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Latest page updates: April 2023 (added ref. 228V17 and associated text)

Previous updates: January 2023 (expanded description of the Orfordness beacon transmission sequence); June 2022 (made into separate page; added ref. 230R8, 245B-245D); 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).

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Directional radio beacons can be thought of as the radio equivalent of optical rotating beacons: nautical lighthouses. They assist  navigation at sea and on inland waterways, and also mark points of danger to shipping. In December of 1905, Lee de Forest patented his "Aerophore" concept of radio-based equivalent: a rotating-beam radio beacon. His US patent nr. 833034 proposes some form of directional antenna (e.g., parabolic reflector, or a slanted mono-pole antenna per ref. 186Q1) that is slowly rotated, and a spark gap transmitter. It is unclear if, or to to what extent, de Forest's beacon was ever built and tested. He also saw possibilities for traffic collision warning between ships equipped with the same system, and likewise between trains operating on the same track. Ref. 186Z (pp. 259, 260).

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

Note that the parabolic/cylindrical reflector was not new: it was invented by Heinrich Hertz during his late 1880s experiments, used in 1900 by Jonathan Zenneck (ref. 186G), by Lee de Forest in 1901, and in 1902 by Karl Ferdinand Braun. The latter also invented the Cathode Ray Tube (CRT, Braun's Tube, D: "Braun'sche Röhre"), the oscilloscope in 1897, the capacitor-inductor oscillator circuit in 1901, and a rotable directive transmitter in 1905. So, de Forest's contribution is limited to the code disk and application to radio location / navigation.


Fig. 1: Lee de Forest's December 1905 "Aerophare" concept of a rotating directional beacon with sector identification

(source: adapted from US patent 833034)


During first decades of the 20th century, there was a lot of experimentation going on in the field of directional antenna systems (ref. 185M), the use of directional radio reception and transmission, in particular for maritime navigation. Most of it contributed to knowledge and experience, but did not lead to long lived applications. The latest version of the Telefunken Compass was the first operational continuously rotating beam beacon. An interesting British example of a large rotating beam system is the one constructed in 1920 on the small isle of Inchkeith in the Firth of Forth, some 10 km northeast of downtown Edinburg/Scotland. Ref. 228V6. It was a cooperation of the Marconi company (designed and developed by Charles Samuel Franklin) and Trinity House, in its role as General Lighthouse Authority (which, by the way, had no authority in the Scottish part of Great Britain). It was based on Marconi's late 1890s and 1916 experiments in Italy with rotable parabolic cylindrical reflectors and 2-3 m wavelength (100-150 MHz), ref. 228V6, 228V14.

Heinrich Hertz was the very first to use this type of radio reflectors (1888, ref. 228V16). The Marconi beacon had two such reflectors, installed back-to-back, and with an aperture of 8 m. However, instead of a solid metal surface, these reflectors were "curtain" screens, each made up of about two dozen parallel vertical wires, spaced about 30 cm (1 ft). Also see the 1919 US Marconi/Franklin US "reflectors" patent nr. 1301473. A solid surface would have been much too heavy, expensive, and with a very high wind load. A spark transmitter with a wavelength of 4 m (75 MHz) was used.

The initial wooden-frame beacon at Inchkeith was operated for about a year, and tested with the steamship "S.S. Pharos" during the fall of 1920. A vertical monopole transmitter antenna was placed on the axis of symmetry of each parabola, at the focus of the parabola - about ¼ wavelength in front of the reflector. This configuration generated two sharp radio beams in opposite directions, sweeping at a constant speed of ½ rpm (one revolution in 2 minutes = one beam passage per minute!), very much like an optical lighthouse. Each reflector had its own transmitter. It operated on a wavelength around 4 m (ref. 228V2), i.e., a frequency around 70 MHz (VHF). Ship-board, only a simple receiver installation was required (ref. 228V8). However, due to the beacon's operating frequency, it had to be a special short-wave receiver, which was not standard equipment at that time. Ref. 228A. During the second half of 1921, the initial beacon was replaced with a larger one - with a steel structure. The antenna system was about 10 m tall (32 ft per ref. 228V3, 228V5), with arms of similar length (ref. 185F, p. 34). The 4-arm upper structure had a diameter of 13 m (43 ft). It was tested with the "S.S. Royal Scot", a ship of the London & Edinburgh Steamship Co. Ltd. Beam patterns were determined at wavelengths of 4.28 m, 5.54 m, and 6.14 m, i.e., at around 70, 54, and 49 MHz. The installation reached a satisfactory state by mid-1922, with a successful official demo in November of that year. Ref. 228V3.

