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By August of 2019, this page had grown to about 175 photos and diagrams. It had become rather large (ca. 20 MB download size). This caused long download times for some users. I decided to split the page into two separate pages. This split should be fairly transparent to you. Please continue using the (unchanged) items lists above and update your bookmarks - if necessary.


©2004-2019 F. Dörenberg, unless stated otherwise. All rights reserved worldwide. No part of this publication may be used without permission from the author.


Latest page update: October-November 2019 (added ref. 253, 244A-K, added high-res version of ref.15).

Previous update: August 2019 (split into two pages, added ref. 243).

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COMMAND UPLINK FEATURE

The "Bernhard/Bernhardine" system is simply a "UKW-Richtstrahl-Drehfunkfeuer und Empfangszusatz mit Kommandoübertragung". That is, a rotating VHF directional beacon system, with command-uplink capability.

Obviously, the primary purpose of a beacon is to be a navigational aid. With a single beacon, only the relative bearing ( = direction) to/from that particular station can be determined (unless the beacon somehow allows the slant range ( = distance) between beacon and aircraft to be determined). I.e., only a position line ("Standlinie") from the beacon (with known location) can be determined, and neither distance 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").

Triangulation

Fig. 86: Determining bearing angle with a single beacon, and position via triangulation with two beacons

(the bearing angle is measured clockwise from North)

The "Bernhard" beacons were used by fighter aircraft that were engaged in intercepting inbound enemy aircraft, primarily bombers. It was the task of regional fighter control stations ("Jägerleitstellungen", "Jägerleitstände") to guide fighter aircraft to their target. The required guidance, instructions, and information was continuously provided via HF and VHF voice radio (radio telephony, R/T). A standardized short message format was used for the broadcast stream of the so-called "Running Commentary" ("Laufende Reportage"). This was used in German fighter control systems such as "Zahme Sau" ("Tame Boar") and "Wilde Sau" ("Wild Boar"). See §22-25 in ref. 6, ref. 25. In particular, later during WW2, with increasingly frequent Allied bombing raids on Germany, the fighter control voice frequencies became saturated. On top of that, the voice frequencies were also subject to Allied jamming. As a backup, the same short messages could be broadcast in spoken form via certain radio navigation beacons, and also via some Morse beacons (§59 in ref. 25).

The 1938 Telefunken patent 767512 already addressed using the "Bernhard" beacons to broadcast the relative direction for intercepting enemy aircraft. It proposes to transmit an extra heavy tick-mark in the compass scale, see Figure 86B. This could be used to indicate a target azimuth (the radial from the ground station) that is to be intercepted. The patent suggests implementation with a fixed notch (cam) on the edge of the encoder disk, and a contact that is adjustable to the desired target azimuth (Fig. 86A). The notch would actuate a switch that was simply connected in parallel with the output of the photocell of the optical disk. However, this target-azimuth marker method would not have been very practical: it could only be received by aircraft that are already flying on nearly the same bearing from the beacon station as that target. Also, the command/guidance would be limited to conveying a target azimuth.

Notched optical disk

Fig. 87A: Notched optical disk

(source: Figure 2 in patent 767512)

Tarfet azimuth bar

Fig. 87B: Target azimuth bar superimposed on azimuth data

(source: Figure 3 in patent 767512)

However, the "Bernhard" beacon already broadcasts information in textual form: the fixed numbers of the compass scale and the station identification letter. Why not use the same Hellschreiber system for transmitting short, programmable text messages? Excellent idea! But the beacon rotates, and the beam is only received during about 3+ to 5 sec out of every 30 sec rotation (depending on distance from the beacon). At 12°/sec rotation, about a 40-60 degree section of the compass scale is printed each time. Clearly, it must be guaranteed that the complete message is printed during a single beam passage, independent of the bearing from the station on which the aircraft is flying within the operating range of the system. This limits the number of text characters that can be put into a single message.

Let's assume that transmission of the message is continuously repeated as the beacon rotates. To always guarantee that a complete message is received, not one, but two back-to-back copies of the message must fit within a single beam passage! If not, the end of one message is printed, immediately followed by the beginning of the next copy of the same message. This by itself is bad enough, but it is also not possible to determine if all characters of the message have been received. This factor of two further limits the number of text characters that can be put into a single message...

