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INTRODUCTION

The "Bernhard/Bernhardine" system is a radio-navigation system that was used by the Luftwaffe to assist fighter aircraft with the intercept of enemy bombers. The system went into operational service late 1941. Ref. 1, 2, 3, 4, 5, 6, 7A, 8, 85A/B/C, 164, 181, 183. As shown in Figure 1, the system comprises a beacon station and a Hellschreiber printer-system in the aircraft:

  • FuSAn 724/725 "Bernhard" is the VHF rotating directional-beacon ground-station (UKW-Richtstrahl-Drehfunkfeuer). It continuously transmits the station identifier and the momentary antenna azimuth (bearing) in Hellschreiber-format. Instead of the azimuth, some stations could broadcast short "Reportage" text messages, with instructions for intercepting inbound enemy bombers. Note that the system was only operating (thus rotating) when enemy aircraft were in range and fighter planes had to be directed towards them.
  • FuG 120 "Bernhardine" is the airborne Hellschreiber system that prints the data stream from the selected Bernhard station. Hence, it is a "UKW-Richtstrahl-Drehfunkfeuer-Empfangszusatz mit Kommandoübertragung". That is, an accessory for a (standard) VHF directional-beacon radio receiver, that also provides command uplink (if the ground-station is equipped for that).

As it operated in the 30-33.1 MHz frequency range, it is by definition a VHF system (30-300 MHz). However, from a radio propagation point of view it behaves more like an HF system (3-30 MHz).


Bernhard Bernhardine system diagram

Fig. 1: "Bernhard/Bernhardine"  = "Bernhard" ground-station + "Bernhardine" airborne Hellschreiber printer system

(click here for a full size image)

The "Bernhard" ground-station has a rotating antenna system that consists of two antenna sub-systems (both dipole arrays):

  • One dipole array has a single-beam radiation pattern (green in Figure 2 below). It is used to continuously transmit data in Hell-format (station identifier and momentary antenna azimuth, or a short "Reportage" text message). The centerline of the beam is the azimuth of the antenna.
  • The second (larger) antenna system (two dipole arrays) has a twin-beam radiation pattern (purple in Figure 2). The pattern has a sharp null between the two beams. This null is aligned with the maximum of the single-beam. This antenna sends a continuous signal (AM modulated tone).

Bernhard beam concept Rotating beacon cartoon

Fig. 2: Concept of the Bernhard/Bernhardine radio-navigation system


The "Bernhardine" Hellschreiber-printer in the aircraft prints two parallel tracks on a paper tape, see Figure 2:

  • The lower track prints the azimuth value of the single-beam signal, as the beam passage illuminates the aircraft during several seconds. This is a two-digit value for every ten degrees of azimuth (as is done to identify the magnetic heading of runways at aerodromes), and a tick mark for each degree. A station-identifier letter is also printed every 10 degrees ("M" in Figure 2). The azimuth (bearing from the beacon) was referenced to True North (QTE, "Rechtweisend"), see §10 in ref. 14, ref. 15, p. 8 in ref. 183. These days, aeronautical radio-navigation beacons are referenced to Magnetic North (QDM; exception: Canada's Northern Domestic Airspace, a polar region).
  • The upper track prints the (clipped) signal strength of the received continuous signal of the twin-beam antenna. Hence, the printed pattern shows the two lobes of that twin-beam, with the sharp null in between. This accurate V-shaped null points at the exact azimuth value that is printed in the lower track.
  • The paper tape only moves when a sufficiently strong signal is received (typ. 3-5 sec per revolution of the beacon). So, the print-out does not need to be interpreted immediately.

To the best of my knowledge, no original "Bernhard" audio recordings exist today. So I have simulated the sound of a transmission. The recording below comprises two beam-passages: once without the information in Hellschreiber-format (i.e., only the constant 1800 Hz tone), and once the constant tone plus the constant stream of 2600 Hz Hellschreiber-pulses.


Bernhard sound

Simulated sound of two "Bernhard" beam-passages - without & with Hellschreiber tone pulses



Unlike typical radar systems, "fighter guidance" navigation beacons such as Bernhard-stations were only operational on demand. E.g., around the Allied invasion of Normandy on 6 June 1944 ("D-Day", "Operation Overlord"), the British observed the Bernhard station at Le-Bois-Julien (France) with a 10 cm (3 GHz) radar in East Sussex: no rotation on June 1st, 6th, 7th, and 9th. The antenna rotated for a period of 2 hours 20 min during night of June 2nd, 4 hours 20 min during evening of June 3rd, 4 hours + 1 hour 25 min + 20 min during the early morning and early evening of June 5th, 2 hours 50 min late afternoon of June 8th. Ref. 173A.

The "Bernhard/Bernhardine" system is the final evolution of the Telefunken Rotating Beacon system. The remainder of this page describes the historic background of such radio navigation beacons, starting with the original invention during the early 1900s, and the subsequent development phases leading up to the "Bernhard/Bernhardine" system in 1941. A summary of other German beam systems is provided at the end.

The British and US military and intelligence referred to this system as "Windjammer" (p. 4.09 in ref. 13, ref.172, 173, 174).


TELEFUNKEN ROTATING-BEAM BEACON SYSTEMS FOR RADIO-NAVIGATION

Rotating-beam radio-navigation beacons are the radio equivalent of common optical rotating beacons: lighthouses. In 1908, Austrian-born Alexander Meißner (sometimes spelled Meissner) invented a rotating-beam beacon: the "Kompass Sender" (lit. compass transmitter). Ref. 185, 186, 187. He also pioneered transmitters using radio tubes/valves instead of mechanical generators or spark-gaps, and invented the feedback-based oscillator around the same time (1912/13) as Lee de Forest, E. Reisz, C.S. Franklin, H.J. Round, E.H. Armstrong, and I. Langmuir.  The "Kompass Sender"  was developed by the Telefunken company, and used for long-range navigation of Zeppelin dirigibles (ref. 1, 2, 16, 17A, 18). A complete network of these beacons was already foreseen in 1912 (ref. 187).

The antenna system comprised 18 dipoles  of 2 x 60 m, and a motorized antenna switching system. The dipoles were arranged in a star configuration, i.e., one for every 10 degrees. See Figure 3. Individual dipoles were successively connected to the transmitter via a motorized distributor that turned at 2 rpm (1 revolution every 30 sec). The switching sequence created a rotating dipole radiation pattern with a constant signal. Meißner later replaced the rotary switch with a contactless goniometer arrangement. It consisted of a rotating "search" coil that sequentially coupled inductively to the stationary feed-coil of each dipole.

Telefunken Kompass-Sender

Fig. 3A: The array of 18 dipoles and motorized distributor of the "Kompass Sender"


Once per revolution, at the "north" position, the station identifier was sent in Morse code via all dipoles simultaneously (omni-directional). Bearing (azimuth) from the beacon is determined by measuring the time between the "north" marker and passage of signal minimum. This was done with a calibrated 30 sec stopwatch that had a compass rose on the dial. As the radiation pattern of a dipole is shaped like a figure "8", it has two identical minima. Hence, a 180 degree ambiguity. The ambiguity is resolved by determining the bearing from another beacon (triangulation). With the 2 x 60m "half wavelength" dipoles, the spark-gap transmitter generated a signal in the medium wave band (a wavelength of around 240 meter wavelength, equivalent to a frequency of 1250 kHz). "Telefunken Kompaß" is the complete system: "Kompass Sender" beacon + ordinary radio receiver + special stopwatch. It achieved an accuracy of about 3°. The system was operational through the end of WW1 (1918).

