for airplanes believed near - Novel radio control and tunnel dissipator studied in effort to bring ships safely to ground when ceiling remains at zero" [M.I.T. system, 3 lights on instrument panel, guidance by "radioed lights"; also mentions Bendix, Lorenz, Air-Track systems; chemical fog dissipators/absorbers], in "Arizona Daily Star" (Tucson/AZ), 14 January 1939, p. 5.
• Ref. 235Z10: "In Manchester - Landing by ear" [Lorenz E/T (!) aural landing beam being added], in "The Manchester Guardian", 26 July 1939, p. 11.
• Ref. 235Z11: "Blind landings" [CAA specs, A. Alford, Int'l Telephone Development Co., Bell Telephone Labs, newly selected standard system (75-112 MHz, GS + LOC), MIT "horn" system (UHF, microwave)], in "The Evening Sun" (Baltimore/MD), Vol. 60, 23 January 1940, p. 4.
• Ref. 235Z12: "Private flying in new year - Blind approach systems" [Standard Beam Approach System (Lorenz) shows no improvement over pre-war Lorenz system at Hendon], in "The Manchester Guardian", 28 December 1945, p. 2.
• Ref. 241: "Erprobungsstellen der Luftwaffe" [Luftwaffe test sites, incl. Rechlin, Süd/Foggia, Tarnewitz, Travemünde, Udetfeld, Werneuchen]. Bestandsbeschreibung [file description] of Bundesarchiv file nr. (Signatur) RL36. Retrieved 28 August 2019.
• Ref. 244: Luftwaffe & Royal Air Force fighter intercept & control methods ("Jagdverfahren"), maps, and related topics
• Ref. 244A: "Nachtjagd" [intro, descriptions, and evaluations], Luftwaffe document, date unknown, 18 pp. Source: German Russian Project for digitization of archives in the Russian Federation. Retrieved 29 August 2019.
• Ref. 244B: "Bestimmungen über Nachtjagd" [descriptions of methods, and instructions to Flak organisation regarding night fighting], 1^st Flakdivision, Berlin, 19 November 1943, 12 pp. Source: German Russian Project for digitization of archives in the Russian Federation. Retrieved 29 August 2019.
• Ref. 244C: "Mosquito Nachtjagd", [specific fighter and flak tactics against incoming British "Mosquito" fighter-bombers] 1^st Flakdivision, Berlin, 7 March 1944, 5 pp. Source: German Russian Project for digitization of archives in the Russian Federation. Retrieved 29 August 2019.
• Ref. 244D: "Das Y-verfahren für Tag- und Nachtjagd" ["The Y-Procedure for day and night fighter control (navigation method)"], document without reference number, author unknown, without date (but before May 1945), without place, 114 pp. The 1960s file coversheet of the Militärgeschichtliches Forschungsamt (Research Office for Military History) suggests that it dates to 1940/41, 114 pp. [file size: 82 MB !!!! - with reduced resolution [file size: 84 MB; good-but-lower-reslution file is here 27 MB],
• Complete description of the "Y" procedure for day & night fighter control from ground plotting stations with short wave equipment. Keywords: Y-Verfahren, Y-Führung, Y-Stelle, Y-Stellung, Y-Anlage, Y-Station, Y-Einrichtung, E 16, FuG 16, Graetz-E-Mess-Gestell, Siemens-E-Mess-Gestell, Heinrich Peiler, ZVG 16, ZE ZY Zeiger, Schildkröte, PQK, S 16.
• Source: BArch file nr. (Signatur) RL 2-V/38, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 244E: "Anlage 1 zu Luftflottenführungsabteilung Ia op2 Nr. 500/41 geh." [file size: 28 MB; good-but-lower-resolution file is here, 4 MB]. Map is not dated.
• Map covers area of Belgium, The Netherlands, Denmark, northern Germany incl. Berlin. Map is marked with locations of militärische Sperrgebiete, Nachtsperrgebiete, Nachtjagdgebiete, Dunkle Nachtjagdsräume.
• Map size: 4x2 (WxH) A4-sheets. Map is low-quality blueprint copy.
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL 20/186/K, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 244F: "Einsatzbeispiel für einen Feindeinflug" (example of response to intruding enemy aircraft). Map is not dated. [file size: 84 MB; good-but-lower-resolution file is here, 10 MB].
• Map shows ground track of enemy bomber stream arriving from Britain with target Frankfurt, intercepting fighters, timing, etc. Map includes large & detailed table of the entire nightfighter intercept process, from long-range radar detection to "kill", with step-by-step status/activity/communication at the level of Flugmeldekompanie, Nachtjagdraum, Fühlungshalter, Jagdgruppe, Flugmeldungszentrale, Fluko, and Flak; the entire sequence covers 1 hr 40 min. Map size: 4x5 (WxH) A4-sheets.
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL 36/443, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016"
• Ref. 244G: "Luft-Navigationskarte in Merkatorprojektion - Erweitertest Blatt Deutschland mit Jägernetz", Bodenorganisation Großraum-Nachtjagd Luftflotte Reich, July 1944. Source: Bestand/File 500, Findbuch/Index 12452, Akte/record 286 of the German-Russian Project for the Digitization of German Documents in Archives of the Russian Federation. Retrieved 28 August 2019.
• Ref. 244H: "Nederland en de Duitse Nachtjacht - Van jager tot prooi" (The Netherlands and German night fighting - from hunter to prey), W.H. Lutgert, R. de Winter, pp. 536- 545 in "Militaire Spectator", vol. 183, nr. 12, December 1994. Accessed September 2019. [pdf]
• Ref. 244J: "Nederland en de Duitse Nachtjacht - Van jager tot prooi (Deel 2)" (The Netherlands and German night fighting - from hunter to prey - part 2), W.H. Lutgert, R. de Winter, pp. 5-17 in "Militaire Spectator", vol. 184, nr. 1, January 1995. Accessed September 2019. [pdf]
• Ref. 244K: "De Luftwaffe en Nederland - Balans van een oorlogserfenis" (The Luftwaffe and The Netherlands - legacy of a war), W.H. Lutgert, R. de Winter, pp. 450- 459 in "Militaire Spectator", vol. 184, nr. 10, October 1995. Accessed September 2019. [pdf]
• Ref. 244L: "Nachtjagdnavigationskarte - herausgegeben von NJG.3.-NO" [night-fighter navigation chart issued by the Nachrichten-Offizier of the no. 3 night fighter-wing, Nachtjagdgeschwader 3]. [file size: 25 MB]
• Map is not dated. Bernhard-stations Be-0, Be-6, Be-8 through Be-12 are also marked on this map. Source: collection R. Grywatz.
• Ref. 244M: "Tag- und Nachtjagd, 3. Jagddivision (als beispiel)".  Map is dated 29 July 1944.  [file size: 24 MB; good-but-lower-resolution file is here, 9 MB].
• Map covers area of The Netherlands to Heilbronn/Germany. Map is marked with location of Tagjagdstellungen and Fu.M.G. sites (1., 2., and 3. Ordnung; dunajafähig vs. nicht dunajafähig).
• Map size ca 3x2 (WxH) sheets of size A4. Map scale 1:1.000.000
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL-3-1527.
• Ref. 244N: "Jagd-Einsatz im November 1943", Anlage 3 (appendix 3) to "Lfl.Kdo3, Führ.Abt(1)/1c No. 15684/43 Kdos". [file size: 19 MB]
• Large bar graph for each day of November 1943, with total number of fighter sorties for each day, split into "day" and "night" fighter. Also: table with statistics for each day: number (with type(s) of aircraft) for each type of sortie/mission: "Alarmstart" / "Überwachung und Sperre" / "Geleitschutz" / "Begleitschutz u. Augnahme"; / "Nachtjagd" (night fighter) / "Fernjagd" (long range intercept); also: total number of sorties/missions, number of enemy kills (incl. type of enemy aircraft), own losses.
• Size: size: ca. 3x3½ (WxH) A4-sheets.
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL-3-1527.
• Ref. 244P: "Abschüsse der Nachtjagd im Bereich Luftwaffenbefehlshaber Mitte", Anlage 2 (appendix 2).
• Graph with three lines: "hell" (helle Nachtjagd), "dunkel" (dunkle Nachtjagd), "kombiniert" (kombinierte Nachtjagd). Graph covers monthly statistics regarding enemy kills for the period April 1941 - March 1942.
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL-3-1527, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 244Q: "Anzahl der voll u. bedingt (ab Juli 1941) bzw. eingeschränkt (ab Mai 1943) einsatzfähigern Besatzungen" and "Anzahl der einsatzbereiten Kampf-Flugzeuge" .  [file size: 17 MB]
• Graph with monthly statistics for the period mid-1939 - mid-1939: number of available flight crews and number of operational fighter planes), separate curves for "Tagjäger" (day fighters) and "Nachtjäger" (night fighters; from late 1940 onward).
• Also: interesting large table with 53 key dates of the WW2, from 1 September 1939 (German invasion of Poland) through 15 August 1944 (anglo-american landing in southern France).
• Size: ca. 1½ x3 (WxH) A4-sheets.