Figures 76B and 76C above show that a traditional Hellschreiber font with five pixel-columns per character is used for the compass scale. Also as standard for Hellschreiber fonts, each character has a leading and a trailing pixel-column that is blank. This is for character spacing. The compass scale has three pixel-columns per degree. Each character spans 5 + 2 = 7 pixel-columns. Hence, at least about 20 characters can be received per beam passage (also per item 9 on p. 10 ( = Blatt 11) of ref. 198A). Therefore, the length of one complete message is limited to about 20 / 2 = 10 characters. To mark the beginning of each message, a delimiter symbol must be used. The start-delimiter of the next message-copy automatically marks the end of the preceding one, which allows confirmation that a complete message has been received. This leaves up to 9 characters of actual fighter guidance information. The messages had the same content about an inbound enemy bomber formation as the "Running Commentary" guidance and instructions, but captured as simple coded groups of letters and numbers. The following format was used (p. 275 in ref. 5B):

  • The "+" symbol as a message-start delimiter.
  • Altitude (in 100s of meters) of the lead-aircraft of the enemy bomber formation.
  • A two-digit identifier of the specific box of the "Jägergitter" (a.k.a. "Jägernetz") air defense grid,in which the enemy lead-aircraft is currently located (e.g., "QR" for the box around the city of Mainz).
  • The two-digit course of the bomber group (in 10s of degrees).
  • Size of the group (estimated number of aircraft).

Karte

Fig. 87C: grid-box "QR" near the city of Mainz

(source: ref. 244G)

In some literature, allied bomber formations are generically referred to as "bomber streams" (in Luftwaffe terminology: "Bomberströme"). However, that term only refers to a specific form of sequencing (night) bombers, used by the RAF from the end of May 1942 until the end of the war. The purpose of this tactic was to create a string of bombers (with designated altitude bands and time slots), that would pass through the narrow German (night) air defense system via a minimum number of "boxes". This defense system, established in 1940 by then-colonel Josef Kammhuber, comprised a chain of rectangular "Himmelbett" airspace control zone "boxes". The chain eventually reached from Denmark to the north of France, and was referred to by the British as the "Kammhuber Line". Ref. 5, 27. The zones had search and tracking radars (first Freya and Würzburg radar systems, later also Würzburg Riese) and groups of search lights (some radar controlled). Funneling all bombers through one or a few boxes, quickly overloaded the German defense capability of the boxes. Each box was covered by a single night fighter (with one backup fighter), that could make an estimated 6 intercepts per hour at best.

Depending on the message content, 8-10 message characters were sent (including the delimiter). The following hand-drawn figure from 1945 illustrates the message "+40KA27100". Unfortunately, it not only (incorrectly) suggests that the station identifier was sent every 20° instead of every 10°, but also (incorrectly) suggests that the messages were sent in addition to the compass scale (ref. 5A actually states so). Note that these command messages were transmitted instead of the compass scale, as there was simply no third printer-track.

Bernhard reportage track

Fig. 88: Misleading of rendition a "Bernhardine" print-out with Reportage track at the bottom

(source: ref. 6 (1945), very similar image in ref. 5A)

In the compass scale format, there is one tick-mark for every degree. These tick-marks are also used to synchronize the compass scale Hell-printer to the Hell-format transmission (as explained in the "Optical Encoder Disk" section). As the same printer channel is used for the command messages, it must now also be synchronized to the command message transmission. This requires tick-marks. Here, a tick-mark is implemented at the top of every single pixel-column, instead of every third column (p. 4 ( = Blatt 3) of ref. 198A). Retaining the tick-mark at the top of every third pixel-column could only have worked with a Hell-character font that is 6 pixel-columns wide (incl. blank columns for character spacing). With a tick-mark at the start of each pixel-column, there is no such limitation. Also, having more sync tick-marks than once per degree does not upset the sync mechanism: the synchronization electro-magnet of the compass scale printer-channel is activated by all black pixels, whether tick-mark or other part of the transmitted symbology.

The upper track of the "Bernhardine" printer is used to plot the signal-strength curve. The curve has a sharp V-shaped dip in the middle, which is used as a pointer for the compass scale that is normally printed below it. Clearly, the pointer-curve is not used in combination with the command messages. However, the signal-strength printer channel is not turned off, as it is linked to the automatic motor start/stop function.