Telefunken Kompass-Sender

Fig. 3A: The special 30-sec stopwatch of the "Kompass Sender" system

(source: adapted from Fig. 2 in ref. 187)

By 1934/35, reasonably efficient UHF transmitters had become practical. Therefore, during the spring of 1935, the Telefunken company decided to develop "Telefunken-Drehfunkfeuerverfahren", a new Telefunken rotating radio-navigation beacon system (ref. 181, 183). Construction of a UHF test/evaluation beacon started in August of 1935. It operated at a frequency of 300 MHz (λ = 1 m). It was installed at a Telefunken test site near Groß-Ziethen, just north of Berlin-Schönefeld airfield. These days, the name of the town is spelled "Großziethen", not to be confused with another Groß-Ziethen, 75 km to the northeast. The UHF transmitter had a an output power of 1 watt (ref. 3). The UHF receiver was located on the tower of the nearby Telefunken plant in Berlin-Oberschönweide, about 8 km (5 mi) to the northeast. The output signals from the receiver were fed back to the transmitter site via regular phone lines. In December of that year, the beacon was demonstrated to the Reichsluftfahrtministerium (RLM, the German Air Ministry). The antenna system comprised two array of vertical dipoles, placed in front of a reflector surface (see Fig. 4 below). The two sub-arrays were fed 180° out of phase. This creates a radiation pattern with two slightly diverging main lobes, with a sharp null between them.

UHF beacon

Fig. 4: The UHF beacon at Groß-Ziethen

(source: Fig. 16 in ref. 181)

The test-setup achieved an excellent accuracy of better than 0.1°, based on the received signal amplitudes that were captured with a strip-chart recorder. Fig. 5 shows a plot of the amplitude of the received while the antenna rotates, i.e., while the two lobes of the radiated pattern repeatedly sweep by the receiver antenna. The plot clearly shows the null of each sweep, flanked by the two main lobes of the radiation pattern:

UHF beacon

Fig. 5: Signal-amplitude plot of the Groß-Ziethen beacon - showing deep null of the antenna radiation pattern

(source: Fig. 17 in ref. 181)

Based on the demo, the RLM ordered three prototype beacons in 1936. They were built at the following locations (ref. 181):

  • Rechlin, about 100 km north-northwest of Berlin. The airfield of Rechlin had become an Erprobungsstelle der Deutschen Luftwaffe ("E-Stelle", official Luftwaffe test site, ref. 19). Construction of this beacon started late 1936. Beacon tests were probably conducted by "Abt. F" (Department-F) - "Hochfrequenzforschung und Leitstrahlverfahren" (RF-research and flight guidance beams) of the "E-Stelle".
  • The Telefunken test site near Mietgendorf (near Trebbin and Glau), about 35 km southwest of down-town Berlin. This beacon was constructed during the spring of 1937.
  • On the Wasserkuppe, the highest point of the Rhön mountain range in central Germany. This was a camouflaged beacon. Using camouflage is addressed in the 1936 Telefunken patent 767354 (line 49-57).

X station

Fig. 6: Location of the three 1936/37 UHF test stations

(modern national borders)

UHF beacon

Fig. 7: The beacon at Rechlin (left) and Mietgendorf

(source: Fig. 18 & 19 in ref. 181)

Note that in this generation, the antenna system had been expanded compared to the original system of the beacon at Groß-Ziethen. The latter had two side-by-side sub-arrays of two vertical dipole antennas each (Fig.4 above). However, now, there are two sub-arrays of five vertical dipoles each. This makes the main lobes of the radiation pattern narrower, and the null sharper. Above it is a separate array, also of five vertical dipoles. See the left photo in Fig. 7 above. This upper array generates a radiation pattern with a single main lobe. This lobe coincides with the null between the main lobes of the lower array. The beacon now also has two 20 watt UHF transmitters, one each for the top and bottom array, instead of a single 1 watt transmitter.

UHF beacon

Fig. 8: The camouflaged beacon on the Wasserkuppe

(source: Fig. 20 & 21 in ref. 181)

During 1936/37, flight test were performed by both Telefunken and the "E-Stelle" at Rechlin. The next photo shows an early equipment set, used in the test aircraft for the reception of the UHF beacon signals, and capturing signal strengths with a 2-channel wax-paper plotter.

UHF beacon

Fig. 9: First Telefunken airborne receiver and 2-channel plotter for the UHF beacon

(source: Fig. 22 in ref. 181)

The plotter has to plot two traces, as the beacon now transmits two signals: one via the upper antenna array (single lobe) and one via the bottom array (twin-lobe with sharp null):

Bernhard antenne pattern

Fig. 10: Radiation pattern of the antennas for the pointer signal (lobes D) and the compass scale (lobe K)

(Left: Fig. 2 in patent 767354, right: Fig. 1 in patent 767523)

The single lobe is used to continuously transmit the momentary azimuth value of the antenna's pointing direction (= centerline of the single lobe = null of the twin-lobe). The two signals are plotted simultaneously as two parallel traces. The passage of the null causes a narrow dip in the associated upper trace of the plotter. This used as a pointer ("Zeiger") for the azimuth ("Skala") value information printed in the lower trace.

This is the essence of the Telefunken rotating beacon system!

In this early version of the system, the plotted azimuth trace resembles that of a Morse "undulator" recorder. The transmitted pulses were generated with a optical encoder disk that rotated with the antenna. A simple encoding format was used: a sequence of short and long pulses for every 10° section of each compass rose quadrant. It is basically an adaptation of the numbers 0 - 9 in Morse code. However, here, each individual dot and dash marks 1° of the compass scale. No dash is used for marking 9°, 19°, ... , 89°. The resulting pause is used to identify the start of the next 10° section:

UHF beacon

Fig. 11: Encoding of the compass rose on the optical encoder disk

(source: adapted from Fig. 5 & 6 in the 1936 Telefunken patent 767354)

When the beams of the rotating beacon sweep by and "illuminate" the receiving aircraft, the following 2-trace plot is generated:

UHF beacon

Fig. 12: xxx

(source: adapted from Fig. 4 in the 1936 Telefunken patent 767354)

Note how the signal-strength trace clearly corresponds to the two main lobes D and associated null of the antenna radiation pattern (Fig. 10 above).

An example of an experimental 2-trace plot is shown in the next Figure. It is from a 1937 Telefunken test flight that recorded the signals from the Mietgendorf beacon, while flying near the city of Breslau at an altitude of 4000 m (13 thousand feet). This city is situated about 300 km (190 miles) southeast of the beacon near Berlin. At the time, Breslau was in the Lower Silesia ("Niederschlesien") region of the Reich. After the war, this area (and others) became part of Poland, and the name of the town changed to Wrocław (Wrazlaw). There were two Luftwaffe airfields there: Breslau-Gandau (Junkers aircraft factory, pilot school Flugzeugführerschule A/B 71 added in 1938), and Breslau-Schöngarten (home of Luftkriegsschule LKS 5, "Air War School nr. 5").

UHF beacon

Fig. 13: 2-trace plot of a Telefunken test flight during the summer of 1937

(source: Fig. 23 in ref. 181)

The conclusion from numerous measurements was an achieved accuracy of about ±0.3°, primarily caused by uncertainty about the real position of the aircraft: the accuracy of the "beacon + airborne system" was actually determined to be around ±0.1°. Range with the 20 watt transmitters at 300 MHz was about 300 km (190 miles) at an altitude of 4000 m (13 thousand feet). At lower altitudes, the achieved beacon range was consistent with visual range. Extensive flight tests with the beacon on the Wasserkuppe early 1938 had similar results: range of 270 km at 2000 m, 320 km at 3000 m, and 340 km at 4000m. As shown in Fig. 8 above, the antenna system of the Wasserkuppe beacon was mounted on a tower. Range with the antenna installed closer to ground level (as was the case at Rechlin and Mietgendorf) was about 80 km smaller. The average accuracy was ±0.25°, with outlier cases as high as ±0.5° and one of ±0.75°. Note that the objective was an accuracy no worse than  ±0.1°... These achieved system-level results ( = beacon + radio wave propagation + uncalibrated aircraft equipment) were a very significant improvement in radio direction-finding (RDF) accuracy. The mentioned Telefunken and E-stelle tests confirmed that the performance of the UHF system was unaffected by weather, twilight and night-time effects, and mountain effects. In all, sufficient reasons to further develop the system and introduce it into service.