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL-3-1527.
• Ref. 244R: "Fighter defence of Germany - Control of fighters by the "Y" Procedure", Samuel Denys Felkin (Chief Interrogator at Bletchley), transcribed report from the British Air Ministry, Assistant Director of Intelligence (Prisoner Interrogation), A.D.I. (K) Report No. 525/1944, 14 pp. Source: The National Archives of the UK, ref. AIR40/2875 and 2876. Retrieved from www.cdvandt.org.
• Ref. 244S: "Die Deutschen Nachtjagdverfahren" ["The German nigh fighter procedures"], Walter Grabmann, Generalmajor a.D., date unknown, 22 pp.
  [Helle Objektjagd, helle Gebietsjagd, Himmelbett, Verfolgungsnachtjagd [pursuit night], Objektjagd "Leichentuch" / "Milchglas", 1-mot Objektjagd "Wilde Sau", Fernnachtjagd [long-range night], Zusammenarbeit mit Jäger-Flak, 13 maps].
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. ZA 3/402a, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 244T: "Besprechung bei General Galland am 21.1.43" ["Meeting with Gen. Galland on 21 Jan 1943"], signed by Major Eisermann, 22 January 1943, 3 pp. [Keywords: possibility of fighter control from an aircraft carrier ("Flugzeugträger"), limitations of Freya FuMG radar for that application, proposal from Plendl to install Y-RDF system (Y-Boden-Anlage), aircraft carier to have landing beam system for fighters; the Y fighter control system (Y-Verfahren) meets its requirements but has serious practical problems due to frequency changes and exposure of the equipped lead aircraft]
• Bundesarchiv (BArch) Freiburg/Germany, Signatur/file nr. RL 16-3/12, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 245: papers about Luftwaffe transmission via radio of enemy aircraft positions.
• Ref. 245A: "Feindreportagen" ["Running commentary on enemy aircraft"] and "Bernhard-Führung" ["Bernhard guidance"], §II and §VII, respectively, in "Nachrichtenbefehl April 1945 (Nachtjagd)", 1. Jaddivision, Nafü 3 - Nr. 2600/45, 18 March 1945, 5 pp.
• Keywords: Verfolgungsnachtjagd, Führungswellen, Gruppenbefehlswellen, Geschwaderbefehlswellen UKW (Tast) Bord-Bord, Divisionsführungswellen Lgw, Kzw, UKW der 1.J.Div., Divisionsklärungswellen (Tast), Y-Linienverteilung für Aufklärer, Y-Linien für 1-mot. Nachtjagd, Mosquito-Jagd (Silber), Feindreportagen, Kennung für Fu. G 25, Rufzeichen und Rufnamen, Optische Gruppenkennung und Wellen für flg. Funkfeuer, Verschlüsselung eigener Standort- und Flughöhenangaben, Gebietsnachtjagd, Flugsicherung.
• Source: Bestand/File 500, Findbuch/Index 12476, Akte/record 90, pages 31-36 of the German-Russian Project for the Digitization of German Documents in Archives of the Russian Federation. Retrieved November 2021.
• Ref. 245B: "Funkübermittlung der feindlichen Luftlage – Auszug aus einem Bericht des Obst. Morgenstern, Chef beim Generalnachrichtenführer vom 22.3.1945" ["Radio transmission of the enemy air situation (aircraft positions) – Excerpt from a report dated 22 March 1945 of Col. Morgenstern, Chief adjoint to the lead Signal Corps General"], Gen.Nafür (1. Abt.) Nr. 11 319/45 geh., 9 pp.
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany (Signatur) file nr. ZA 3/402, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 245C: "Die Bildung der Luftlage. 1935 – 1944 (Flugmeldedienst, Funkmeßdienst, Funkaufklärung)" ["The creation of (enemy) air situation (aircraft position status). 1935 – 1944 (enemy aircraft warning service, radar service, radio intelligence service)"], Obst. A.D. Greffrath, 1946, 7 pp.
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany (Signatur) file nr. ZA 3/402, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 245D: "Die Bildung der Luftlage" ["The creation of (enemy) air situation (aircraft position status)"], Gen.Maj. a.D. Walter Grabmann, no date - possibly 1946, 10 pp.
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany (Signatur) file nr. ZA 3/402, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 247: "Air mail beacon Farmerville, Pa., Lighted by Kohler Electric Plant", cover panel of "Light for the Night Air Mail", 3 page folded sales brochure of "Kohler of Kohler - Automatic Electric Plants" of the Kohler Co. in Kohler, Wisconsin/USA. Date unknown. Source: atchistory.org. Accessed 21 July 2020.
• Ref. 252: "Rhubarb operations: Appendix V - German navigational beam stations. France, Holland and Belgium" [file size: 108 MB], AIR 40/1661, 142 pp., 1942 (with amendments made in 1942 and 1943), Air Ministry, Directorate of Intelligence and related bodies: Intelligence Reports and Papers, Deputy Director of Air Tactics. Document pages are not numbered. Item is in the collection of The National Archives; material with UK Crown Copyright, used in accordance with the Open Government License [pdf].
• Ref. 252A: "Introduction", 10 pp. A "Rhubarb" was a routine tactical operation, in which a small number of RAF aircraft flew at low-level into France or Belgium, to strafe ground targets.This particular document covers German beam stations (Knickebein, Y, X, and "Knickebeins of a new type" = Bernhard) along the Atlantic coast of France and North Sea coast of The Netherlands. Map coordinates are provided for all targets.
• Ref. 252B: "Desvres/Le Bois-Julien (Target V/18)" [ = "Bernhard" Be-3], 4 pp. (including 2 photos and 1 site/area layout map; pp. 108-111 in the complete document). Observations: circular concrete base appr. 100 ft in diameter. Hut at the center of the array. Mast some 50 ft high at 600 yards to northwest of the installation, connected by underground cable. Photos from recce sorties in March and June of 1941.
• Ref. 252C: "Sizun/St Michel (Target V/24)" [ = "Bernhard" Be-2 at Mt.-St.-Michel-de-Brasparts], 3 pp. (including 1 photo and 1 site/area layout map; pp. 134-135 in the complete document). Photo from September 1942 recce sortie. Observations: circular concrete base appr. 100 ft in diameter. Hut at the center of the array. Cable trench of ca. 950 ft in westerly direction, to short mast.
• Ref. 252D: "St. Vaast/La Pennelle (Target V/26)" [ = "Bernhard" Be-4], 4 pp. (including 2 photos and 1 site/area layout map; pp. 139-142 in the complete document). Observations: circular concrete base appr. 100 ft in diameter. Hut at the center of the array. Photos from recce sorties in April and September of 1942. Note: "La Pernelle" is misspelled as "La Pennelle".
• Ref. 252E: "Commana (Target V/1)" [ = "Y" station ?], 4 pp. Recce sortie in July of 1941.
• Ref. 252F: "La Feuillée (Target V/2)" [ = "Y" station Y8 "Friedrich"], 6 pp. Recce sortie in September of 1941.
• Ref. 252G: "Lanmeur (Target V/3)" [ = "Knickebein" station K-11], 8 pp. Recce sorties in July 1940, January & September of 1941, July of 1942.
• Ref. 252H: "Laye (Target V/4)" [ = "X" station X-#], 5 pp. Recce sorties in November of 1940 and September of 1941.
• Ref. 252J: "Beaumont-Hague (Target V/5A)" [ = "Knickebein" station K-9], 6 pp. Recce sorties in October of 1940, March & September of 1941.
• Ref. 252K: "Jobourg (Target V/5B)" [ = "Y" station Y7 "Anton"], 9 pp. Recce sorties in October of 1941, March & September of 1941, February, April, and September of 1942.
• Ref. 252L: "Sortosville-en-Baumont (Target V/6)" [ = "Knickebein" station K-10], 6 pp. Recce sortie in April of 1942.
• Ref. 252M: "Mt. Pincon (Target V/7)" [ = "Knickebein" station K-8], 4 pp. Recce sortie in June of 1941.
• Ref. 252N: "Greny (Target V/8)" [ = "Knickebein" station K-7], 5 pp. Recce sorties in June & October of 1941.
• Ref. 252P: "Mt. Violette (Target V/9)" [ = "Knickebein" station K-6], 5 pp. Recce sorties in June of 1941.
• Ref. 252Q: "Mt. de la Louve (Target V/10)" [ = "X" station X-#], 8 pp. Recce sorties in May & November of 1941, August & October of 1942
• Ref. 252R: "Cassel/La Croix Rouge (Target V/12)" [ = "Y" station Y2 "Berta"], 7 pp. Recce sorties in February of 1941, April & July of 1942.
• Ref. 252S: "Bergen op Zoom (Target V/13)" [ = "Knickebein" station K-5], 5 pp. Recce sorties in September & October of 1941.
• Ref. 252T: "Julianadorp (Target V/14)" [ = "Knickebein" station K-3], 4 pp. Recce sortie in March of 1941.
• Ref. 252U: "Bayeux/Le Mesnil (Target V/15)" [ = "Elektra" station 3], 4 pp. Recce sorties in April & June of 1942.