The next figure illustrates what a real print-out with a command message would have looked like:

Bernhard reportage track

Fig. 89: re-created Bernhardine print-out with command-uplink message


As stated above, the "Reportage" messages were sent instead of the compass scale data from the optical encoder disk. So, somewhere, these messages were converted from a text-string input to a Hellschreiber pixel stream. This could have been done with a keyboard and tape-puncher, combined with a "punch tape to Hellschreiber pulse-sequence converter". This was the normal way with the "Presse Hellschreiber" system. The tape could be looped through the tape reader to repeat the message. Of course, speed and text font would have had to be adapted. However, p. 87 in ref. 2 and p. 392 in ref. 7B suggest that a different method was used to program the text character sequence: inserting jumpers ("Stöpsel") into a patch-board ("Stecktafel"). Mid-2015, I finally obtained confirmation of this, by the photo shown below (ref. 93A). It was taken inside the cabin below the rotating superstructure of the Bernhard installation Be-10 at Hundborg/Denmark. The photo shows two transmitter-modulators, two monitor Hellschreiber printers (printing signals from a nearby remote monitoring receiver and antenna), and a patch-board with patch cords. There are 9 jacks for each of up to 9 selectable characters. With some difficulty, one can see that the left-hand column is labeled A-Z, and the right-hand column 1-9, 0, +, ... So, the conversion from text strings to Hellschreiber pixel streams was done at the Bernhard station, based on telephone or teleprinter messages from the regional fighter command & control center.

Reportage - Kontrollpult

Fig. 90: Lower left-hand corner - patch-board & patch-cords for selecting command-message text string

(source: Figure 30 in ref. 93A; photo taken at Be-10 Hundborg/Denmark)

The actual patch-board and patch-cords appear to be very similar to what was used during the 1930s in standard small German telephone switchboards:

Reportage - Kontrollpult

Fig. 91: Left "Klappenschrank" telephone swithboard model OB-14; right: 50-line Wehrmacht PBX

(source OB-14: Fernmeldemuseum Dresden; "OB" in "OB-14" stands for "Ortsbatterie", meaning local battery operation)

This patch-board method is similar to what was used in the mechanical Siemens-Hellschreiber-sender model 44 in the 1960s. This sender has a character-drum with 19 notched disks and associated slip-contacts: seven disks to generate the pixel sequence for the characters A - G, ten for the figures 0 - 9, and one notched disk for the character "-". This machine sent a string of eight characters, based on a discrete code at its inputs (representing status and self-test results from a telephone exchange system).

Reportage - Kontrollpult

Fig. 92: The inside of a Siemens-Hell model 44E with a stack of notched character-generator disks at the center


A similar method with a stack of notched disks may have been used for generating Bernhard message strings in Hellschreiber format. When the messages had to be sent, the output of the photocell of the optical azimuth disk was simply disconnected, and the pixel stream of the text message generator was used instead.

Note that the command-uplink capability was not a standard feature of the "Bernhard" stations. 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 (including station Be-10 at Hundborg in Denmark).

Apparently, late 1943 / early 1944, the Lorenz company also experimented with an expanded Hellschreiber-based command data-link system, referred to as "Sägezahn" ("sawtooth", ref. 26A).

The Bernhard/Bernhardine system was the first and only operational ground-to-air data-link system of the second World War that had freely formattable messages! Since about the year 2000, the same concept has been introduced to "modern" civil aviation: Controller-Pilot Data Link Communications (CPDLC); since 2015 its usage is mandatory in European airspace above 28500 ft. CPDLC is for up-linking routine ( = non-time-critical) air traffic control instructions and clearances to aircraft via digital radio. Purpose: reduce the significant time that air traffic controllers spend on routine communications over VHF voice links, and help reduce miscommunications as well as "stuck microphone" issues (which block the radio channel). However, contrary to the Bernhard system, the pilot can now respond to messages, request clearances and information, and declare an emergency.

The official German Bernhard/Bernhardine system description documents (ref. 181, 183, Blatt 8 & 10 in 198A) clearly state that the Bernhard-beacon rotated once every 30 sec, i.e., at 2 rpm. The specified diameter of the center of the circular rail track ( = midway between the two rails) was 2x10.55 = 21.1 m (ref. 193). Hence, the track length was 66.28 m. This means that at 2 rpm = 120 rph, the small locomotives that turned this enormous antenna installation, moved at a respectable speed of 8 km per hour (5 mph). As described in the "Locomotive system" section below, the rotational speed of the system was determined by a single synchronous 3-phase AC motor in one of the four locomotives. The 3-phase AC power was provided by a DC-AC inverter that had a fixed reference frequency. Hence this motor could only turn at the reference speed, and the speed was monitored very accurately. The rotational speed of the beacon was kept constant to within -0.2 to +0.3% ! See p. 80 in ref. 181 and p. 8 & 18 in ref. 183.