After the successful proof-of-concept, attention was focused on presenting the bearing (azimuth) value in a form that was directly readable by anyone, and did not require interpretation of a squiggly undulator trace. For the given antenna configuration and dimensions, an accuracy better than ±0.3°was not achievable. Hence, an indicator device did not have to have an accuracy much better than that. This cleared the way for using a 2-channel Hellschreiber-printer instead of a 2-channel strip-chart recorder:

UHF beacon

Fig. 14: First two-trace Hellschreiber print-out on paper tape of the UHF beacon signals - fall of 1937

(source: Fig. 24 in ref. 181)

One-channel Hellschreibers for civil/commercial and military had been around since the early 1930s. It was robust off-the-shelf technology for making a direct-printing system. A Hellschreiber printer comprises an inked spindle that is placed across, and slightly above, a moving paper tape. Below the paper tape is an electromagnet with a hammer blade. When the magnet is energized, the hammer pushes the paper tape against the continuously turning spindle. This causes a line segment to be printed across the paper tape. The length of the printed line depends on the amount of time that the electromagnet is energized. See the "How it works" page. Basically, it prints a line of symbology (text, or - as is the case here - a compass rose scale), that is transmitted to the receiver in the form of a sequence of pixel-pulses. It is similar to a simple fax system that prints a stream of symbols on a paper tape.

The upper trace of the 2-trace print-out is the amplitude of signal received from the twin-lobe transmitter antenna. The transmitter sends a continuous signal, not a pulse stream. A special electronics box had to convert the amplitude of the radio receiver's audio output into a stream of pulses. The width of each pulse represents the momentary signal amplitude, and is printed by the Hellschreiber as a vertical line segment. Hence, the height of this line segment represents the signal amplitude. See the upper trace in the figure above. The special Hellschreiber beacon-printer and associated electronics are described on this page. As the above figure shows, the initial print quality was far from perfect, but it showed that the right solution had been found!

The original 1936 Telefunken patent (767354) mentions the possibility of transmitting the azimuth data via the principles of fax or TV ("Bildfunk oder Fernsehprinzip"). Other early patents are explicitly based on transmission of compass-rose information via video (Nipkow-disk image scanning): e.g., patent 562307 (1929, J. Robinson) and 620828 (1933, Marconi Co.).

During the summer of 1938, the three beacon stations were completely refurbished. The new transmitters had a stable crystal-oscillator instead of a free-running oscillator. The new optical disk (bottom of the next photo, between the two black equipment racks) now had the compass rose symbology captured in Hellschreiber format. All electronic equipment was rack-mounted. The output signals of the two transmitters were transferred to the rotating antenna system via a slip-ring arrangement (top of the next photo).

UHF beacon

Fig. 15: New & improved equipment set for the three beacon stations - summer of 1938

(source: Fig. 25 in ref. 181, also p. 95 in ref. 3)


In these UHF installations, the transmitters did not rotate with the antenna system: they were located in the small stationary building below the antenna system. This arrangement requires a rotary coupler between the antenna system and the transmitters. This may have been implemented as a set of slip-rings on the shaft of the rotating antenna system. Note that a slip-ring approach ("HF-Schleifringkopplung") was actually used in several German systems, for instance the FuMG 404 "Jagdschloß" radar (designed by GEMA, built by Siemens). Ref. 151. The largest version had a 24 m wide array antenna system (4 x 16 horizontal dipoles) that weighed 25-30 metric tons. It rotated at 10 rpm, with the central shaft driven by a 75 kW 3-phase motor. It was a UHF system (120-240 MHz, depending on the version). It transmitted 1- 2 μsec pulses of 8-20 kW, with a pulse repetition frequency (PRF) of 500 / 3000 Hz.

However, there is also a 1936 Telefunken patent (nr. 767525), by Adalbert Lohmann. He was Telefunken's expert on rotary navigation beacons, including the Bernhard system. This patent is explicitly for the directional antenna system of the Telefunke rotating beacon station. It proposes a method for a contact-free rotary coupler: no contact resistance, no arcing at brushes! The coupler comprises two sets of stator and rotor disks that form capacitors. See Figure YYY. The disks are installed coaxially: the rotor plates are fixed to a rigid shaft (preferably ceramic), the stator plates to the housing of the coupler. The transmitters are wired to the edge of the respective stator plate. Note that in the VHF (30 MHz) Bernhard system, the transmitters are located on the same rotating platform as the antenna system. Hence, no rotary couplers were required for between the transmitters and the antennas. Of course, in this configuration, electrical power for the transmitters must be provided via slip-rings.

Bernhard antenna system

Fig. YYY: Contact-free rotary coupler for RF signals

(source: the 1936 Telefunken/Lohmann patent 767525)


The equipment set for the aircraft was also completely redesigned - and doubled: two receivers, and the Hellschreiber printer (and associated electronics) had four channels.

UHF beacon

Fig. 16: New & improved aircraft equipment - summer of 1938

(source: Fig. 26 in ref. 181)

With a single beacon, only relative bearing to/from that particular station can be determined. I.e., a position line ("Standlinie"), and neither distance (range) from the station nor a position point. Position determination is done by combining the bearing from at least two beacons with known location. I.e., by means of conventional triangulation ("Kreuzpeilung"). Note that the bearing from a ground station to the aircraft should not be confused with the aircraft's heading (the way the nose is pointing), nor with the aircraft's course (ground track).

Triangulation

Fig. 17: Triangulation with two ground stations

(D = beacon ("Drehfunkfeuer"), α = azimuth = bearing from station = angle measured clockwise from north)

The new dual equipment allowed printing of the signals from two beacons simultaneously onto a single, extra wide strip of paper. I.e., do triangulation without having to switch back and forth between two beacons. This is covered by Lohmann/Telefunken patents 767937 and 767538. Assuming simultaneous reception of two beacons, the aircraft's position (and, hence, its ground track) could be sampled and recorded continuously.

Triangulation

Fig. 18: Sample of a print-out ("Registrierungschrieb") from the dual receiver-printer system during UHF tests

(source: Fig. 27 in ref. 181; also used in ref. 3; also see patent 767537)

The upper traces of the above plot show that the aircraft is on a bearing of 239° from beacon "R", and on a bearing of 315.5° from beacon "M". Note that, compared to the initial experimental Hellschreiber print-out (Fig. 14 above), the compass rose track now includes the identification letter of the beacon: "R" = Rechlin, "M" = Mietgendorf, "W" = Wasserkuppe. Lighthouses for nautical navigation are identified by the blinking pattern of their light beam. Here, a letter is transmitted every 10 degrees of the compass rose.

In Hellschreiber-format, any graphical information that is to be transmitted, is decomposed into a number of consecutive pixel columns. A 360-degree compass rose comprises a band of tick marks and numbers. This band can be converted to Hell-format by decomposing it into columns of pixels as shown in Figure 19B below. Consecutive columns are transmitted pixel-by-pixel, top-to-bottom. For details, see this page.

Patin remote compass

Fig. 19A: Remote compass, as used in Fw190 etc.

(made by A. Patin & Co. G.m.b.H. of Berlin)

Bernhard compass card

Fig. 19B: Compass rose of the Telefunken system

(sources: patent 767524 (top), ref. 15 (bottom))


Note that the compass scale shows a one- or two-digit value for every ten degrees of azimuth. That is 1 - 36 for each multiple of 10 degrees (10° - 360°). This is also the standard format for compass roses in general, and for identifying the (magnetic) heading of runways at aerodromes (so there is no runway nr. 0, or a runway with a number larger than 36 - other than in stupid movies). The scale has a short tick mark for each degree, a medium size tick mark for each five degrees, an along tick mark for the each 10 degrees. The azimuth (bearing from the beacon) was referenced to True North ( = QTE), see §10 in ref. 14 and ref. 15. These days, aeronautical radio-navigation beacons are referenced to Magnetic North ( = QDM; exception: Canada's Northern Domestic Airspace, a polar region).