• Ref. 252V: "St. Valery-en Caux/St. Martin-aux-Bunaux  (Target V/16)" [ = "Y" station Y4 "Dora"], 5 pp. Recce sorties in June of 1942.
• Ref. 252W: "St. Valery-en Caux/Conteville de Palleul (Target V/17)" [ = "Y" station Y3 "Cicero"], 5 pp. Recce sorties in October 1940, May & July of 1942.
• Ref. 252X: "Boulogne/Boursin (Target V/19)" [ = "Y" station Y6 "Gustav"], 4 pp. Recce sorties in April & July of 1942.
• Ref. 252Y: "Petten/Groet (Target V/20)" [ = "Elektra" station E-#]   Sonne-5, between Petten and Groet (just north of Groet), Dutch coast., 4 pp. Recce sorties in July of 1941, June of 1942.
• Ref. 252Z: "Baumont / Hauge Town (Target V/21)", Y-type beam station, per Fig. in the Introduction.
• Ref. 252AA: "St.-Pierre-Église / Dargougerie (Target V/22)" [ = "Erika" station Er-2], 4 pp. Recce sorties in June of 1940, and April  of 1942.
• Ref. 252AB: "Morlaix/Plougourvest (Target V/25)" [= "Elektra" station 4], 3 pp. Recce sortie in September of 1942.
• Ref. 254: "Richtfunkfeuer und Drehfunkfeuer" [directional and rotating radio beacons], E. Kramar, Berlin, 18 pp., in "Ringbuch der Luftfahrttechnik", Vol. 15, VC3 (V. Ausrüstung, C. Funkpeilung, 3), Berlin-Adlershof, Zentrale f. wiss. Berichtswesen b. d. Deutschen Versuchsanst. f. Luftfahrt, 1938. [file size: 28 MB]
• Ref. 259: pp. 75-84 in "Zwischen Möhrenfeld und Panzerkute - verblassende Erinnerungen im märkischen Sand. Die märkischen Dörfer Groß- und Kleinbeuthen und ihre Umgebung in schwerer Zeit um 1945", Bernd Saalfeld, self published book (available via Heimatverein Beuthen e.V.), 2018, 156 pp.
• Ref. 261: German and Allied radar systems used in WW2 European war theatre
• Ref. 261A: "Hülsmeyer and the early days of radar inventions, sense and nonsense, a survey" and "Part II", Arthur O. Bauer, 2004/2005, 74 pp. (Part I) and 18 pp. (Part II). Source: www.cdvandt.org. [pdf Part I] [pdf Part II]
• Ref. 261B: radar-related articles from "IEEE Aerospace and Electronic Systems Magazine" and "Proceedings of the IEEE"
• Ref. 261B1: "IEEE HISTORIC MILESTONE - Christian Hülsmeyer: Invention and First Demonstration of Radar, 1904", Hugh Griffiths, Peter Knott, Wolfgang Koch, in "IEEE AES Magazine", Vol. 34, Issue 9 , September 2019, pp. 56-60. A preliminary version of this article is here, 9 pp. Retrieved 22 January 2020.  [pdf]
• Ref. 261B2: "The long prelude (1873-1922): Phase I of the invention of radar", J.B. McKinney, in "IEEE Aerospace and Electronic Systems Magazine", Vol. AES-21, Iss. 8, September 2006, pp. 17-25. Source: en.booksc.org, accessed April 2021. [pdf, See note 1].
• Ref. 261B3: "The rise of radio (1922-1930): Phase II of the invention of radar", J.B. McKinney, in "IEEE Aerospace and Electronic Systems Magazine", Vol. AES-21, Iss. 8, September 2006, pp. 27-39. Source: en.booksc.org, accessed April 2021. [pdf, See note 1].
• Ref. 261B4: "The arrival of radar (1930-1935): Phase III of the invention of radar", J.B. McKinney, in "IEEE Aerospace and Electronic Systems Magazine", Vol. AES-21, Iss. 8, September 2006, pp. 41-54. Source: en.booksc.org, accessed April 2021. [pdf, See note 1].
• Ref. 261B5: "The race with destiny (1935-1939): Phase IV of the invention of radar", J.B. McKinney, in "IEEE Aerospace and Electronic Systems Magazine", Vol. AES-21, Iss. 8, September 2006, pp. 55-73. Source: en.booksc.org, accessed April 2021. [pdf, See note 1].
• Ref. 261B6: "Radar becomes operational (1939-1941): Phase V of the invention of radar", in "IEEE Aerospace and Electronic Systems Magazine", Vol. AES-21, Iss. 8, September 2006, pp. 75-78. Source: en.booksc.org, accessed April 2021. [pdf, See note 1].
• Ref. 261B7: "GCA radars: Their history and state of development", H.R. Ward, C.A. Fowler, H.I. Lipson, in "Proceedings of the IEEE, Vol. 62, Issue 6, June 1974, pp. 705-716. Source: en.booksc.org, accessed 24 May 2021. [pdf, See note 1].
• Ref. 261C: "Some Aspects of German Airborne Radar Technology, 1942 to 1945", Arthur O. Bauer, 2 December 2006, 32 pp. Source: www.cdvandt.org, retrieved May 2019.
• Ref. 261D: "CH - The First operational Radar" [Chain-Home], pp. 73-83 in "GEC Journal of Research - Incorporating the Marconi Review", Vol. 3, No. 2, 1985. Retrieved 27 January 2020. [pdf]
• Ref. 261E: "Bomber's Radar - General Survey of the Three Primary Systems Used by Bomber Command", C.B. Baily-Watson, pp. 252-254 in "Flight", 6 September 1945.
• Ref. 261F: "Einsatz "Berlin"-Gerät" [Operation of "Berlin"-device = German version of the British "H2S" ground-mapping radar].
• Letter from Gen.Nafü (1.Abt.), addressed to gen.Nafü/Ln.Insp. (6.Abt.). Letter ref. Nr. 12493/44 geh. (1.Abt.II). Letter is dated 17 Juli 1944. Letter states that after referral with Generals Martini & Peltz, the IX.Fl.Korps will, until further notice, not use the "Berlin"-Gerät", as 1) current test/evaluation status is not yet sufficient for operational service, and 2) this navigation aid is not needed in the "Landekopfraum" [Allied landing/invasion area = Normandy]. The "Berlin"-Gerät" is not allowed to be used without permission from Lw.Fü.Stab.
• Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL 2-V/5, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 261G: Untitled letter/telegram about "Lichtenstein SN 2" and "Lichtenstein B/C"
• Letter/telegram from OKL Fü.Stab/Gen.Nafü.(Robinson), addressed to Luftfl.Kdo.1,4, 6. and Lw.Kdo. Südost. Letter ref. Nr. 10910/44. Letter is from 1944 (exact date not marked). Letter states that loss [to the enemy] of night fighter radar search equipment "Lichtenstein SN 2" must absolutely be avoided, to make it harder for the enemy to develop interference means. Therefore, night fighters missions with "Lichtenstein SN 2" over enemy territory and bandit territory [ = occupied territories with active resistance groups] is forbidden. Night fighters with missions over bandit territory in the East will only be equipped with "Lichtenstein B/C" until further notice.
• Source: BArch file nr. (Signatur) RL 2-V/5, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 261H: "Deflating British radar myths of World War II", Maj. G.C. Clark, Air Command and Staff College Research Dept., AU/ACSC/0609F/97-3.
• Ref. 261J: books about radar history and technology
• Ref. 261J1: "Radar Origins Worldwide: History of Its Evolution in 13 Nations Through World War II", R.C. Watson, Trafford Publishing, 2009, 420 pp.
• Ref. 261J2 "Die deutschen Funkmeßverfahren bis 1945" ["German radar through 1945"], Fritz Trenkle, Motorbuch Verlag Stuttgart, 1979, 209 pp.
• Ref. 261J3: "Radar Handbook", Merril I. Skolnik (ed. in chief), McGraw-Hill, 2^nd ed., 1990, 846 pp. Source: University of Zürich, Dept. of Geography, accessed 14 July 2020 [file size: 41 MB]. [pdf]
• Ref. 261J4: "Die Radarschlacht, 1939-1945: Die Geschichte des Hochfrequenzkrieges" ["The radar battle, 1939-45 - The history of the HF war"], Werner Niehaus, Motorbuch Verlag (publ.), January 1977, 246 pp.
• Ref. 261J5: "Technical History of the Beginnings of Radar" [basic principles of radar and historical aspects of their evolution; limited to the pre-cavity magnetron era of radar], Sean S. Swords, IET History of Technology Series 6, 342 pp. Source: b-ok.cc, retrieved 22 October 2020 [file size: 22 MB]. [pdf - See note 1].
• Ref. 261J6: "A Radar History of World War II: Technical and Military Imperatives", Taylor & Francis (publ.), 1999, 580 pp.; also: Institute of Physics Publishing, 1999, 563 pp.