The official German system descriptions and the manual of the FuG 120 "Bernhardine" printer system also state the same 2 rpm speed (top of Section B on p. 5 in ref. 15, sheet 8 & 10 of ref. 198A). Moreover, the "Bernhardine" printers were simply not compatible with antenna rotational speeds that deviated more than a couple of percent from that nominal speed! As with other types of synchronized teleprinter systems, the motor of the Bernhardine-printer had to turn 1-2% faster than nominal system speed (p. 18 in ref. 183).

There are some persistent statements that the "Bernhard" beacons rotated with a period other than 30 sec. Some of the sources for these statements are the following:

  • The French resistance explicitly reported in 1943 that this station Be-3 at Le-Bois-Julien rotated once per minute (p. 62 in ref. 91).
  • A British 10 cm [ = 300 MHz] radar station at Fairlight (on the East Sussex coast, east of Hastings, 87 km [54 miles] northwest of Be-3 at Le-Bois-Julien) concluded that the station appeared to rotate once a minute (ref. 173B, December 1943). Likewise, extensive radar measurements early-June 1944 also concluded that the rotation period was 52-60 sec (ref. 173A).
  • Luftwaffe POWs in the UK reported 1 rpm for the Bernhard system in general (§10, 18, 19 in ref. 6)
  • A 1946 US air force survey of German electronics development, stating that "... information is printed once per minute" (ref. 93B). This may have been based on war-time "intelligence" from other sources.
  • A "reliable informant" who saw the Marlemont station, reported to the British that he was told [correctly] that it rotated with a speed of 8 km/h. Based on the wrong British photometric assumption that the Bernhard-ring had a diameter of 82 ft [25 m], a rotational period of 36 sec. was estimated. Ref. 173E. For the actual diameter of 71 ft [21.5 m], the correct period of 30 sec. would have been obtained.

The 1936 Lohmann/Telefunken patent 767528 states that the limiting factors for the upper limit of the antenna's rotational speed, are the printing speed of the Hellschreiber and the required pixel resolution of the printed information. Given the large size and weight of the antenna system, there are obviously also mechanical considerations for the upper speed limit. The patent proposes to resolve this, by quadrupling the number of antenna beams, spaced at 90º intervals. Each optical encoder disk would simply have four "light source plus photocell" pairs (two pairs shown in the diagram above), that could be adjusted to account for angular offsets between the beam centerlines.




REMOTE MONITORING-ANTENNA MAST & RECEIVER

The signals transmitted by the "Bernhard" beacon were monitored via a remote receiver and antenna. They were located at a nominal distance of 500 m (p. 21 in ref. 183; 400 m per ref. 13) from the beacon. The far-field of the transmitting antennas started about two wavelengths from those antennas, i.e., at about 20 m. So, why locate the monitoring antenna and receiver so far away? Most likely because the Mercury Arc Rectifier of the locomotive drive system caused a lot of radio interference near the beacon, and because the null of the twin-beam radiation pattern was not sharp enough close to the beacon. The latter was very important, in particular during calibration of the antenna radiation pattern. The 1935 Telefunken/Runge/Krügel/Grammelsdorff patent nr. 737102 proposes using a fixed-location remote receiver to check the direction of the beam-null, as measuring and balancing antenna feed-currents does not guarantee its correctness.

The vertical antenna was installed on top of a steel truss mast (lattice mast, cage mast; D: "Eisengittermast"). The antenna has a pointed tip, just like the feedpoint of the dipoles of the Bernhard's antenna arrays. A ladder was integrated into the mast. It consists simply of horizontal sections of L-bracket, mounted between one of the mast legs, and the braces to one of the adjacent mast legs. The box on which the antenna radiator is mounted, is about 50 cm wide. The monitoring receiver was located at the base of the antenna (p. 21 (pdf p. 18) in ref. 183, sheet 8 in ref. 189). The received signals were printed with a "Bernhardine" Hellschreiber-printer in the equipment room below the beacon's rotating superstructure (see Figure 143 above).

Berhard station

Fig. 93: The monitoring antenna mast of Be-11 at Trzebnica/Trebnitz

(photo (1980s): courtesy C. Piotrowski, used with permission)

This "Kontrollmast" (monitoring mast) had a height of 20 m (≈66 ft; p. 21 in ref. 183). According to US photographic intelligence (ref. 13), the mast was about 30 m (≈100 ft) tall, and the vertical antenna (hollow pipe) on top of it about 2.4 m (8 ft). Photometric analysis of the photo above shows that the antenna radiator (on top of the box at the top of the mast) is about 2.6 m tall, assuming a 20 m tall mast. I.e., it was a standard 1/4 wavelength vertical antenna. It has a pointed tip, just like the feedpoints of the vertical dipoles of the "Bernhard" antenna arrays, so possibly it was just half of such a dipole leg. The mast was installed on a concrete foundation.