I have used FontStruct™ to capture the above signal-level track and compass-rose segment as Feld-Hell character of a "TrueType" font that can be used in regular Windows® and MacOS® programs (e.g., Word®, PowerPoint®). Click here for the two-character font (capital letters A and B) for the signal level. Click here for the 18-character font (capital A-R) for the 360º compass-rose.

":Bernhardine" compass card

Fig. 20: Re-created signal strength bar graph, azimuth data, and station identifier "M"


A station-identifier letter is also printed every 10 degrees (e.g., "R" and "M" in Figures 18, 19B, and 20 above). The Hellschreiber printing system was the world's first application of a bit-map font. The printer itself is totally oblivious to the content of the bit-pattern. It simply prints each pixel that it receives. This made it possible to temporarily transmit short text messages of 10 characters, instead of the compass scale. For details, see this page. The was the world's first textual command-uplink system! The messages followed the same format as fighter-control "Reportage" messages, that were normally broadcast via Morse code telegraphy and radio telephony (which was also subject to jamming). This also freed up radio-telephony capacity. Implementation of this data link system required a modification to the beacon, and was only implemented at two or three stations by the end of the war.

Bernhard reportage track

Fig. 21: re-created Bernhardine print-out with "Reportage" track instead of compass scale


Late 1938, all prototyping and concept validation-testing was completed. This allowed the RLM during the spring of 1939 to decide to implement the system. However, the activities (incl. construction of beacons) were interrupted for two reasons: the outbreak of the war during the fall of 1939, and the conclusion that the scope of the program (i.e., final development of beacons and aircraft equipment) was too big for the expected scale of this war. Only the pre-production development was to be completed, just in case the need would arise. E.g., the successful dual receiver/printer equipment of 1938 lacked two features. automatic gain control of the received beacon signals, and automatic start-stop of the printer. The latter was needed, as the printer could only include a limited supply of paper tape, a beacon was only received during several seconds of each 30 sec revolution its antenna, and the printed signals should remain visible long enough so as not to require immediate interpretation by the navigator/operator. The required design enhancements were completed during the spring of 1940:

UHF beacon

Fig. 22: The automatic receiver/printer system - early 1940

(source: Fig. 29 in ref. 181; also p. 97 in ref. 3 and Fig. 29 in ref. 92)

To make the automatic receiver/printer work properly, the beacon also had to be adapted. In particular regarding the minimizing the side-lobes of the antenna's radiation pattern. Significant effort was expended to arrive at the final solution: a parabolic antenna with an aperture of 6 λ (where wavelength λ = 1 m as f = 300 MHz), a focal length of 5/4 λ, and two dipole feed-antennas (one for the compass rose signal, one for the pointer signal). However, this antenna configuration caused undesirable coupling between the transmitted signals. To suppress this without compromising the complicated radiation patterns, the transmitters were mounted on the back of the rotating antenna (see the right hand photo in Fig. 23 below). I.e., not in the stationary base of the antenna, with connection to the antenna via a slip-ring assembly. Two beacons were constructed. One was again built at the Telefunken test site near Mietgendorf. The other at the Kriegsmarine naval station of Schillig, just northwest of Wilhelmshafen (a major Reichskriegshafen). By the summer of 1940, the evaluation tests were so successful, that the pre-production development of the complete UHF rotary beacon system was concluded.

UHF beacon

Fig. 23: the new beacon at Mietgendorf (left) and at Schillig (note box with transmitters on the back of the antenna)

(source: Fig. 30 & 31 in ref. 181)

Thus far, the achievable performance of the Telefunken system had been established at UHF operating frequencies. However, for long-distance navigation, a system with a much larger range (500 to several 1000 km) would be needed. The concept of the Telefunken system During the second half of 1940, a rotary beacon was built to investigate the performance on shortwave frequencies. I.e., on HF instead of UHF. As already mentioned, UHF radio waves basically propagate along the (straight) line-of -sight. On HF, however, radio waves to some extent follow the curvature of the earth ("groundwave"), and are also refracted by the ionosphere. The ionosphere is a part of the upper atmosphere. It has layers of atoms and molecules that are ionized by solar and cosmic radiation, as well as by high-energy charged particles from space. HF radio waves may actually make multiple "hops" between the earth's surface and the ionosphere, and propagate much farther than the groundwave. This depends on the altitude, thickness, and density of the ionized layers, as well as the angle at which the radio waves ("skywave") enter the ionized layer(s). The characteristics of the ionosphere are subject to daily and seasonal cycles, as well as the 11-year sunspot-cycle. 

In order to assess the feasibility and accuracy of an HF rotating beacon system, Telefunken built a test beacon in a field just outside Großbeuthen. This is a village about 3.5 km (≈2.2 mi) east of the Telefunken site near Mietgendorf, where one of the UHF beacons had already been tested. Two receiving stations in occupied France were used - one at Dieppe (at 900 km from the beacon), and one at Morlaix (1300 km from the beacon):

Berhard station

Fig. 24: HF beacon at Großbeuthen, monitoring receivers at Dieppe & Morlaix

(source: adapted from Fig. 33 in ref. 181)

The above map shows that  receiving stations are on the same bearing (azimuth) from the beacon. This helped assessing the reception results, as they received the beacon signal simultaneously, i.e., under the same radio wave propagation conditions, and their Hellschreiber printers should record the same compass rose values.  

The new beacon was given the code name "Haubenlerche" (lit. “crested lark”, a bird). Its antenna system comprised two parallel vertical dipoles. . Three operating frequencies were used: around 11 MHz (wavelength λ ≈ 27 m), 7.5 MHz (λ ≈ 40 m), and 5.5 MHz (λ ≈ 54 m). As these frequencies are much lower than the 300 MHz (λ = 1 m) of the tested UHF beacons frequencies, the dipoles are correspondingly longer. The dipoles are installed such that their bottom tip is at a height equal to about the length of one dipole "leg" (≈ 1/4 λ). This reduces the impact of the soil on the radiation pattern. The dipoles are spaced by about their tip-to-tip length (i.e., ≈ 1/2 λ).

UHF beacon

Fig. 25: The "Haubenlerche" beacon near Großbeuthen

(source: Fig. 35 in ref. 181)

The transmitter was located in the octagonal room directly below the antenna mast. This room rotated with the antenna. This arrangement avoided errors that would be otherwise introduced by using a slip-ring between a stationary transmitter and the rotating antenna. The motor drive for rotating the "antenna + transmitter room" was located in the slightly larger octagonal room below it. The entire structure sits on top of a round brick building with four corner pillars.

The beacon had one transmitter, with an output power of 500 watt. Only the constant pointer-signal was transmitted, as it is most critical for the system accuracy.

UHF beacon

Fig. 26: Radiation pattern of a single vertical dipole vs. 2 vertical dipoles, spaced 1/2 λ and fed in-phase


Extensive tests were run during a 4-week period in the winter of 1940. In all, bearing values were measured well over 23 thousand times! Only in about 1% of the cases were the bearing values recorded by the two receiving stations identical (both the sign of the error with respect to the actual bearing, and the width of the V-shaped pointer as printed by the Hellschreiber recorders). About 60% of the data was unusable, as the received signal strength was insufficient - not too surprising, given the transmitter's output power. Of the 40% usable data points, all had an accuracy better than ±4°, 97% better than ±3°, 83% better than 2°, and 58% better than 1°. Note: at range of 1300 km, 1° is equivalent to ≈23 km.

UHF beacon

Fig. 27: The V-shaped pointer as printed by the Hellschreiber recorder under various radio-propagation conditions

(source: Fig. 34 in ref. 181)


The round brick building of the "Haubenlerche" beacon is still standing today (2017, compare to Fig. 25 above in 1940):

Berhard station

Fig. 28: The "Haubenlerche" brick building, just south of Großbeuthen - over 75 years later...