• Ref. 261K: documents about the "Würzburg" radar (FuMG39/FuSE62)
• Ref. 261K1: "Geschichte der Funkortung - Funktionsmodell des Funkmessgerätes "Würzburg" FuMG 62 (D)" [History of radar, funtional model of the "Würzburg" radar], Hans-Peter Opitz, pp. 12-16 in "Funkgeschichte - Mitteilungen der Gesellschaft der Freunde der Geschichte des Funkwesens (GFGF)", Vol. 34, Nr. 195, February/March 2011. See note 1
• Ref. 261K2: "Funk-Sende-Empfangsgerät FuSE 62 (Flak-Meßgerät FMG 39 T)", Werkstattbuch part E 01-1, 7 pp. Source: www.cdvandt.org. Retrieved 2 September 2019. [pdf]
• Ref. 261K3: "Das Orten mit Fu.M.G. 39 T bei Feindstörung" [target location with FuMG 39T radar during enemy jamming & chaff/window/reflectors], Merkblatt, 1^st Flakdivision, 6 January 1944, 33 pp.Source: German Russian Project for digitization of archives in the Russian Federation. Retrieved 29 August 2019.
• Ref. 261K4: "Deckname „Würzburg“", Arthur O. Bauer, Verlag Historischer Technikerliteratur (publ.), 1966, 133 pp. Source: www.cdvandt.org. Retrieved 2 September 2019. [pdf]
• Ref. 261K5: "Geschichte der Funkortung - Funktionsmodell des Funkmessgerätes „Würzburg‟ FuMG 62 (D)", Hans-Peter Opitz, pp. 12-16 in "Funkgeschichte - Mitteilungen der Gesellschatf der Freunde der Geschichte des Funkwesens", Vol. 34, Vol. 195, February/March 2011.  See note 1
• Ref. 261L: p. 9 in "The Century of Radar - from Christian Hülsemeyer to Shuttle Radar Topography Mission", Wolfgang Holpp, based on his presentation "The Century of Radar" at the German Radar Symposium, Bonn/Germany, 2002 with 2004 update, 27 pp. [pdf]
• German version: "Das Jahrhundert des Radars - von Christian Hülsemeyer zur Shuttle Radar Topography Mission"  [pdf].
• Ref. 261M: "Deckname „Würzburg“ - Ein Beitrag zur Erhellung der Geschichte des geheimnisumwitterten deutschen Radargeräts 1937-1945" ["The technical history of the Würzburg radar system"], Arthur O. Bauer, Verlag Historischer Technikliteratur (publ.), 103 pp. Source: www.cdvandt.org. Accessed 28 March 2020. [pdf]
• Ref. 261N: "The History of Radar Technology in Germany - Reference to its Application to Radio Location" [Würzburg-A/C/Riese, Freya, Philips, GEMA, Lorenz 39L/40L, Elefant, Mammut, Seeburg, Lichtenstein SN2] , H. Diehl. Special Felkin report.
• Ref. 261P: "The State of German Centimetre Wave Technology at the End of the Second War", L. Brandt, special Felkin report?
• Ref. 261Q: "Eureka-H Radar Beacons in World War II" [VHF DME], F.R. Hunt, 12 pp., Chapter 14 of "Canadians on Radar - Royal Canadian Air Force 1940-1945", George K. Grande, Sheila M. Linden, Horace R. Macaulay, 2003; retrieved 2 May 2020.
• Ref. 261R: "Radar development in Canada" [WW2], Frederick H. Sanders, in "Proceedings of the Institute of Radio Engineers (I.R.E.)", Vol. 35, Nr. 2, February 1947, pp. 195-200. Source: worldradiohistory.com, retrieved 28 June 2020.
• Ref. 261S: "Microwaves detect aircraft" [Telefunken bi-static radar system, 10 cm wavelength / 3 GHz], in "Electronics, Vol. 10, nr. 9, September 1935, pp. 284-285. Source: worldradiohistory.com, retrieved 16 April 2021.
• Ref. 261T: "Air Navigation Systems: Chapter 5. The Development of British Airborne Primary Radar, 1935–1945", Brian Kendal, in "The Journal of Navigation", Vol. 47, Issue 3, September 1994, pp. 277-294. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 261U: articles about Doppler radar
• Ref. 261U1: "History of Doppler Radar Navigation", Walter R. Fried, in "Navigation: Journal of the Institute of Navigation", Vol. 40, Issue 2, Summer 1993, pp. 121-136. [Abstract] . Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 261U2: "A Historical Survey of the Application of the Doppler Principle for Radio Navigation", Ernst Kramar, in "IEEE Trans. on Aerospace and Electronic Systems", Vol. AES-8, Iss. 3, May 1972, pp. 258-263
• Ref. 261V: "The radar war, 1930-1945", Gerhard Hepcke (mediocre translation into English by H. Liebmann), 53 pp. Source: radarworld.org, accessed 5 September 2020. [brief overview/timeline keywords description of: pip-squeak, ILS, hyperbolic, Ingolstadt, Elektra, Sonne, Seetakt ship radar, Freya ground radar, Stichling IFF for Freya, Würzburg ground radar, Erstling IFF for Würzburg, Chain Home (CH) coastal ground radar, Type 79Y ship radar, Anti Surface Vessels (AVS) airborne radar, Air Intercept (AI) radar, Breslau I & II jamming stations, R3000 IFF, Masking Beacons (Meacon), Knickebein, X Procedure, Y Procedure, Postkutsche Procedure, Caruso jamming station, FuMB 1 Gee, Rebecca-Eureka, Heinrich, Metox R600 warning receiver, Olga warning receiver, Lichtenstein night fighter airborne radar, Mannheim FLAK radar, Moonshine, Wasserman groundradar, Karl jamming station, Wespe IFF, Leigh-light procedure, Oboe I Bumerang procedure, Window Chaff Tinsel, Würzlaus, K-Laus, H2S Rotterdam Gerät, Naxos & Naxos-W & Naxburg & Korfu airborne warnign receivers, Roderick jamming transmitter, Tuba ground jamming transmitter, SS Loran, Shoran, Hohentwiel U submarine radar, Oboe navigation procedure, Mandrel, Taxanble, Glimmer, Titanik, GH Discus, Feuerstein, Rotterheim, Berlin A & N1 & N2 airborne radar, Roland & Feuerball, Jagdschloß & Forsthaus ground panorama radar, Pauke gun laying radar] [pdf]
• Ref. 261W: radar articles from Wireless World magazine, source: worldradiohistory.com, retrieved Sept-2020 - Jan-2021
• Ref. 261W1: "Radiolocation - Part 1", R.L. Smith-Rose, in "Wirelesss World", Vol. LI, Nr. 2, February 1945, pp. 34-37, source: worldradiohistory.com, accessed 17 September 2020.
• Ref. 261W2: "Radiolocation - Part 2: History of its development", R.L. Smith-Rose, in "Wirelesss World", Vol. LI, Nr. 3, March 1945, pp. 66-70. Part 1 & 2 were reprinted as "Radar" [RDF, radiolocation, radar], R.L. Smith-Rose, in "Electrical Communication - A Journal of Progress in the Telephone, Telegraph and Radio Art", published by "International Standard Electric Corp.", Vol. 22, No. 3, 1945, pp. 171-178.
• Ref. 261W3: "Achievements of Radar - Its part in the war", in "Wireless World", Vol. 51, No. 9, September 1945, pp. 269-270.
• Ref. 261W4: "Fundamentals of Radar 1. - Ground stations: The development of Pulse Technique" [Chain Home (CH, CHL)], in "Wireless World", Vol. 51, No. 10, October 1945, pp. 299-303.
• Ref. 261W5: "Fundamentals of Radar 2. - Night fighter equipment : relation between power, beam width and range", in "Wireless World", Vol. 51, No. 11, November 1945, pp. 326-329.
• Ref. 261W6: "Fundamentals of Radar 3. - Radar as a weapon of offense : ASV and H2S", in "Wireless World", Vol. 51, No. 12, December 1945, pp. 363-365.
• Ref. 261W7: "Fundamentals of Radar 4. - Pulse methods applied to navigation" [Oboe, Gee], in "Wireless World", Vol. 52, No. 1, January 1946, pp. 23-26.
• Ref. 261W8: "Fundamentals of Radar 5. - Beacons employing pulse technique" [ASV, IFF, H2S, Eureka, BABS], in "Wireless World", Vol. 52, No. 2, February 1946, pp. 55-56.
• Ref. 261X: "A Brief History of the Development of Radar in Great Britain up to 1945", Richard M. Trim, in "Measurement and Control", Vol. 35, December 2002, pp. 299-301. Source: journals.sagepub.com, accessed 18 September 2020
• Ref. 261Y: "Radar for Blind Bombing - Part I & II" [H2X airborne radar], J.V. Holdam, S. McGrath, A.D. Cole, in "Electronics", Vol. 16, Nr. 5, May 1946, pp. 138-143, Vol. 16, Nr. 6, June 1946, pp. 142-149. Source: worldradiohistory.com, retrieved 25 October 2020.
• Ref. 261Z: "Directory of German Radar Equipment" [airborne and ground-based], War Department Technical Manual TM E11-219, Apri l1945, 74 pp.