So far, I have been able to determine the location of the monitoring antenna of the following Bernhard stations:


The mast and antenna were built by Hein, Lehmann & Co., the same company that built and installed the dipole antenna arrays of the Bernhard systems for Telefunken. The tall mast was delivered pre-assembled to the "Bernhard" site - at least at Aidlingen/Venusberg (ref. 103). Telefunken placed an order for six such masts in 1941, at a price of 2020 Reichsmark (RM) each (ref. 177C). This is equivalent to roughly US$12500 and €11500 end-2016, based on general inflation data (ref. 178A-178C). Note that Consumer Price Index (CPI) inflation data does not necessarily apply to specific products (such as antenna masts, electronics) or services. The billing does not state if the price included the actual antenna rod.

The photo below shows the mast of Be-11 at Trebnica/Trebnitz in Poland. It is the only "Bernhard" mast that has survived to date (2014). It is being used for antennas of a local FM radio station. The officially registered height of this "object" is 22 m (ref. 129).

Berhard station

Fig 94 Looking up inside the monitoring antenna mast, and the base of the mast at Be-11 Trzebnica/Trebnitz

(©2014 C. Piotrowski, used with permission)

Berhard station

Fig. 95: The dimensions of the standard concrete foundation of the monitoring masts

(data source: Czarek Piotrowski, used with permission)

Each mast was placed on a 3x3 meter concrete slab foundation. The concrete slab is at least 75 cm thick (2½ ft). The one shown below on the left, has two oblong dimples (see arrows). They measure 19x17 cm and 21x21 cm, respectively. Their purpose is unknown. Possibly they are vertical holes in the concrete, for inserting steel posts for mounting equipment, such as shown in Fig. 97 below. Possibly, those posts were embedded in the concrete, and the photo shows the cutt off remnants.

Berhard station

Fig. 96: Concrete foundations of the monitoring mast of Be-9 at Bredstedt (left) and Be-10 at Hundborg

(sources: R. Grzywatz (Be-9); Hundborg Lokalhistoriske Arkiv (Be-10); both used with permission)

The monitoring receiver was located at the bottom of the mast (D: "Empfänger am Fuß des Masts"; p. 21 (pdf p. 18) in ref. 183, sheet 8 in ref. 189):

Berhard station

Fig. 97: Monitoring mast - remote-receiver and cable installed at the bottom of the mast

(source: ref. 13; probably Be-4 at La Pernelle,, based on the other photos in ref. 13)

Figure 163 above shows two equipment boxes installed near the bottom of the mast. Field line installations often had lightning protection at both ends: fuses (D: "Blitzschutzpatronen") in a junction box ("Anschlußkasten", AK). This may account for the second box.

The receiver was remote-tuned from the "Bernhard" station (D: "fernbedienter Empfänger"; p. 21 (pdf p. 18) in ref. 183, sheet 8 in ref. 189). Each "Bernhard" beacon used one of 32 operating channels in the 30-33.3 MHz frequency band. To be able to use the same monitoring receiver at all Be-stations, it had to be tunable. Another reason remote-tuning is that the transmitting frequency could be changed for technical or tactical reasons. It took 1-2 minutes to change the receiver frequency to a new channel frequency (p. 27 (pdf p. 24) in ref. 183).

There was an underground cable between the receiver and the Hellschreiber printers & control equipment in the round room below the rotating superstructure of the beacon. The cable was of type "Erdkabel RLM", special in-ground cable with a very robust outer insulation ("Kabelmantel"). It had four conductors with a 1 mm2 diameter (line item 28a on sheet 8 in ref. 189; ≈AWG #18). The receiver audio was also fed to a monitoring loudspeaker in the guard office near the beacon (line item 29a on sheet 8 in ref. 189).