Inchkeith beacon

Fig. 2: The  antenna of the Marconi Rotating Beam system - under construction on Inchkeith

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

Inchkeith beacon

Fig. 3: Receiving antennas for the Marconi Rotating Beam system on the "S.S. Royal Scot"

(source: adapted from ref. 228V1; 8 ft length of the dipole antenna corresponds to a wavelenght of ≈4.8 m :: ≈62 MHz)

To enable the receiving station to determine its bearing from the beacon, the beacon sent a distinct Morse signal at each of the 64 half-compass-points, i.e, every 5.625°. See see Fig. 4 below. I.e., the same approach as pioneered by Lee de Forest's 1905 concept and the 1909 stepwise rotating beam system of the Prussian Building Authority. The 360° dots-and-dashes sequence of the Marconi beacon was transmitted at an equivalent Morse Code Speed of 10 words per minute (WPM), so it could "be read comfortably by an intelligent person without special training". I.e., no wireless operator required (ref .228V3). Note that 10 WPM officially actually corresponds to about ≈ 50 characters/min, whereas 64 characters every 2 minutes is only ≈ 6 WPM... Even more comfortable! A bearing accuracy of a quarter compass point was obtained (≈2.8°). Ref. 228V2, 228V3.

Marconi beacon morse codes

Fig. 4: The "bearing corrector" tool with the Morse Code letters for the 64 half compass points on the compass card

(source: compass card adapted from ref. 228V3; illustration adapted from ref. 228V14)

As stated above, each reflector had its own transmitter system. They were identical. Each transmitter was a 2-stage spark transmitter system. The first stage was located near the rotating beacon. It was a 1/2 kW Marconi rotary-gap spark transmitter, driven by a constant-speed AC motor. The multi-contact rotary spark gap was adjusted such that the timing of its sparks coincided ( = were synchronized) with the peaks of the AC power cycle. I.e., it was a so-called synchronous spark transmitter. This technique maximizes the transmitter output power. See the "Transmitter technology: 1865-1940" section. This transmitter was keyed on/off in the rythm of the Morse characters. This keying was done with a heavy relay that interrupted the AC power to the transmitter. It was energized/deenergized by a switch, actuated by contact plates that were attached to the outside of the rotating base of the beacon (see Fig. 5 & 6). The output of this transmitter was passed to the second transmitter stage, located on the rotating base of the beacon, via a set of slip rings. , at the focus of the parabolic reflector. See both images in Fig. 2 above.

Marconi beacon Inchkeith transmitter

Fig. 5: The 2-stage spark transmitter system (one per reflector), installed on the rotating platform of the beacon

(source: adapted from Fig. 4 in ref. 228V3)

The second transmitter stage was housed in a metal case (contrary to what Fig. 5 suggests, the transmitter case was oriented vertically, see Fig. 2). It comprised a Tesla transformer to increase the amplitude of the high frequency power. This was passed to a "pressure circuit", see Fig. 5 & 7. This contraption was developed by C.S. Franklin: a closed metal cylinder containing a high-voltage capacitor of ≈ 111 picofarads ( = 100 statfarad = 100 cm), in series with a spark gap. The air pressure in the cylinder was increased to 500 psi (≈ 34.5 bar), which significantly increased the dielectric strength of that air in the cylinder, allowing a smaller spark gap. This reduced damping of the spark pulse-trains, resulting in a more constant amplitude of the generated high frequency signal. The output of the "pressure circuit" was connected to the vertical rod antenna via an adjustable coupling.

Marconi beacon Inchkeith drive gear

Fig. 6: The electric motor and worm gear, driving a pinion that engaged radial steel pins on the ring of the revolving platform

(source: adapted from Fig. 2 in ref. 228V3)

Marconi beacon Inchkeith pressure circuit pattern receiver

Fig. 7: The "pressure circuit", radio receiver of the "S.S. Royal Scot", and radiation pattern of the Inchkeith beacon beam

(source: Fig. 5, 8, and 6 in ref. 228V3)

Ca. 1923, Marconi erected a second revolving double-reflector beacon: next to the South Foreland Light Station (lighthouse), just to the northeast of Dover/England, right above the famous white cliffs. Ref. 228V11. Its 250 watt transmitter operated on a wavelength of about 6 m (≈50 MHz). This antenna system had a flat reflector plane instead of parabolic. The passive reflector rods were installed at 1/4 wavelength (≈ 1.5 m) behind the energized antenna rods. See Figure 8 below. Like the Inchkeith beacon, it rotated at 0.5 rpm. It had a range of 50-100 miles. Range and beam shape (ca. 15° aperture) were determined with a receiver on Marconi's private steam yacht - the "Elettra", which served as his seaborne laboratory for wireless experiments. Ref. 228V17.