• Ref. 261AA: articles about Oboe
• Ref. 261AA1: ""Oboe": How it Works", Air Ministry record AIR 20/1471, July 1943. Available at The National Archives (TNA), Kew/UK; catalog item description - I do not have a copy of this item. Please contact me if you do. Note: the TNA catalog includes 95 "AIR OBOE" records.
• Ref. 261AA2: ""Oboe": history compiled by No. 60 Group HQ", Air Ministry record AIR 16/917, 1940-1945. Available at The National Archives (TNA), Kew/UK; catalog item description - I do not have a copy of this item. Please contact me if you do. Note: the TNA catalog includes 95 "AIR OBOE" records.
• Ref. 261AA3: "Oboe: bomber navigation radar", Ministry of Aviation record AVIA 7/377, 1943-1944. Available at The National Archives (TNA), Kew/UK; catalog item description - I do not have a copy of this item. Please contact me if you do. Note: the TNA catalog includes 98 "AVIA OBOE" records.
• Ref. 261AA4: "Bumerangstörung im Ruhrgebiet" [Jamming of "Bumerang" (German codename for Oboe-guided British Mosquitoes) in the Ruhr area), Nr. 82 514/44 g.Kdos. (3.Abt.III). Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL 2-V/6, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016"
• Ref. 262: articles about hyperbolic radio navigation systems
• Ref. 262A: "GEE and LORAN - Radar Navigational Systems World War II", W.P. Campbell, 16 pp., Chapter 16 of "Canadians on Radar - Royal Canadian Air Force 1940-1945", George K. Grande, Sheila M. Linden, Horace R. Macaulay, 2003; retrieved 2 May 2020.
• Ref. 262B: "An Introduction to Loran", John Alvin Pierce, in "Proc. of the Institute of Radio Engineers (IRE) and Waves and Electronics", Vol. 34, Nr. 5, May 1946, pp. 216-234 . Source: worldradiohistory.com, retrieved 27 June 2020.
• Also reprinted as "An Introduction to Loran", John Alvin Pierce, in "IEEE Aerospace and Electronic Systems Magazine", Vol. 5, No. 10, October 1990, pp. 16-33. [pdf]
• Ref. 262C: "Robert J. Dippy: The Hyperbolic Radio Navigation System", Robert I. Colin, in "IEEE Trans. on Aerospace and Electronic Systems", July 1966, pp. 476-481.
• Ref. 262D: "GEE and LORAN - Radar Navigational Systems World War II", W.P. Campbell, 16 pp. [pdf]
• Ref. 262E: "1969 IEEE Pioneer Award - William Joseph O'Brien & Harvey Fischer Schwarz" [Award for invention, development, implementation of DECCA], in "IEEE Trans. on Aerospace & Electronic Systems", November 1969, pp. 1013-1020. [pdf]
• Ref. 262F: "LORAN Long Range Navigation", J.A. Pierce, A.A. McKenzie, R.H. Woodward, Vol. 4 of Massachusetts Institute of Technology (MIT) Radiation Laboratory Series, McGraw-Hill Book Co. Inc. (publ.), 1948, 490 pp. [file size: 25 MB].
• Ref. 262G: "LORAN (Long Range Aid to Navigation)", U.S. Dept. of Commerce, Civil Aviation Authorities (CAA), Airways Operations Training Series, Bulletin No. 7, June 1949, 16 pp., source: hathitrust.org, retrieved 6 June 2020.
• Ref. 262H: "The Loran system - Part I, Part II (Loran Receiver-Indicator), Part III (Loran transmitting-station)", in "Electronics", Vol. 15, Nr. 11, November 1945, pp. 94-99, Vol. 15, Nr. 12, December 1945, pp. 110-115, Vol. 16, Nr. 3, March 1946, pp. 109-115.
• Ref. 262J: "Decca Navigator - Continuous-wave navigation system", in "Wireless World", Vol. 52, No. 3, March 1946, pp. 93-95. Source: worldradiohistory.com, accessed 17 September 2020.
• Ref. 262K: "Decca Navigator stations - details of the transmitter chain", M.G. Scroggie, in "Wireless World", Vol. 52, No. 8, August 1946, pp. 260-262. Source: worldradiohistory.com, accessed 17 September 2020.
• Ref. 262L: "Air Navigation Systems Chapter 4. Hyperbolic Airborne Radio Navigation Aids – A Navigator's View of their History and Development", W.F. Blanchard, in "The Journal of Navigation", Vol. 44, Issue 3, September 1991, pp. 285-315. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 262M: "Early history of the Decca Navigator system", Claud Powell, in "Journal of the Institution of Electronic and Radio Engineers", Vol. 55, Issue 6, June 1985, pp. 203-209. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]]
• Ref. 262N: "The Genesis of the Decca Navigator System", Walter Blanchard, in "Journal of the Institution of Electronic and Radio Engineers", Vol. 68, Issue 2, March 2015, pp. 219-237. Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Ref. 262P: "Hyperbolic origins", Claud Powell, in "The Journal of Navigation", Vol. 34, nr. 3, September 1981, pp. 424-436.Source: en.booksc.org, accessed April 2021. [pdf, See note 1]
• Also see ref. 2C6.
• Ref. 263: articles about the C. Lorenz A.G. company
• Ref. 263A: "Das Auge am Marktgeschehen – Die Lorenz-Röhre und der Sieg nach 1945" ["Watching the market - the Lorenz valve and victory after 1945"], Jakob Tschandl, pp. 45-53 in "Fliegen und Funktechnik - Die Flugzeugfabrik der Luftwaffe Berline-Tempelhof 1933-1945" ["Aviation and radio - The Luftwaffe aircraft factory at Berlin-Tempelhof 1933-1945"], Marcus Popplow (ed.), Beate Winzer (ed.), Universitätsverlag der TU Berlin (publ.), 60 pp. Creative Commons License CC BY 4.0. Retrieved 22 May 2020.
• Ref. 263B: "Telephone and telegraph industry: Manufacture of equipment", pp. 42-50 in "American Industry in Europe", Frank Allan Southard, Vol. 6 of "The Evolution of International Business 1800-1945", Houghton Mifflin (publ.) 1931, 264 pp. Source: hathitrust.org. Accessed 22 May 2020.
• Ref. 263C: "ITT: The Management of Opportunity", Robert Sobel, Beard Books (publ.), 2000, 421 pp.
• Ref. 263C1: pp. 72-73 [Lorenz]
• Ref. 263C2: pp. 102-111, 158-161 [ITT, Federal Telephone & Radio Corp., Federal Labs]
• Ref. 263D: "75 Jahre Lorenz, 1880 - 1955. Festschrift der C. Lorenz Aktiengesellschaft Stuttgart" [keywords: Fernschreiber, "Goliath" transmitter, FuG 10, FuG 16, "Schwabenland" receiver, Funkhorchempfänger, Flugzeug Bordfunk, Richtfunk, Röhren, Funkortung], 1955, 272 pp. [file size: 53 MB; with OCR]. Source: archive.org.
• Ref. 263D1: "Lorenz-Beiträge zur Funkortung" ["Lorenz contributions to radio navigation"; Scheller beam, localizer, glideslope keyed equisignal, Elektra, SBA, , Australia], Ernst Kramar, pp. 155-162.
• Ref. 263D2: "Meilensteine der Großsendertechnik" ["Milestones of large transmitter technology"; "Goliath", Doherty Weißkirchen, Feldberg], Erich Schulze-Herringen, Erich Heineke, Felix Gerth, pp. 68-80.   [file size: 25 MB].
• Ref. 263E: "100 Years of Wireless Telephony in Germany: Experimental Radio Transmission from Eberswalde and Königs Wusterhausen", Wolfgang Mathis, Anja Titze, in "Advances in Radio Science" (ARS, an open-access journal of the Union Radio-Scientifique Internationale / International Union of Radio Science (U.R.S.I.) Landesausschuss Deutschland e.V., distributed under CCA 4.0 license), Vol. 19, pp. 93-104, Dec 2021.
• Also see ref. 164C.
• Ref. 265: articles about IFF, interrogator-transponder/responder, Distance Measuring Equipment (DME)
• Ref. 265A: "The Eureka-Rebecca compromises: another look at Special Operations security during World War II", Chris Burton, in "Air Power History", Vol. 52, No. 4, Winter 2005, pp. 24-37. Source: afhistory.org, retrieved 19 June 2020.
• Ref. 266: articles about radio course guidance via radiating & magnetic leader cables (C. Stevenson (1893), Owens (1901-1903), F.A. Kolster (1918/19), W.A. Loth, Blancard, E.J. Simon, A.H. Marriott, et al.)
• Ref. 266A: articles about the Loth system
• Ref. 266A1: "Le pilotage par câble électrique, système Loth, des navires et des aéronefs" ["Pilotage of ships and aircraft by means of the "Loth System" electric cable"], P. Letheule, in "Le Génie Civil : revue générale des industries françaises et étrangères", Vol. LXXIX, no. 24, no. 2052, 10 December 1921, pp. 505-510. Source: Bibliothèque nationale de France; public domain.