So, what kind of remotely tunable receiver was used? The aircraft that used the "Bernhard" beacons had an EBL-3 receiver on board. The "F" version of this receiver had remote-control. However, the control interface by itself already required 4 wires just for tuning (p. 87 and Fig. 17 in ref. 72). Note that the antenna mast is also referred to as a "Diodenmast" (e.g., ref. 99). This German term suggest that a "Diodenempfänger" was used (a.k.a. "Detektorempfänger", "Kristalldetektorempfänger"). This is known in English as a "crystal radio" or "crystal set". They were popular in the early days of radio, and got their name from a small piece of crystal that was used in the signal detector. In the 1930s, the inconvenient "crystal detector" was replaced with a diode. Such diode-receivers are not only simple, they are also passive. No separate source of electric power, such as a battery or DC voltage via a cable, is required: the simple circuit is powered by the received radio signals. Also, it is very easy to remote-tune a crystal radio: all that is needed is a small low-rpm DC motor that rotates the shaft of the tuning capacitor (esp. a capacitor without angular limitation). Four conductors would have sufficed for audio (2 wires) and DC power (2 wires, possibly with reversible polarity to change tuning direction).

Would the audio output of a diode-receiver have been strong enough, without active amplification? This depends on three parameters:

  • The signal level required at the input of the Hellschreiber printer-amplifier in the cabin. A Wehrmacht Hell Feldfernschreiber had a specified nominal output signal amplitude of 2.5 volt (900 Hz tone pulses). To ensure proper printing at a receiving Feld-Hell machine, the maximum allowed cable damping was 5 Neper, which is about 43 dB, or a voltage attenuation factor of about 140x. That is, the printer amplifier required an audio input signal with a minimum amplitude of 2500 / 140 ≈ 18 mV.
  • The signal attenuation (damping) of the audio signals over field telephone cable with a length of 1 km (the maximum distance between the mast and the "Bernhard" ring). According to a 1945 manual of the Hell Feldfernschreiber (ref. 146), its range over standard field telephone cable of type DL500 was 36 km (22 km when wet), 60 km over regular pupin-cables (D: "bespultes Kabel", "Pupin-Kabel"; cable with a loading coil/inductance at regular intervals, typ. 250 m for German field cable), and 160 km over special pupin-cable of type FL250. That is, worst-case 22 km for 43 dB damping, or no more than 2 dB for 1 km. The required minimum 18 mV plus 2 dB is about 23 mV. So that would have been the required minimum output signal of the diode-receiver.
  • The RF field-strength induced at the remote antenna by the "Bernhard" transmitters and antenna system. Per the definition of the ITU (ITU-R BS.561-2), the field strength of a ½λ-dipole with an effective radiated power (ERP) of 1 kW is 222 mV per meter, at a distance of 1 km. Also see ref. 150. The "Bernhard" installation had an ERP of at least several kW (my estimate). I.e., at least several 100 mV per meter at the monitoring antenna. That would have been more than enough to generate 23 mV at the receiver output!

The schematic below shows a crystal radio that can power a small loudspeaker (ref. 147), similar to a small 1-transistor radio. It has a double-tuned circuit, a full-wave diode rectifier, followed by a voltage-doubler. The output voltage across the capacitors can be connected directly to standard high-impedance headphones (4000 Ω). It can also be connected to a low-impedance load, such as a loudspeaker or a standard "600 Ω" phone line. To match that impedance, a simple output-transformer (about 1:6 to 1:10) must be used. Solid-state diodes were readily available at the time, such as "Sirutor" diodes that were used in various Hellschreiber models. These were quite suitable for crystal radios (ref. 148, 149), as they have a forward voltage (a.k.a. "knee" or "turn-on" voltage) of only 0.2-0.3 volt (Sirutor type 1b).

Berhard station

Fig. 98: Schematic of a "crystal radio" receiver, capable of driving a small loudspeaker

(source: adapted from ref. 147)

Berhard station

Fig. 99: A "crystal radio" receiver built per the schematic above

(source: ref. 147)




ROTATIONAL SPEED

The official German Bernhard/Bernhardine system description documents (ref. 181, 183, Blatt 8 & 10 in 198A) clearly state that the Bernhard-beacon rotated once every 30 sec, i.e., at 2 rpm. The specified diameter of the center of the circular rail track ( = midway between the two rails) was 2x10.55 = 21.1 m (ref. 193). Hence, the track length was 66.28 m. This means that at 2 rpm = 120 rph, the small locomotives that turned this enormous antenna installation, moved at a respectable speed of 8 km per hour (5 mph). As described in the "Locomotive system" section below, the rotational speed of the system was determined by a single synchronous 3-phase AC motor in one of the four locomotives. The 3-phase AC power was provided by a DC-AC inverter that had a fixed reference frequency. Hence this motor could only turn at the reference speed, and the speed was monitored very accurately. The rotational speed of the beacon was kept constant to within -0.2 to +0.3% ! See p. 80 in ref. 181 and p. 8 & 18 in ref. 183.