(source: ©2017 B. Saalfeld; used with permission)

Berhard station

Fig. 29: The "Haubenlerche" brick building, just south of Großbeuthen

(source: ©2016 B. Saalfeld; used with permission)

Its roof has a diameter of about 6 m (≈20 ft). The inside diameter of the building is 4 m (≈13 ft), with a wall thickness of 40 cm (≈16"). The floor-to-ceiling height is 2.7 m (≈9 ft). It has four support columns (that appear to be brick, rather than steel I-beams), three windows, and a brick wall. The roof is reinforced with four sections of steel beam that join at the center of the roof. There is no hole at the center of the roof, to the equipment room and antenna installation on top of it. The door opening is 1.9 m tall and very wide. The floor inside the building is at the same level as the ground outside. According to an eyewitness account, there still was an "installation" on the roof, shortly after the war (WW2).

Berhard station

Fig. 30: The inside of the brick building

(source: ©2016 B. Saalfeld; used with permission)

Berhard station

Fig. 31: The door opening of the brick building

(source: ©2016 B. Saalfeld; used with permission)

On top of the roof, there is an octagon (about 2.6 m across) that is made of crudely cemented bricks. One side of the octagon is open. At each corner, there is a heavy mounting plate with bolts sticking up, for an 8-legged superstructure. Two steel plates protrude from the center of the roof.

Berhard station

Fig. 32: Octagonal structure on top of the roof - satellite image at right

(source: ©2016 B. Saalfeld; used with permission)

There are two pairs of metal conduits that enter the building near ground level. One has the remains of a multi-strand cable with aluminium wires.

Berhard station

Fig. 33: 2x2 cable entries, including a multi-strand aluminium cable

(source: ©2016-2017 B. Saalfeld; used with permission)

A slightly smaller and heavily reinforced version of this round brick building was used as the equipment room and central support of the "Bernhard" VHF beacon ground station (see next section). Note that the gauge (diameter) of all wiring of the "Bernhard" beacon was explicitly based on aluminium wiring (ref. 189).


DEVELOPMENT OF THE VHF TELEFUNKEN "BERNHARD/BERNHARDINE" SYSTEM

Late 1940, British interference with the Knickebein beam system became increasingly successful. This led to the demand from the German military for rapid replacement of the Knickebein system. The new system had to be more universal ( = general navigation), more robust to interference, and with "maximum" range (p. 70, 71 in ref. 181). The solution was the Telefunken Rotating Beam system. First of all, such a continuously rotating beam could be used for navigation tasks other than identification of a bombing target with stationary-but-adjustable beams. Secondly, the electronics between the radio receiver and the Hellschreiber printer had narrow audio-tone filters. They provided selectivity that made it harder to block reception. Jamming transmitters of much higher power were needed to make the system unusable, and could also not spoof the system (i.e., cause it to generate false bearing indications).

Fast implementation of the new beacon system required the use of:

  • aircraft radios that were mature and already in service in large numbers. I.e., no development of UHF radios and antennas for the aircraft. Instead, use the same 30-33.1 MHz (λ ≈ 10 m) beacon receivers as with Knickebein - without any modifications.
  • Note that at this time, there were no UHF aircraft receivers that were "production ready".
  • This meant changing the operating frequency of the rotating beacon system from UHF ("1 m") to low-VHF ("10 m"). Hence, significantly increasing the size of the antenna system, and not using a dish antenna but arrays of vertical dipoles. Note that this does not change the actual concept of the Telefunken system.
  • Using existing radios was so eminently important, that the implications for the ground station was gladly accepted - as it had been for Knickebein. Also, development of the Knickebein had been a good exercise in mechanical engineering for constructing a large continuously-rotating antenna system.
  • As had been demonstrated with Knickebein, the range of a "10 m" system could be significantly larger than that of the UHF beacons.
  • transmitters that were available off-the-shelf in sufficient numbers. This was no problem, as 30-33.1 MHz beacon transmitters were readily available. Also, for this frequency range, multi-kW AM transmitters were state-of-the-art. For 300 MHz, however, there were no reliable transmitters with more than 200 watt output power.

Note that at the time, Telefunken considered the "10 m" solution as an absolute "Kriegsnotlösung" (p. 18 in ref. 183): a significant compromise, undoubtedly correct for furthering the war cause, but not for a post-war solution. Obviously, the latter consideration was irrelevant under the given circumstances.

So, after about one year of interruption, the development of the Telefunken rotating beam system was resumed. The beacon station itself was given the code name "Bernhard" and the military designator FuSAn 724. Here, "FuSAn" stands for "Funksendeanlage": a radio transmitter installation, incl. the antenna system. The Hellschreiber printer system for the aircraft was named "Bernhardine", with the designator FuG 120. "FuG" stands for "Funkgerät", i.e., radio equipment. This is typically a transmitter and/or receiver, with antenna and installation rack. However, here it is used in the sense of an add-on to a radio set. The numbers 724 and 120 have no specific meaning. They are just entries in a running numbering system.

Note that by the time that the first VHF Bernhard/Bernhardine system became operational, the focus on the western front (Britain) had already shifted to (night-) fighter control (i.e., defensive), rather than for guiding bombing missions over enemy territory (i.e., offensive). The latter had moved to the eastern front (Russia).

The following diagram summarizes the time-line of the end-to-end development and operation of the various implementations of the Telefunken rotating beam system. It spanned a full decade:

Bernhard development time-line

Fig. 34: Time-line of the development and deployment of the Telefunken rotating beacon system

(based on ref. 3, 181, 183)


CHARACTERISTICS OF THE FuSAn724/FuG120 "BERNHARD/BERNHARDINE" SYSTEM

Basic characteristics of the Bernhard/Bernhardine system are:

  • Frequency: 30 - 33.1 MHz.
  • Transmitter power: 2 × 500 watt (FuSAn 724)
  • There are references to a high-power version of the "Bernhard station": FuSAn 725, with 5000 watt transmitters. There is no evidence that these transmitters were ever developed and entered into service. Ref. 20 and 21 state that they were planned only.
  • The wiring list of the "Bernhard" station contains several items with two gauge specifications: one for a 500 W transmitter, an a much heavier gauge for a 4000 W transmitter (cables nr. 6-8, 33, and 34, in ref. 189).
  • Antenna system dimensions: ≈28 x 35 m (HxW, 92x115 ft).
  • Rail track diameter: 22.6 m (74 ft).
  • Weight of the rotating construction: 120 tons (265000 lbs), ref. 21, 181, 183; some literature states the weight as 102 tons (ca. 256000 lbs) which is probably a typographical error, or 100 tons (ref. 20).
  • Antenna rotational speed: 12 degrees per second (2 revolutions per minute). This means that the small locomotives that turned this enormous antenna installation, moved at a respectable speed of 8.3 km per hour (5.2 mph). Justification for selecting this particular speed is given here. The speed was kept constant to within about ±0.2 % (!) Note that by design, the printer in the aircraft can not work with a beacon that turns at a different speed.
  • Accuracy: initially ±1°, then improved to ±0.5°, finally reduced to ±4° by using a single-trace ( = simpler) printer system and a single transmitter (though unclear if this was ever operational).
  • Operational range as a function of aircraft altitude (with respect to the "Bernhard" antenna altitude):

Bernhard system range vs. altitude graph

Fig. 35: Operational range of the Bernhard/Bernhardine system vs. aircraft altitude

(source: based on data in ref. 15)

The above graph is based on a table in the official "Bernhardine" manual (p. 22 in ref. 15). The beacon is assumed to be at zero altitude. Note: as FuSAn 725 never entered service, the claimed range was obtained with 500 W transmitters of FuSAn 724. This range makes "Bernhard/Bernhardine" a medium-range system, like other Luftwaffe radio-navigation systems such as "Erika", "Erich", "Hermine", and "Mond" (ref. 22).


Berhard station

Fig. 36: "Bernhard" beacon nr. 10 (Be-10) at Hundborg/Denmark

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

For design, construction, and functional details of the "Bernhard" ground station, see the FuSAn 724/25 "Bernhard" page.