• Ref. 266A2: "The Loth guide cable - an interesting French aid to air navigation", in "Flight International Magazine", Vol. XIV, No. 11, 16 March 1922, pp. 163-164. Source: archive.org, retrieved 21 July 2020.
• Ref. 266A3: "The Loth guide cable for flying in fog. French invention for guiding aircraft through fog described. System functions in preliminary trial." in "Aviation" (predecessor of "Aviation Week"), Vol. 12, No. 15, 10 April 1922, pp. 422-423. Source: hathitrust.org, accessed 21 July 2020.
• Ref. 266A4: "The 'Loth leader cable system' for electrical steering of aeroplanes", John. S. Gray, in "Minutes of Proceedings of the Institution of Aeronautical Engineers", Nr. 9, 1923, pp. 7-30.
• Ref. 266A5: "Guidage magnétique des aéronefs et aérodromes de securité" ["The Magnetic Guidance of Aircraft; Safety Aerodromes"], William Loth, in "Comptes rendus hebdomadaires des séances de l'académie des sciences" ["Weekly minutes of the sessions of the academy of sciences"], Vol. 189 (July-December 1929), 14 October 1929, pp. 572-573. Source: Bibliothèque nationale de France; public domain. [Summary]
• Ref. 266A6: "The Loth navigation system: a twin rotating beacon method of emitting wireless signals that can be picked up on an ordinary receiver", R.J. de Marolles, in "Aircraft Engineering and Aerospace Technology", Vol. 2 No. 5, 1 May 1930, pp. 107-108. Source: en.booksc.org, retrieved 12 June 2021.
• Ref. 266A7: "Guidage Loth" ["Loth guidance"], pp. 349-351 in "Toute l'aviation", Edmond Blanc, 4^th ed., 1931, 494 pp. Source: Bibliothèque de France (BNF) on-line library, accessed 20 January 2022.
• Ref. 266D: NACA/NASA Reports & Memos. Source: NASA Technical Reports Server (NTRS).
• Ref. 266D1: "On the problem of guiding aircraft in a fog or by night when there is no visibility", William Loth, National Advisory Committee for Aeronautics (NACA), Technical Memo 57 (NACA-TM-57), January 1932, 5 pp. (translated from "Comptes redues des séances de l'académie des sciences", nr. 23, 5 December 1921). Source: NTRS, retrieved 21 July 2020. [Abstract]
• Ref. 266D2: "Automated landing, rollout, and turnoff using MLS and magnetic cable sensors", S. Pines, S.F. Schmidt, F.I. Mann, NASA Contractor Report 2907 (NASA-CR-2907), 1 October 1977, 152 pp. Source: NTRS, retrieved 21 July 2020.
• Ref. 266D4: "Results from tests, with van-mounted sensor, of magnetic leader cable for aircraft guidance during roll-out and turnoff" [B-737], James C. Young, W. Thomas Bundick, Stewart H. irwin, NASA Technical Paper 2092, January 1983. 40 pp. Source: NTRS, retrieved 24 August 2020.
• Ref. 266D4: "Results of aircraft open-loop tests of an experimental magnetic leader cable system for guidance during roll-out and turn-off", W. Thomas Bundick, David B. Middleton, NASA Technical Memorandum 4135 (NASA-TM-4135), NASA, Scientific & Technical Information Div., 1990, 39 pp. Source: NTRS, retrieved 21 July 2020.
• Ref. 266D5: "Effects of cable geometry and aircraft attitude of a magnetic leader cable system for aircraft guidance during rollout and turnoff", W. Thomas Bundick, NASA Technical Paper 1978, April 1982, 31 pp.
• Ref. 266D6: "Results of aircraft open-loop tests of an experimental magnetic leader cable system for guidance during roll-out and turn-off", W. Thomas Bundick, David B. Middleton, NASA Technical Memorandum 4135, NASA, Scientific & Technical Information Div., 1990, 39 pp. Source: NASA Technical Reports Server, retrieved 21 July 2020.
• Ref. 266E: newspaper articles
• Ref. 266E1: "Guiding aircraft in fogs - French to test new cable device" [Loth cable along top of telepgraph poles, planned 18 km section out of Le Bourget], in "The Manchester Guardian", 4 January 1923, p. 7.
• Ref. 266E2: "Air landing in fog" [buried Loth leader cable in circle around Le Bourget, left/above/right + relative strength for height; several years experimented at Farnborough], in "The Manchester Guardian", 1 August 1928, p. 8.
• Ref. 266E3: "Letters to the editor - The first wireless message" [Charles A. Stevenson claims invention of leader cable], in "The Observer", Vol. 147, No. 7677, 17 July 1938, p. 8.
• Ref. 266F: articles in "L'Aérotechnique", "L'Aérophile", "L'Aéro", and "Les Ailes" magazines - 1921-1935
• Ref. 266F1: "Utilisation des procédés Loth pour le guidage des avions par ondes hertziennes -  Partie 1: "Étude critique des procédés Loth pour la navigation aérienne" A. Verdurand, Partie 2 "Point de vue et réfutations de la S.I.P.L."" ["Use of the Loth method for guiding aircraft with radio waves - Part 1 "Critical review of the Loth method of air navigation", Part 2 "Opinion of, and rebuttal by, the Société Industrielle des Procédés Loth (SIPL) company"], A. Verdurand, J. Blancard, in "L'Aérotechnique", Vol. 8, Nr. 137, October 1930, pp. 363-376. Source: Bibliothèque nationale de France; public domain.
• Ref. 266F2: "Le guidage des avions par câbles électriques" ["Aircraft guidance by means of electric cables"], P. Franck, A. Volmerange, in "L'Aérotechnique", Vol. 4, nr. 33, February 1922, pp. 39-47. Source: Bibliothèque nationale de France; public domain.
• Ref. 266F3: "Le câble de guidage - son emploi pour atterissage sans visibilité" ["Guidance cables - their use for landing without visibility"], Paul Larivière, in "L'Aérotechnique", Vol. 17, Nr. 190, March 1935, pp. 33-39. Source: Bibliothèque nationale de France; public domain.
• Ref. 266F4: "La Navigation aérienne par temps de brume" ["Aerial navigation during fog"], A. de Gramont de Guiche, in "L'Aérophile", Vol. 29, Nr. 1-2, 1-15 February 1921, pp. 42-45. Source: Bibliothèque nationale de France; public domain.
• Ref. 266F5: "Les câbles-guides de M. Loth - La direction des aéronefs sans aucune visibilité" ["The guide cables of Mr Loth - aircraft guidance without any visibility"], P. James, in "L'Aérophile", Vol. 30, Nr. 1-2, 1-15 January 1922, pp. 18-21. Source: Bibliothèque nationale de France; public domain.
• Ref. 266F6: "L'infrastructure aérienne" ["Aviation infrastructure"], in "L'Aéro - Organe hebdomadaire de la locomotion aérienne", Vol. 25, No. 87, No. 1301, 5 May 1933, p. 5. Source: Bibliothèque nationale de France; public domain.
• Ref. 266F7: "La navigation dans le brouillard - où en est la pose du cable Loth" ["Navigation in the fog - the status on installation of the Loth cable"], in "Les Ailes - Journal hebdomadaire de la locomotion aérienne", Vol. 4, No. 180, 27 November 1924, pp. 2-3. Source: Bibliothèque nationale de France; public domain.
• Ref. 266G: "Finding aircraft landing stations by means of audio frequency receivers", Earl C. Hanson, in "Aerial Age Weekly", Vol. 9, No. 10, 19 May 1919, pp. 489-490. Source: hathitrust.org, retrieved 20 February 2021.
• Ref. 266H: "Underwater pilot cable", p. 335 in Chapter XXVIII in in "History of Communications-Electronics in the United States Navy", Linwood S. Howeth, Bureau of Ships and Office of Naval History, 1963, 698 pp. Source: hathitrust.org, retrieved 20 February 2021.
• Ref. 266J: "Making a technology fit: evolution of the leader cable system" [complete general history, 1893 - mid-1930s], pp. 46-56 in ref. 235J, .
• Ref. 266K: "Field localizers", p. 899 in ref. 229D5
• Ref. 266L: "Simon system" [concentric burried cables for approach to landing from any direction; unsuitable for airfield with runway(s)], pp. 35-36 in ref. 235P9.
• Ref. 266M: articles in "Nature" magazine, 1921
• Ref. 266M1: "The Leader Cable System", in "Nature", Vol. 106, No. 2767, 10 February 1921, pp. 760-762. Source: nature.com, accessed 20 August 2020. [pdf]
• Ref. 266M2: ""Leader" cables for aircraft", in "Nature", Vol. 108, No. 2721, 22 December 1921, pp. 539. Source: nature.com, accessed 20 August 2020. [pdf]
• Ref. 266P: "New fog-landing system installed at Materiel Division" [US Army Air Corps, "Loth" leader cable system (with U/I keying) for landing in fog, tested at Patterson Field, Dayton/OH/USA ], in "Air Corps News Letter", Vol. XVI, No. 1. 25 January 1932, pp. 8-9. Source: Air Force Historical Support Division, retrieved 6 September 2020.