The official German system descriptions and the manual of the FuG 120 "Bernhardine" printer system also state the same 2 rpm speed (top of Section B on p. 5 in ref. 15, sheet 8 & 10 of ref. 198A). Moreover, the "Bernhardine" printers were simply not compatible with antenna rotational speeds that deviated more than a couple of percent from that nominal speed! As with other types of synchronized teleprinter systems, the motor of the Bernhardine-printer had to turn 1-2% faster than nominal system speed (p. 18 in ref. 183).

There are some persistent statements (e.g., ref. 5A) that the "Bernhard" beacons rotated with a period other than 30 sec. Some of the sources for these statements are the following:

  • The French resistance explicitly reported in 1943 that this station Be-3 at Le-Bois-Julien rotated once per minute (p. 62 in ref. 91).
  • A British 10 cm [ = 300 MHz] radar station at Fairlight (on the East Sussex coast, east of Hastings, 87 km [54 miles] northwest of Be-3 at Le-Bois-Julien) concluded that the station appeared to rotate once a minute (ref. 173B, December 1943). Likewise, extensive radar measurements early-June 1944 also concluded that the rotation period was 52-60 sec (ref. 173A).
  • Luftwaffe POWs in the UK reported 1 rpm for the Bernhard system in general (§10, 18, 19 in ref. 6)
  • A 1946 US air force survey of German electronics development, stating that "... information is printed once per minute" (ref. 93B). This may have been based on war-time "intelligence" from other sources.
  • A "reliable informant" who saw the Marlemont station, reported to the British that he was told [correctly] that it rotated with a speed of 8 km/h. Based on the wrong British photometric assumption that the Bernhard-ring had a diameter of 82 ft [25 m], a rotational period of 36 sec. was estimated. Ref. 173E. For the actual diameter of 71 ft [21.5 m], the correct period of 30 sec. would have been obtained.

The 1936 Lohmann/Telefunken patent 767528 states that the limiting factors for the upper limit of the antenna's rotational speed, are the printing speed of the Hellschreiber and the required pixel resolution of the printed information. Given the large size and weight of the antenna system, there are obviously also mechanical considerations for the upper speed limit. The patent proposes to resolve this, by quadrupling the number of antenna beams, spaced at 90º intervals. Each optical encoder disk would simply have four "light source plus photocell" pairs (two pairs shown in the diagram above), that could be adjusted to account for angular offsets between the beam centerlines.



THE CABIN

Below the antenna installation, and rotating with it, is a steel truss bridge. The rectangular bottom frame of the bridge is made of heavy I-beams. It is supported by the four locomotives and by the round building at the center of the concrete ring. The upper frame of the bridge was suspended from the large lattice truss-joist of the lower antenna system.


Bernhard

Figure 100: Cabin of Be-4 at La Pernelle/France


Inside the bridge is a long wooden cabin ("mitdrehendes Holzhaus"). It measured about 20x4x3m (LxWxH, ≈66x13x10 ft), based on p. 20 in ref. 183, as confirmed by photometric analysis of available photos. Its length is close to the inside diameter of the ring (≈20.5 m). The cabin was made of heavy wooden planks. There is a entrance door and set of stairs at both ends of the cabin.

Ca. 1943, Telefunken contracted its standard antenna structure supplier, Hein, Lehmann & Co., to provide "Panzerung von Holzhäusern" for 12 "Bernhard" stations (purchase order nr. 253/33163, ref. 177C). That is, for sheet-metal protection of the wooden cabin. "Panzerholz" is plywood that is covered with sheet metal armoring on one side or on both sides. The price was 4167 Reichsmark per BE-station. Based on general inflation data, this is equivalent to ca. US$21,900 or €20,250 (early 2017, ref. 177). The metal protection was only installed at five stations (Be-2, Be-3, Be-4, Be-8, and Be-10), before the course of the war intervened. The protective panels probably took the form of large panels that could be slid in front of the cabin windows, see Fig. 91 below. The wooden part of the panels involved Fa. Rostock in Trebbin (ref. 176A). This company operated three owned or leased sawmills in Trebbin (close to Be-0) since the early 1930s, and supplied wooden construction materials for a number of "radar" installations and other Wehrmacht constructions.


Bernhard

Fig. 101: The cabin at Be-10 Hundborg/Denmark - with protective siding panels


At some "Bernhard" sites, these sliding covers are on the outside of the bridge frame that suspends the cabin from the truss-joist. At other sites, these panels slide between the cabin and that frame.