Marconi South Foreland beacon

Fig. 8: South Foreland lighthouse with Marconi's revolving beam beacon (1925) and the antenna radiation pattern

(source: adapted from ref. 228V17)

Here too, the Morse code characters were transmitted at a speed of about 10 words per minute. Ref. 228V17.

Marconi South Foreland beacon

Fig. 9: Actuation of the transmitter on/off switch by notches on a ring below the antenna of the 1925 South Foreland bacon

(source: adapted from ref. 228V17)

Around 1928, Marconi abandoned his rotating beam developments, in favor of his commercial radio communication activities. The next photo shows the last antenna configuration:

Marconi South Foreland beacon

Fig. 10: South Foreland lighthouse with Marconi revolving beam beacon to the right - ca. 1930

(source: photo adapted from St. Margaret's Village History)


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

Orfordness Beacon


(source: based on ref. 228H4)

Early 1928, it was concluded that these experiments were promising enough to warrant full-scale trials with a more permanent beacon. The decision to proceed was taken shortly thereafter. The costs and the work were to be shared by the Air Ministry and Trinity House. Ref. 228K. In November of 1928, the cost was estimated at GB£5k, ref. 228J. Based simply on the inflation rate data for general goods and services, this would be equivalent to about £316 thousand in 2019 (≈€360k, ≈US$428k). The site selected for these trials was the Orford Ness, for its coastline location and for financial reasons. A "ness", from Middle and Old English for "nose", is a peninsula or cape. This narrow foreland is some 15 km (≈9 miles) long, and is separated from the Suffolk/England mainland by the Alde-Ore estuary. The widest part of the ness is off the village of Orford, about 130 km (≈80 miles) northeast of downtown London.


Figure 11: TITEL*****************

The ness was acquired by the British War Department in 1913/14. The ness became the site of the first Royal Flying Corps (RFC) air research station in 1913. The associated military airfield became operational in 1915.  XXXXXXXXXXXXXXXXXXXXXXXXXXXXX

The Ness became a military site in 1915, when the Royal Flying Corps established an experimental squadron there, for reasearch of weapons and navigation. It remained a restricted military site through 1982. Activities included WW2 radar development, conventional and atomic weapons research, and over-the-horizon (OTH) radar trials.

In 1935, British Air Ministry set up the Orfordness Research Station (ORS) for the development of Radio Direction Finding (RDF), for the purpose of detecting and tracking aircraft. RDF was the term used in Britain until the US acronym "radar" for "Radio Detection and Ranging" became current ca. 1943. The first British radar station was built at the ORS in 1935, as was the first Chain Home (CH) early-warning radar station in 1937. Note that, as finally recognized by the IEEE in 2019, the world's first radar was invented, patented, and publicly demonstated in Germany and The Netherlands in 1904 by Christian Hülsmeyer. See the radar page.

Anyway, in March of 1936, the Air Ministry acquired Bawdsey Manor, about 8 km (5 miles) southwest of the Oreford Ness, at the mouth of the river Deben. The ORS was moved there, and renamed Bawdsey Research Station (BRS). This was the central radar research group. In 1939, with the threat of war and attack becoming real, it moved north up the east coast, to the CH radar station near Dundee/Scotland. At the occasion, it was renamed Air Ministry Research Establishment (AMRE). May 1940 it was time to move and be renamed again: to Worth Matravers near Swanage/Dorset on the south coast - 100 km due north of Normandy/France. Now it operated under the Ministry of Aircraft Production, as Ministry of Aircraft Production Research Establishment (MAPRE). In November of that year, it was purposely given the misleading name Telecommunications Research Establishment (TRE). Inevitably, the activities there began to attract German attention. Around May of 1942, the organisation moved to Malvern in the West Midlands, about half way between Bristol and Birmingham. The War Office's research organisation Air Defence Research and Development Establishment (ADRDE, created in 1941), moved to Malvern at the same time. It too was involved with radar. It was renamed Radar Research and Development Establishment (RRDE) in 1944 and merged with the TRE in 1953. Combined, their name was Radar Research Establishment (RRE), renamed the Royal Radar Establishment in 1957. Renaming and reorganisations continued to modern times.

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

Orfordness Beacon

Fig. 12: The Orfordness Beacon with barracks to the left and electrical "power house" to the right

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

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

The loop antenna was a small multi-turn square "frame coil" loop with sides of 1.8 - 3 m (6-10 ft square, ref. 228M). The loop was vertically oriented and mounted on a vertical wooden shaft that poked through the roof of the beacon. No other technical details are available regarding this antenna.