• Ref. 266Q: "An Instrument Landing System", Edward Dingley, in "Communications" (merger of "Radio Engineering", "Communication & Broadcast Engineering", & "The Broadcast Engineer"), Vol. 18, Nr. 6, June 1938, pp. 7-9, 30-31. Source: worldradiohistory.com, retrieved 11 September 2020.
• Ref. 266R: "Piloting vessels by electrically energized cables" and "Discussion", A. Crossley in "Proc. of the Institute of Radio Engineers" (IRE), Vol. 9, Nr. 4, August 1921, pp. 273-299. Source: worldradiohistory.com, retrieved 19 February 2021.
• Ref. 266S: "Blind Landing Experimental Unit" [BLEU]. Source: wikiwand.com, retrieved 28 November 2020.
• Ref. 266T: "The Portsmouth "Leader" Cable", in "The Electrical Review", Vol. 86, No. 2209, 26 March 1920, p. 392 and No. 2211, 9 April 1920, p. 458.
• Ref. 266U: in ref. 235Y10 - pp. 9-16, 18 + Fig. 8-17 (leader cable at Ford Airport / Chicago-Lansing/IL/USA, Coock principle & patent, Loth system, Cromwell-Johannson Johansson ???? method)
• Ref. 266V: "Making a technology fit: evolution of the leader cable system", pp. 45-56 in ref. 235J1 ("Blind Landing", Erik M. Conway).
• Ref. 266W: "Leader cable guidance of an experimental field gantry" [agricultural], N.D. Tillett, T.G. Nybrant, in "Journal of Agricultural Engineering Research", Vol. 45, Issue: none, 1990, pp. 253-267. Source: en.booksc.org, accessed April 2022. [pdf, See note 1]
• Ref. 268: articles about acoustic (sonic) / electro-acoustic / capacitive / radio / radar altimeters
• Ref. 268A: pp. 26-42 [FuG101, FuG101A, AN/APN-1, FuG102, FuG103, SCR-718, AN/APS-13] in "Ein Beitrag zur Flugsicherungs Geschichte" ["A contribution about air traffic control history"], Hans H. Jucker, July 2014, 61 pp. Source: www.wrd.ch. Retrieved 18 May 2020.
• Ref. 268B: "Demonstration of clearance indicator for airplanes", pp. 84 in "Bell Laboratories Record", Vol. XVII, No. III, November 1948. Source: worldradiohistory.com, accessed 17 August 2020.
• Ref. 268C: "Historic firsts: radio altimeter", pp. 18-19 in "Bell Laboratories Record", Vol. 26, No. 1, January 1948. Source: worldradiohistory.com, accessed 17 August 2020.
• Ref. 268D: "Altitude by Radio", Cass H. Maxwell, in "Popular Aviation", Vol. XXVI, Nr. 2, February 1940, pp. 44-46, 94.
• Ref. 268E: "A Terrain Clearance Indicator", Lloyd Espenschied, R.C. Newhouse, in "The Bell System Technical Journal", Vol. XVIII, No. 1, January 1939, pp. 222-234. Source: worldradiohistory.com. Accessed 22 August 2020.
• Ref. 268F: "1967 Pioneer Award - Lloyd Espenschied, Russel Conwell Newhouse" [radio altimeter], Robert I. Colin, in "IEEE Transactions on Aerospace and Electronic Systems", July 1967, pp. 736-742. [pdf]
• Ref. 268G: "Funkhöhenmesser FuG 101a mit Frequenzmodulation" ["Radio altimeter FuG 1010 with frequency modulation"], Hans Jucker, 6 pp. Source: cdvandt.org, accessed 22 August 2020. Also see pp. 26-32 in ref. 268A.
• Ref. 268H: "Elektrischer Höhenmesser FuNG 101 - Kurzbeschreibung und Betriebsvorschrift E 93001" ["Electrical altimeter FuG 101 - description and operating instructions"], Luftfahrtgerätewerk Hakenfelde GmbH, 21 pp. Source: cdvandt.org, accessed 22 August 2020.
• Ref. 268J: "The sonic altimeter for aircraft" [history and status of the sonic altimeter], C.S. Draper, National Advisory Committee for Aeronautics, Technical Notes No. 611, August 1937, 127 pp. [file size: 74 MB; Abstract]. Source: NASA Technical Reports Server (NTRS), accessed 22 August 2020.
• Ref. 268K: "Pursuiters test sonic altimeter", in "Air Corps News Letter", Vol. XVI, No. 1. 25 January 1932, p. 14. Source: afhistory.af.mil, accessed 6 September 2020
• Ref. 268L: see ref. 235Y10 - pp. 16, 17 (acoustic, electro-acoustic, Behm System), p. 17 (radio), pp. 17-18 & Fig. 19 (capacitive)
• Ref. 280: Articles about bombing in general, incl. bomb aiming, bomb sights, and bomb trajectories
• Ref. 280A: Articles about the 1912 "Aéro-Cible Michelin", other 1912 bomb-aiming competitions, and bombing aspects, from the 1912 volume of "L’Aérophile - Revue technique & practique des locomotions aériennes - Bulletin officiel de l'aéro-club the France" ["Technical & practical review of aerial propulsion - Offcial bulletin of the Aero Club of France", 1893-1947]
• Ref. 280A1: "Prix de l’Aéro-Cible Michelin" ["The "Aéro-Cible Michelin" Prize"], in "L’Aérophile", Vol. 20, No. 3, 1 February 1912, p. 19. [First round will take place at Châlon, Feb 4 & 11, 1912. Target to have a 20 m radius (66 ft), marked by pickets spaced 2 m (6.5 ft) around the roped perimeter; 50 minutes per participant.]
• Ref. 280A2: "Autour du Concours de "L'Aéro-Cible Michelin"" ["About the Aéro-Cible Michelin competition"], Henri Mirguet, in "L’Aérophile", Vol. 20, No. 4, 15 February 1912, p. 76. [The result of the first round of the competition was “negative”: not a single hit of the target.]
• Ref. 280A3: "Une lance-bombes pour Aéroplanes et Dirigeables" ["A bomb-releaser for airplanes and dirigibles"], Robert Letelier, in "L’Aérophile", Vol. 20, No. 4, 15 February 1912, p. 87, 88. [Manual bomb release mechanism + photos thereof; trajectory diagrams per USN Lt. Riley E. (Estel) Scott]
• Ref. 280A4: "L'avion de guèrre" ["The war plane"], Henri Murguet, in "L’Aérophile", Vol. 20, No. 6, 15 March 1912, p.124. [Results of the first round of the Concours de “L’Aéro-Cible Michelin” were “not exactly brilliant”]
• Ref. 280A5: "L'Aéro-Cible Michelin", in "L’Aérophile", Vol. 20, No. 7, 1 April 1912, pp. 163. [Second round of the competition: supposed to take place on 24 March 1912 at Camp de Châlons, postponed to 21 April due to strong wind gusts. Three participants (2 military, 1 civil – with "Scott" bomb release device). Target (now) 20 m diameter. "Bomb" of 7.1 kg (15.7 lbs), 16 cm (6.3 inch) diameter.]
• Ref. 280A6: "L'Aéro-Cible Michelin", Robert Letelier, in "L'Aérophile", Vol. 20, No. 9, 1 May 1912, pp. 200, 201. [Report on first round of the series for the Prix de L’Aéro-Cible Michelin, 15 bombs each, 20 m diameter target, minimum altitude 200 m, photo of bomb hanging from airplane]
• Ref. 280A7: "L'Aéroplane, arme offensive – l’appareil de pointage" ["The airplane – offensive weapon – the aiming device"], Alex Dumas, in "L’Aérophile", Vol. 20, No. 10, 15 May 1912, pp. 223, 224. [The "Aéro-Cible Michelin" raised the issue of using the airplane as an offensive war machine. Bombers have to stay above the 500 m (1600 ft) height range of anti-aircraft artillery / gun fire. Increasing altitudes, so need to know more about bomb trajectory.]
• Ref. 280A8: "L'Aéro-Cible Michelin", in "L'Aérophile", Vol. 20, No. 12, 15 June 1912, p. 284. [Results of the competition on 26 May and 8-9 June, at Mourmelon [ = Camp de Châlons]. On 8 June, civilian Louis Gaubert with USN Lt. Scott as bomber, with his bomb release device, hit the target with 10 of 16 projectiles, but was disqualified for flying below 200 m).]
• Ref. 280A9: "Prix de 25.000 francs de l'Aéro-Cible Michelin - Prix de 50.000 francs de l'Aéro-Cible Michelin" [], Vol. 20, No. 15, 1 August 1912, p. 359. [Final rounds of the competition scheduled for 27-27 July and 10-11 August 1912 at Camp de Châlons. Prizes equivalent to appr. 80 and 160 thousand euros in Jan-2022. Source: france-inflation.com]
• Ref. 280A10: "L'Aéro-Cible Michelin", in "L'Aérophile", Vol. 20, No. 17, 1 September 1913, p. 400. [9 ,10, 15 August round of the competition: target 120x40 m (size of a dirigible airship hangar) and drops from 800 m (2600 ft) minimum altitude.]