The British and US military and intelligence referred to this Radio Direction Finding (R.D.F.) system as "Windjammer" (ref.172, 173, 174). By mid-1943, they basically had the system construction and operating frequencies figured out correctly. Ref. 712 A. However, a 1945 US "Intelligence" synopsis of the "Bernhard/Windjammer" system (p. 4.09 in ref. 13), confuses it with the "Y-System" ("Benito"), even towards the end of WW2. Contrary to the Bernhard system, the Y-System could provide "slant range", i.e., line-of-sight distance (not distance-over-ground) between the aircraft and the ground-station. The referenced frequency also belongs to the "Y-System" (42-48 MHz), not the Bernhard system (30-33.1 MHz).

Bernhard description US
Bernhard description US

Fig. 37: Flawed 1945 U.S. description of the "Bernhard" system

(source: ref. 13)


The FuG120 "Bernhardine" system comprised the Hellschreiber model HS120, tone-filter unit (SG120, item nr. 3 in the photo below), printer-amplifier unit (SV120, item nr. 4), and a DC-DC power converter unit (U120, item nr. 5). For details, see the FuG120 "Bernhardine" page. FuG120 used the existing "EBl3" landing-beacon radio receiver in the aircraft (item nr. 1). When the FuG120 was in use, the SV120 amplifier unit controlled the RF gain of the EBl3 (hence the cable between the two sub-systems in the photo below).

FuG120

Fig. 38: Instrument racks with the EBL3/EBl2 radios (left) and the FuG120 "Bernhardine" (right)

(source: Fig. 6 in ref. 183, also Fig. 39 in ref. 183)


SOME OTHER GERMAN/LUFTWAFFE BEAM SYSTEMS

Clearly, Bernhard/Bernhardine is a "beam system" for aircraft guidance. The origins of such systems date back at least to the early 1900s, when Otto Scheller of the Lorenz company invented the "Wireless course indicator and telegraph" system (Imperial Patent nr. 201496 of 17 March 1907; also consider nr. 192524 of the same date), ref. 184. At that time (before the widespread advent of aviation), the system was intended for guiding ships. The ground-station of the Scheller system had a radiation pattern with four main lobes in fixed orthogonal directions. See Figure 39. Two of the lobes transmitted the Morse letter "N" (dash dot), the other two the letter "A" (dot dash). Where lobes overlap and are of equal strength, the combination of "A" and "N" results in a constant tone signal (D: "Dauerton"): the "equi-signal". This signal had a beam width of about 1-5°. This was the first "A/N" system, later used in several other Lorenz radio-navigation systems. Later variations of this scheme used narrow "A" and "N" beams, with a much narrower overlap, allowing more accurate determination of the course line of the equi-signal.

Lorenz-Schiller A/N system

Fig. 39: The Lorenz-Scheller A/N system

(the Scheller patent is not based on two crossed loop antennas (above), but two pairs of vertical antennas)

During 1932/33, Ernst Kramar of the Lorenz company applied the concept of the Lorenz-Scheller A/N-system to a "blind landing system" for aircraft. Ref. 28, 29, 30, 188. Note that "blind landing" is a misnomer, as the system did not provide precision vertical guidance down to the actual landing. Hence it is only an approach-beacon (D: "Ansteuerungsfunkfeuer", AFF). These days, we would refer to this beacon as a non-precision "localizer" approach system: the horizontal (lateral) component of an Instrument Landing System (ILS).

Rather than using the Morse letters "A" and "N", this system used "E" (= "dot") and "T" ( = "dash"), which has the same effect but is simpler to implement. The antenna system was simple: a vertical dipole, with a vertical reflector to the left and to the right, at a distance of ¼ λ. See Figure 40. This was patented in 1932 (Reichspatent 577350). Kramar's 1937 patents expand this with a complementary-keyed (e.g., E/T) beam system for vertical guidance. This was simply re-patented in 1940 in the USA by others.

Lorenz-Schiller A/N system

Fig. 40: The Lorenz-Scheller A/N system ("Lorenz Beam") and associated antenna arrangement

(source: ref. 31)

Lorenz-Schiller A/N system

Fig. 41: The Lorenz-Scheller A/N beacon ground station

(source: image left - ref. 31, image right - ref. 144)

The reflectors were activated alternately, to deform the dipole beam slightly to the right and to the left. This effectively created a directional beacon ("Richtfunkfeuer") with a twin-beam radiation pattern. At the centerline of the beams (aligned with the centerline of the runway), the "E" and "T" beams would merge into an 1150 Hz equi-signal zone that had an aperture of 5 degrees. The antenna system was located at the far end (departure end) of the runway, so as to provide left/right guidance throughout the entire approach. During approach for landing, the arriving aircraft would intercept and track the equi-signal beam. The beam-system operated at frequencies in the 30 - 36.2 MHz range (λ ≈ 10 m). The pilot would hear the E/T audio signals, and also have a Left/Right course deviation indicator. At two fixed distances from the runway, a marker-beacon ("Einflugzeichenbake", EFZ-Bake) was installed. An Outer Marker ("Vor-EFZ") at 3 km, and an Inner Marker ("Haupt-EFZ") at 300 m, ref. 32. These beacons transmitted upward at 38 MHz, with a fan-beam. This allowed the pilot to determine when to initiate decent to the runway from a standard altitude and with a standard descent rate (3 degrees flight path). Ref. 17A/B/C, 26B. This "Lorenz beam" system entered service with the German national carrier, the Lufthansa, in 1934 and was then commercialized worldwide. In the UK it became the "Standard Beam Approach" system. By 1938, some 38 of these beacons were installed at airports throughout the German Reich. The above beacon provides lateral (horizontal, left/right) guidance. In 1937, Lorenz/Kramar created a separate system for providing vertical approach-to-landing guidance, by turning the antenna system 90 degrees and placing it next to the runway, abeam the touch-down point. The combined system with lateral- and vertical-guidance beams is called Instrument Landing System (ILS). It is used to this day.

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

Plendl's concept used two directional beacons, sufficiently spaced apart, crossing each other at the target. Plotted on a chart, the two beam lines form a big "X". Hence, this concept was referred to as the "X-Method" ("X-Verfahren"). The aircraft would intercept and track the E/T equi-signal of a director-beam ("Leitstrahl") to the target. A second beacon would transmit three E/T beams that would cross the director-beam at certain distances just before reaching the target. Upon reaching the first cross-beam, the aircraft had to well established on the equi-signal course-line. Reaching the centerline of the second and third cross-beam was used to determine when to release the bombs. This was done with a special stopwatch, the "X-Clock" ("X-Uhr"), see Figure 42B. This mechanical calculator computed the "bomb release" time, based on actual groundspeed towards the target (derived from the times between the cross-beams), release altitude, and type of bomb. In a simplified version, only a single cross-beam was used. Ref. 85C.

The (lead) aircraft required an "X-Equipment" ("X-Gerät") installation. This comprised (see p. 106 in ref. 2):

  • two dedicated receivers with associated rod antennas,,
  • two AFN2 ("Anzeigegerät Flug-Navigation") course-deviation indicators (Figure 42A). The vertical course-deviation needle of this indicator pulsed to the left or right, in the rythm of the dominating "E" or "T" signals ("Zuckanzeige", "kicking meter").
  • an AVP unit ("Anzeige-Verstärker Plendl", "Plendl-method Indicator Amplifier") for each AFN2.
  • a power converter unit and a power-distribution unit,
  • an "X-Uhr" multi-stopwatch bomb-release timer (Figure 42B).