The antenna rotated with a speed of 1 rpm, i.e., 6° per sec. To ensure accuracy of the system, this speed had to be constant and precise. This was achieved with a "phonic motor" (ref. 228K). Its concept was invented by Poul la Cour in Denmark in 1885, and patented by him in Britain in 1887. Ref. 228P. It was originally used to synchronize telegraphy and teleprinter systems, as well as J.L. Baird's television system. In essence, it uses a stable electric oscillator to drive a synchronous motor. Since the 1920s, this was implented with a simple electronic audio tone generator. Its signal drives an electromagnet that is coupled to a mechanical tuning fork and continuously excites the fork. Tuning forks can only oscillate at a specific audible frequency (hence "phonic"). The resulting precise, constant fork vibration is captured via capacitive coupling. This signal is then amplified to the required power level for the synchronous AC motor. The fork's frequency was based on the rpm set-point and the number of poles per phase of the AC motor. Deriving an audio frequency from a highly stable and precise source, such as a high frequency quarz crystal oscillator, was neither practicable, nor were such oscillators and the necessary frequency dividers available at the time. Per ref. 228L, this drive system maintained the beacon's 1 rpm to within 0.01 sec per rev. (note: this implies a rather impressive 0.02%!). "North" was aligned with True North, not Magnetic North (ref. 228N). In modern aviation, beacons such as VOR (VHF Omi-directional Range) are referenced to Magnetic North, not True North, because local Magnetic North is the only reference direction that can still be determined when all of the aircraft's electrical and vacuum systems have failed. I.e., when only the magnetic "whisky" compass remains ("whiskey" in the USA and Irleand).

Orfordness Beacon

Fig. 13: The Orfordness Beacon - with what the antenna might have looked like, and the loop radiation pattern

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

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

In April of 1930, it was decided to build a second such beacon, at the Royal Aircraft Establishment (RAE) site at Cove near Farnborough/Hampshire (ref. 228H4, 228K). The RAE had a Radio & Navigation Department at Cove. The stated objective was "to test the general utility of this system of direction finding and to ascertain in particular, whether by obtaining bearings from the two beacons [ = triangulation], aircraft can fix their position with sufficient accuracy for practical purposes". The beacon became operational in November of 1930. The Cove/Farnborough beacon transmitted during the five-minute intervals during which the Orfordness beacon was silent. The loop antenna at Franborough was a 5x5 ft (≈1.5x1.5 m) square, with six turns of wire. To reduce the loop's loss resistance (important, as the antenna was extremely small compared to the wavelength), the wire comprised 1458 insulated strands of SWG 40 wire ( = 0.1118 mm diam). It was used with a transmitter that dissipated 2.5 kW, producing an antenna feed current 72 amps. Radiated power was estimated at only 120 W. Ref. 228R, 228S1.

Orfordness Beacon

Fig. 14: Particulars of the two primary beacons XXXXXXXXXXXXXXXXXX REMOVE MAP PART  &ASSOCIATED REF

(source: based on ref. 228H4; rfe. 228R states 707 m for the wavelength of the Farnborough beacon)

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

Note that ref. 229A8 (p. 57; 1936) states that a complete transmission sequence took 5 minutes. During the first minute, the 3-letter station call sign was sent in slow Morse code, followed by a constant signal ( = long dash of about 12 sec). This took 30 sec, and was repeated once. This started at the East/West passage of the null of the rotating beam pattern. The remaining four minutes were used for transmitting the actual navigation signals. The North-signal was sent just before the North/South passage of the null of the rotating beam pattern. This marker was the Morse code character "V" followed by two dots. I.e., "• • • ─ • •". This was followed by a constant tone of about 12 sec, starting exactly at the time of that passage. "B + two dots" was used for the East marker. I.e., "─ • • • • •". This was followed by a constant tone of about 45 sec, starting exactly at the time of the latter passage. This 60 sec sequence was repeated three times.

A "sufficiently accurate" stopwatch or other chronograph had to be used. Such a stopwatch could have a special dial "somewhat similar in type to that proposed for use with the Telefunken Compass in 1912" (ref. 228L), see Fig. 15 below. Instead of a stopwatch, a sort of strip-chart or other ondulator recorder could also be used to measure the time between "North" or "East" signal and subsequent "null" passage. The recorder could be automated. Ref. 228M, 235P45.

Orfordness Beacon stopwatch

Fig. 15: Stopwatch dials for use with the rotating beacon

(source: adapted from ref. 228L)

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

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

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


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

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

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

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


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

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