• Ref. 280A11: "Résultats de l'Aéro-Cible Michelin 1912", in "L'Aérophile", Vol. 20, No. 18, 15 September 1912, p. 432. [Overall 1912 winner is civilian Louis Gaubert]
• Ref. 280A12: "Aéro-Cible Michelin 1912 : attribution des prix de 50.000 et 25.000 francs" ["Award of the 50 & 25 thousand francs prizes"], in "L’Aérophile", Vol. 20, No. 19, 1 October 1912, p. 454. [15 August. Winner (Louis Gaubert, civilian) hit the 20 m diameter target with 12 of 15 projectiles, from 200 m altitude.]
• Ref. 280A13: "L’Aviation en Allemagne - Concours de lancement de projectiles et d’applications militaires en aéroplane" ["German aviation - projectile dropping competition and military airplane applications"], in "L’Aérophile", Vol. 20, No. 19, 1 October 1912, p. 445, 446. [Military competition at Gotha/Germany, 17-19 August. Organized by the Deutscher Fliegerbund and the Reichsflugverein. Stationary ground target 100x100 m, 7.1 kg dummy bombs, minimum altitudes 200 m, 400 m (target size + 50%), and 600 m (target size + 100%); moving target (tethered balloon, 30 m long, 3 m diameter, 4 m above ground) from minimum 50 m altitude; intercepting a dirigible.]
• Ref. 280B: articles about bomb sights
• Ref. 280B1: "Deconstruction the myth of the Norden bombsight", Michael Tremblay, University of Victoria/BC/Canada, Master of Arts thesis, 2007, 150 pp. Source: library.uvic.ca, retrieved 30 June 2021.
• Ref. 280B2: "The bombsight", in "US Air Forces At War", special issue of "Flying", Vol. 33, No. 4, October 1943, pp. 103-107, 342-344.
• Ref. 280B3: "Notes on enemy bombsights" and "Notes on enemy bombsights (concluded)", F. Poslethwaite, in "Aircraft Engineering and Aerospace Technology", Vol. 14, Nr. 9, September 1942 [pdf] , pp. 244-247, 250 and Vol. 14, Nr. 10, October 1942, pp. 276-280 [pdf]. Source: en.booksc.org, &  en.booksc.org respectively. Retrieved 30 June 2021.
• Ref. 280B4: "Close-up of the Norden bombsight", Volta Torrey, in "Popular Science", Vol. 146, No. 6, June 1945, pp. 70-73, 220, 224, 228, 232.
• Ref. 280C: articles about bomb trajectories
• Ref. 280C1: "Der Bombenabwurf" ["The bomb drop"], Bachofener, in "Allgemeine schweizerische Militärzeitung = Journal militaire suisse = Gazetta militare svizzera", Vol. 82, Nr. 1, January 1936, pp. 296-304. Source: e-periodica.ch, retrieved 18 June 2021.
• Ref. 280C2: "Bomb trajectories", Edwin Bidwell Wilson, National Advisory Commission on Aeronautics (NACA), Technical Report No. 79 (NACA-TR-79; reprint from 5^th annual report), 1920, 9 pp. Source: ntrs.nasa.gov, retrieved 28 June 2021.
• Ref. 280C3: "Weapon Delivery Analysis and Ballistic Flight Testing", R.J. Arnold, J.B. Knight, Vol. 10 of "AGARD Flight Test Techniques Series", Advisory Group for Aeronautical Research and Development (AGARD), North Atlantic Treaty Organization (NATO), AGARDOgraph 300, Technical Report RDP, 1 July 1992, 172 pp. Source: www.sto.nato.int, retrieved 21 June 2021.
• Ref. 280C4: "Theory of horizontal bombing", pp. 233-234 in Section D of "Aircraft fire control", in Chapter 23 of "Fire Control", Vol. 2. of "Naval Ordnance and Gunnery", Dept. of Ordnance and Gunnery, United States Naval Academy, Bureau of Naval Personnel (ed.), NAVPERS 10798-A, 1958 revision of the 1950 edition, 508 pp. Source: eugeneleeslover.com,, retrieved 21 September 2021.
• Ref. 280D: articles about bombing & military aviation in general
• Ref. 280D1: "Clément Ader, inventeur d’avions" ["Clément Ader, inventor of airplanes"], Pierre Lissarague, Bibliothèque Historique Privat (publ.), 1990, 320 pp., ISBN-10: 2708953559.
• Ref. 280D2: pp. 264, 265, 280, 281, 438, 439 in "The Proceedings of the Hague Peace Conferences - Translation of the Official Texts - The Conference of 1899", Div. of International Law of the Carnegie Endowment for International Peace, Oxford University Press (publ.), 1920, 905 pp. English translation of the 1907 edition by Martinus Hijhoff (publ.) of the original proceedings of the 1899 Conference by the Foreign Office of The Netherlands: "Conférence internationale de la paix. La Haye, 18 mai - 29 juillet 1899. Ministère des affaires étrangères. La Haye, 1899". Source: US library of Congress, retrieved 2 January 2022.
• Ref. 280D3: "La militarisation de ciel" ["The militarization of the sky”], pp. 8.9-8.23 (pdf pp. 342-365) in "Août" ["August"], Chapter 8 in "L’année aéronautique 1912 à travers le quotidien Le Petit Parisien" [file size: 174 MB] ["The aeronautical year 1912 seen through the daily newspaper Le Petit Parisien"], Joel Vergne, Yves Meusburger (ed.), Collection Mémoire de l'Aviation Civile, Direction Générale de l'Aviation Civile (DGAC), 2013, 2015, 760 pp. Source: calameo.com, accessed 9 January 2022.
• Ref. 280D4: "Gli ufficiali aviatori iniziano la guerra nuova gettando bombe in un accampamento nemico" ["Airmen officers start the new war by dropping bombs at an enemy camp"], on the frontpage of "La Stampa" newspaper, Vol. XLV, Nr. 304, morning edition of Thursday 2 November 1911. Source: archiviolastampa.it, accessed 10 January 2022. A transcript and Google translation to English (with improvements/corrections by me) is here.
• Ref. 280D5: "Pour que nous ayons des aéroplanes" ["So that we shall have areoplanes"], open letter to the editor-in-chief by André Michelin, in "Le Matin" newspaper, Vol. 28, Nr. 10145, 7 December 1911, p. 1. Source: Bibliothèque de France (BNF) on-line library, accessed 13 January 2022.
• Ref. 280D6: p. 176 in "Aeroplanes and airships as national and collective symbols in Western Europe before the First World War (1908-1914)", Florian Schnürer, in "Memoria y Civilización", Vol 12, 2009, pp. 155-189. Source: Universidad de Navarra, accessed 12 January 2022
• Ref. 280D7: "Dirigibles in Tripoli War - Drop bombs among Turks", in "The New York Times", 7 March 1912, p. 4.
• Ref. 280D8: "Aeroplanes in Tripoli War", in "Flight - First Aero Weekly in the World", No. 191 (Vol. IV, No. 34), 24 August 1912, p. 784. Source: archive.org, accessed 17 January 2022.
• Ref. 280D9: "Foreign News - Tripoli", in "Aircraft", Vol. 3, No. 2, April 1912, p. 46. Source: archive.org [file size: 48 MB], accessed 17 January 2022.
• Ref. 280D10: p. 290, 291 in "Practical military aviation", J.H. Worden, in "Aircraft", Vol. 3, No. 10, December 1912, pp. 289-291. Source: archive.org [file size: 48 MB], accessed 17 January 2022.
• Ref. 280D11: "A history of aeronautics" [file size: 35 MB], Evelyn Charles Vivian, William Lockwood Marsh; Harcourt, Brace & Co. (publ.), 1921, 521 pp.
  Source: archive.org, retrieved 17 January 2022.
• Ref. 284: "Report on interrogation of C.S.O., Luftflotte Reich Schleswig (General Bohne) and those available of his technical staff", D.C. Nutting, Report No. R-169/RAF, Air Technical Intelligence (A.T.I.) Headquarters, 2^nd Tactical Air Force (T.A.F.) (M), 28 May 1945, Declassified IAW EO 13526, 15 pp. [Keywords: ground radar (Elefant, Jagdschloß, Forsthaus, Jagdhütte, Jagdhaus, Heidelberg, Tannenbaum, Freya Fahrstuhl, Naxos, Korfu, ground jamming (Anti-Bumerang/OBOE, Anti-Rotterdam/H2S), airborne radar (SN2, SN3), aids to automatic weapon-firing (Elfe, Grom, Pauke-Pauke, Berlin N, Bremen-O, FuG-244, FuG-245), homing devices (FuG-221, Naxos, SN3 Biene), IFF (Allied IFF, FuG-226 Neuling, Infra-Red IFF), airborne infra-red (Falter, Kiel), airborne radio (FuG-224), navigational aids (Komet, Hyperbel, Bernhard/Bernhardine, Hermine, Erika), German A.T.I. (organisation, crashed aircraft)]. Source: The National Archives of the UK, used in accordance with the Open Government License [pdf].
• Ref. 3, 285, etc: to be allocated.

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