AFN2 indicator

Fig. 42A: AFN2 Anzeigegerät für Funk-Navigation - Left/right course deviation indicator

(the horizontal needle is a signal-strength indicator, as a simplistic near/far distance indication; the indicator lamp in the center is illuminated when receiving a marker beacon during approach)

X-Uhr

Figure 42B: an X-Uhr "Bombenabwurfautomat" (automatic bomb-release timer/computer)


Proof-of-concept was done with "Lorenz Beam" systems. However, these commercial systems had neither the required range, nor the required accurate and narrow equi-beam (±0.1º aperture). Therefore, the operating frequency was increased from 30 - 36.2 MHz to the 66 - 77 MHz range, and the beacon was equipped with more powerful transmitters. The German codename for the "X" ground-station ("X-Station", "X-Bodenstelle", "X-Peiler", "X-Bake") was "Wotan I". The basic antenna system comprised two vertical dipoles. The antenna system as such was rotable to the desired beam direction, but not (continuously) rotating. One dipole was energized continuously with an AM carrier that was modulated with a 2000 Hz tone. The second dipole, placed at a distance of 3½ λ, and energized via a motorized capacitive phase-shifter. The phase was changed stepwise, every 0.5 sec. The resulting radiation pattern had 14 or 18 E/T-beams of about equal strength and an equi-signal zone with a width of less than ±0.1º. The large number of major lobes was very awkward: the aircraft had to fly across the lobes, and count the passages of the "T" zones to find the intended guide beam ("Marschleitstrahl", the 7th of 14 (as in Figure 43 below), or the 9th of 18).

Wotan I beacon pattern

Fig. 43: Radiation pattern of the Wotan I beacon

(source: adapted from ref. 2)

The complexity of the method required extensive pilot training. Only a rather limited number of aircraft was equipped with the X-Gerät. To cope with jamming by the British, the system was modified to use more frequency channels, and a tone modulation well above the standard audio bandwidth of regular receivers. This provided some temporary relief from the jamming. The "Battle of the Beams" between Germany and Britain took place from late-1939 through mid 1941. Ref. 8, 28, 34, 35, 36, 37, 38. During this period, the British developed countermeasures to German radio-navigation systems and radio-telephony communication of fighter/bomber control systems, to which the Germans responded with modified or new systems.

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

The Telefunken company had already been tasked early 1939 to develop a simple beam system that was compatible with the Lorenz Funklande Empfangsanlage Fu Bl 1 ("blind approach & landing system") that was standard equipment in Luftwaffe aircraft (ref. 32). The receivers had much higher sensitivity than required for operation with a landing beacon, to enable long-range navigation. This new system was also an E/T beam system, and also used two crossing marker-beam beacons. Telefunken's extremely rapid development was headed by Adalbert Lohmann, who later headed up the development of the Bernhard/Bernhardine system. The new system operated in the 30-33.3 MHz band, i.e., a wavelength of 9 - 10 m. Obtaining a sufficiently narrow equisignal-beam at these frequencies required an antenna system with two large dipole arrays. The ground stations of this directional-beam system ("Richtfunkfeuer") were Telefunken Funk-Sende-Anlage ("radio transmitter installation") FuSAn 721. Their German codename was "Knickebein".

By the end of 1939, three Knickebein installations were operational along the western border of Germany: Stollberg/Bredstedt on the North Sea coast in the far north (later the location of a Bernhard station), Kleve (Cleves, where the Rhine river crosses into the Netherlands), and Lörrach/Maulburg (in the far southwest of Germany, near the German/Swiss/French border). These were installations with an enormous rectangular antenna system, see Figure 43. Its truss frame measured ca. 90 x 30 m (WxH). Suspended in the frame were two dipole arrays, one for the "E" beam and one for the "T" beam. Each of these sub-arrays comprised 8 vertical wire-dipoles. Each wire-dipole had a dipole-reflector. The system could be rotated on a circular track, to point the beam at the target (in Britain). To obtain a narrow equi-beam (±0.3º), the "E" and "T" beams were offset 7.5 degrees to the left and to the right of the desired equi-beam. This was done by angling the left and right hand half of the antenna system by 15 degrees from each other. Looking at the antenna system from above, it had a slight V-shape ("crooked leg", "dog leg") of 180 - 15 = 165 degrees.

Knickebein large & small

Fig. 44: Knickebein ground-station - large (left) and small (right)

(source: Fig. 36 & 37 in ref. 181; red circle shows the size of a man)


Knickebein pattern

Fig. 45: Radiation pattern of the Knickebein beacon


After the invasion of their neighbor countries, the Germans installed another nine Knickebein stations along the coasts of Norway (1x), The Netherlands (2x), and France (6x, from the Channel coast down to Brittany). Construction of a tenth station in Italy was never completed. However, these stations had a smaller antenna system: about 1/4 the size of the Large Knickebein. The Small Knickebein had a width 45 m, a track diameter of 31 m, and had 2x4 dipoles plus reflectors per beam, instead of 2x8. Hence, the width of the equi-beam was larger (±0.6º). On the other hand, they were installed closer to the targets in Britain than the large stations in Germany. In September of 1941, the aircraft receivers were upgraded from FuBl 1 to FuBl 2, which supported a large increase in the number of available frequency channels in the same band, and a range of 600 km at 6000m altitude (20 thousand feet). During the winter of 1940, the Knickebein system became increasingly unreliable and unusable over Britain, due to jamming by the British. It continued to be used for navigation towards the target, but relied on the X-System (described further below) in lead aircraft ("Pfadfinder") to locate and mark the actual target.

AFN1 indicator

Fig. 46: AFN1 Anzeigegerät für Funk-Navigation - Left/right course deviation indicator of the FuBl 1 system


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

The (lead) aircraft required a "Y-Equipment" ("Y-Gerät") installation (ref. 2, 39). This comprised:

  • one dedicated beacon receiver: the "UKW Leitstrahlempfangsgerät" FuG28a. It that combined a FuG17 radio-telephony transceiver (42.15 - 47.75 MHz, 10 Watt) and an AG28 "Auswertegerät" - an electro-mechanical equivalent of the X-system's AVP unit,
  • an LKZG ("Leitstrahl-Kurststeuerungs-Zwischengerät") to interface the FuG28a to the lateral-axis auto-pilot ("Kursregler"), for automatically tracking an equi-beam,
  • one AFN2 ("Anzeigegerät Flug-Navigation") course-deviation indicator,
  • one FuG16ZE or FuG16ZY transponder (respectively 38.5-42.3 MHz and 38.4 - 42.4 MHz, ref. 40, 41),
  • associated power converter units,
  • various control panels.

FuG17 + AG28a

FuG17 (left) + AG28a (right)

FuG17 + AG28a

Bottom of the unit

Fig. 47: FuG28a "UKW Leitstrahlempfangsgerät" (VHF guide-beam receiver)

(source: www.cdvandt.org)

The "Y-Station" ground station ("Y-Bodenstelle", "Y-Peiler", "Y-Bake") was called "Wotan II" (FuSAn 733). A variety of antenna configurations, and beam transmitters was used (Bertha I, Bertha II), and a number of co-located transponder transmitters (S16B, Sadir 80/100).

An interesting beacon system is the Hermes/Hermine "Sprechdrehbake" system ("Talking Beacon"). The system was originally developed in response to a tactical requirement formulated during the second part of 1942, as a navigational aid for the purpose of giving an approximate bearing to single-engine night fighters engaged in "Wilde Sau" air-defence operations. The pilot could determine the bearing from the beacon, without having to look at an instrument. The beacons (FuSAn 726) transmitted voice-announcements of the beam azimuth in real-time, every 10º. I.e., the numbers 1 - 35 (multiples of 10º), and the "station call-sign" for 360º = 0º = north. The voice stream was pre-recorded as an optical track on a film strip ("Tonfilm"). The voice signal was transmitted with an omni-directional antenna. At the same time, and on the same frequency, a strong constant 1150 Hz tone was transmitted. However, it was transmitted with a rotating cardioid antenna pattern. The null of the pattern ( = no 1150 Hz interference signal) coincided with the momentary direction as announced by the voice announcement. The airborne counterpart, FuG125 "Hermine", comprised an EBl 3 receiver with increased audio bandwidth, an FBG2 control panel, and a small audio-amplifier (model V3a or ZV3). The system was developed in 1943/44 by Ernst Kramar of the Lorenz company.

Hermine

Fig. 48: Principle of the "Hermine" talking beacon system


In addition to the beacon systems described above, there was a number of other German beacon systems (ref. 1, 2, 26B, 33), such as:

  • Komet (FuSAn 712) / Komet-Bord (FuG 124), concentric rings of antennas for multiple operational HF frequencies (short wave); proved impossible to adjust/calibrate. Development and evaluation from 1941 through the end of the war.
  • Elektra: long wave; Kriegsmarine.
  • Dreh-Elektra.
  • Elektra kurz (1939-1941).
  • Sonne: long wave (several frequencies between 250 and 350 kHz), long-range system of the Kriegsmarine. It was based on "Elektra", but rather than rotating a loop antenna, Sonne used three stationary antennas spaced about 1 km (about 3 wavelengths) and a single transmitter, to electronically sweep the direction of the beams.
  • Goldweber: a "Sonne" derivative that never became operational,
  • Erich: VHF system
  • Erika: a VHF beacon, comprising a line of six antenna arrays (spaced ca. 46, 18, 27, 27, and 124 m) each with a transmitter. Similar to the British Gee system.
  • Dora: ca 1940, shortwave, 2 pairs of vertical dipoles in crossed configuration, with a vertical antenna at the center, rotating dual cardioid pattern; not satisfactory. 1.5 kW beacon, used for calibrating Erika.
  • Mond,
  • Baldur, VHF system
  • Drehbake "M", UHF system.

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

A. Hitler

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

H. Göring

Source: p. 53, 157 in ref. 5 (German edition).

PATENTS

Below is a listing of patents related to Bernhard/Bernhardine.

Patent number Patent office Year Inventor(s) Patent owner(s) Title (original) Title (translated)
577350 RP 1932 E. Kramar C. Lorenz A.G. Sendeanordnung zur Erzielung von Kurslinien Transmitter arrangement for producing course lines
662457 RP 1935 W. Runge
K. Röhrich
Telefunken GmbH Antenneanordung zur Aussendung von zwei oder mehreren einseitig gerichteten Strahlen Antenna arrangement for transmission of two or more uni-directional beams
737102 RP 1935 W. Runge Telefunken GmbH Anordnung zur ständigen Kontrolle und zur Ein- bzw. Nachregulierung der geometrischen Lage eines Leitstrahls während des Leitvorganges Arrangement for monitoring and adjustment of the location of a directional beam
767354 RP 1936 - Telefunken G. für drahtlose Telegraphie m.b.H. Verfahren zur Richtungsbestimmung Method for direction-finding [this is the primary "Bernhard" patent]
767512 RP 1938 - Telefunken GmbH Verfahren zur Richtungsbestimmung mittels rotierender Richtstrahlung Method for direction finding by means of a rotating directional beam
767513 RP 1939 A. Lohmann Telefunken GmbH Empfangsseitige Schreibvorrichtung zur Durchführung eines Verfahrens zur Richtungsbestimmung [Wachsschreiber] Receiver-side printer for the implementation of a method for direction-finding [wax printer, infinite loop, erasable tape]
767515 RP 1940 A. Lohmann Telefunken GmbH Anwendung des Registrierverfahrens nach Patent 767354 für ein Verfahren zur Führung eines Luftfahrzeuges während des Landungsvorganges Application of the printing method per Patent 767354 for a method for aircraft guidance during landing
767523 RP 1938 A. Lohmann
A. Bittighofer
Telefunken GmbH Empfangseinrichtung zur Durchführung des Verfahrens zur Richtungsbestimmung Receiver-side device for the implementation of the method for direction-finding
767524 RP 1938 A. Lohmann Telefunken GmbH Verfahren zur Richtungsbestimmung mittels rotierender Richtstrahlung Method for direction-finding with a rotating directional beam
767525 RP 1938 A. Lohmann Telefunken GmbH Einrichtung zur Speisung eines rotierenden Richtantennensystems Device for capacitive coupling of a transmitter to a rotating directional antenna system
767526  RP 1938 A. Lohmann Telefunken GmbH Verfahren zur Richtungsbestimmung Method for direction finding
767527 RP 1938 A. Lohmann Telefunken GmbH Einrichtung zur periodischen Ein- bzw. Ausschaltung einer Registriervorrichtung Device for switching on and off of a printer
767528 RP 1936 A. Lohmann Telefunken GmbH Verfahren zur Richtungsbestimmung Method for direction finding [optical disks, quadruple antenna]
767529 RP 1938 A. Lohmann
A. Bittighofer
Telefunken GmbH Einrichtung zur Erzeugung angenähert rechteckiger, zur Modulation des Kennzeichensenders dienender Abtastimpulse bei einem Verfahren zur Richtungsbestimmung mittels Drehfunkfeuer Device for the generation of an approximately square pulse envelopes, for the direction finding method by means of a rotating beacon
767530 RP 1938 A. Lohmann Telefunken GmbH Verfahren zur Richtungsbestimmung Method for direction-finding [frequency shift for beacon tone frequencies]
767531 RP 1939 A. Lohmann Telefunken GmbH Verfahren zur Richtungsbestimmung Method for direction-finding [dipole antenna array arrangement with side-lobe suppression]
767532 RP 1939 A. Lohmann Telefunken GmbH Sendeanordnung zur Durchführung eines Verfahrens zur Richtungsbestimmung Antenna arrangement for the implementation of a method for direction finding
767534 RP 1940 A. Lohmann Telefunken GmbH Verfahren zur Richtungsbestimmung Method for direction-finding
767536 RP 1940 A. Lohmann Telefunken GmbH Empfangsseitige Schreibvorrichtung zur Durchführung eines Verfahrens zur Richtungsbestimmung Receiver-side printer for the implementation of a method for direction-finding
767537 RP 1938 A. Lohmann Telefunken GmbH Anwendung des Peilverfahrens nach Patent 767354 für die Standortbestimmung Application of the direction finding method of patent 767354, for position finding [printing of two beacons for triangulation]
767538 RP 1939 A. Lohmann Telefunken GmbH Anwendung des Verfahrens nach Patent 767354 für die Standortbestimmung Application of the method of patent 767354, for position finding [receiver/printer arrangement for triangulation with two beacons]
767919 RP 1940 H. Muth Telefunken GmbH Verfahren zur Richtungsbestimmung unter Verwendung eines rotierenden Funkfeuers Method for direction-finding with a rotating beacon [using only twin-lobe beam]
767937 RP 1939 A. Lohmann Telefunken GmbH Einrichtung zur Durchführung eines Verfahrens zur Richtungsbestimmung Device for implementation of a process for direction finding [multi-track optical disk for quick change of identifier]
730635 RP 1937 R. Hell Dr.-Ing. Rudolf Hell Verfahren zur Registrierung des Verlaufes veränderlicher Stromkurven Method for printing the trace of varying signals [Hell printer for signal-level track of Bernhardine]

Here are some ancillary patents:

Patent number Patent office Year Inventor(s) Patent owner(s) Title (original) Title (translated)
562307 RP 1929 J. Robinson J. Robinson Funkpeilverfahren Method for direction finding [transmission of course-pointer, or compass rose info via Nipkow-video]
620828 RP 1933 - C. Lorenz AG Funkpeilverfahren Method for direction finding [transmission of compass rose info via Nipkow-video]

Patent office abbreviation: RP = Reichspatentamt (Patent Office of the Reich), DP = deutsches Patentamt (German Patent Office)
Patent source: DEPATISnet

UNKNOWN / UNCONFIRMED / UNCLEAR ASPECTS

  • Did the simplified system with only ±4° accuracy (single-trace printer system,  single transmitter, single antenna array) ever enter into service?
  • Details about the (never finished) Bernhard 30 m / Bernhaube (FuSAn 713) system (see p. 224 in ref. 2), operating on a frequency around 10 MHz (a wavelength of 30 m, which suggests larger antenna systems than for the 30 MHz / 10 m "Bernhard"). Apparently it used electronic beam steering instead of a rotating antenna system. Supposedly, the FuG 10 radio system was used in the aircraft, but that radio set had a maximum frequency of 6 MHz...


REFERENCES


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