The cabin contained the two transmitters, AC/DC electrical power distribution and controls for the locomotive motors, and for cabin heating & lighting. See the "Electrical & signal distribution" section. Ref. 13 (p. 4.09) suggests that the cabin was divided into three sections. The section on the right (looking at the front of the antenna system) contained the transmitter equipment. This is confirmed by the layout diagram of the Be-0 station. The center section housed the controls for the four electric locomotives. The section on the left was a workspace. A plaque at La Pernelle (Be-4) states that it had one or more beds in it.

The photo below shows the power distribution and control panel ("Schaltwandtafel") inside the rotating cabin of Be-10 at Hundborg. The spoked handwheel in the lower right-hand corner (sheet 15/20 in ref. 189) belongs to the circuitry for bringing the locomotives up to speed from standstill, and for slowing down to standstill ("Kontroller und Anlaßwiderstand"). Also see the "Electrical & signal distribution" section.

Berhard station

Fig. 102: German engineer describing controls in the cabin of Be-10 at Bredstedt to a member of the RAF-ADW

(source: Australian War Memorial photo SUK14636, public domain; ca. August 1945)


THE FOUR CORNER-BLOCKS

At each of the four corners of the cabin, there is a "block" or square silo of about 1½x1½x2 m (WxDxH; ≈5x5x6½ ft). They are mounted on a cantilever, away form the main cabin and above the rear bogie of the locomotive underneath. There are no openings for ventilation in the walls or the roof. No conduits appear to emanate from the bottom. From the available photos it is clear that there are no windows, and it appears that there is no door. Whatever was in there, apparently did not require access! So it was not electrical or mechanical equipment, nor a container with brake sand for the locomotives (for which there would have been a tube descending in front of the powered wheels).

Bernhard

Fig. 103: One of the cantilevered corner sheds at La Pernelle

(source: 1946 film clip Cinémathèque de Normandie)

The next photo shows that the blocks were empty at some point in time:

Bernhard

Figure 104: Low-altitude oblique RAF aerial photo of the La Pernelle site

(source: ref. 172A; photo by G.R. Crankenthorp, taken on 3 March 1943)

Most likely, they contained dead weight (e.g., stone, sand, concrete, lead), to get more weight on the traction wheels of the locomotives - even though the entire structure carried by the locomotives was already quite heavy by itself. However, the blocks must have had considerable weight: a triangular stabilizing arm was installed between the cantilever supporting each block, and the bottom frame of the bridge:

Bernhard

Figure 105: One of the four stabilizing arms of the turntable at Be-10 in Hundborg


At some sites, these blocks have a flat roof (e.g., Be-9 at Bredstedt, Be-10 at Hundborg). At other sites, the four-sided roof is pointed (e.g., Be-4 at La Pernelle, Be-7 at Arcachon).

Bernhard

Figure 106: Corner-sheds with a flat roof (Be-10 at Hundborg/Denmark)


Bernhard

Figure 107: Corner-sheds with a pointed roof (Be-4 at La Pernelle/France)


Unlike the main cabin, the walls are not made of wooden planks - they apear to have been made of sheet metal:

Bernhard

Figure 108: Corner-block of Be-9 at Bredsted/Germany - note the construction details

(unedited photo taken May 1945 by Flt. Lt. Herbert Bennet, RAF Mobile Signals Units of No. 72 Signals Wing; © David Bennet; used with permission)

In available post-war photos of "Bernhard" installations (La Pernelle, Arcachon), the main cabin is completely stripped of its materials - but not the four corner-blocks! Either the material was hard to remove and carry away, not valuable enough, or not usable for some other reason.


Bernhard

Fig. 109: Post-war photo of Be-7 at Arcachon - installation dismantled and stripped, except for the corner sheds


Bernhard

Fig. 110: Post-war photo of Be-4 at La Pernelle - installation dismantled and stripped, except for the corner sheds


The photo below (a post-war postcard) of Be-2 at Mont-St.-Michel-de-Brasparts. The installation was dismantled in 1946, but the corner blocks were abandoned inside the concrete ring:

Berhard station

Fig. 111: Postcard of the Bernhard site at Mont-Saint-Michel-de-Brasparts (late 1940s / early 1950s?)

(source unknown)

No such blocks have been found at "Bernhard" sites were there still are visible remains these days.


THE LOCOMOTIVE SYSTEM

The superstructure of the "Bernhard" (i.e., the antenna system and bridge with cabin) was rotated by four electrically powered locomotives on the circular rail track. Each locomotive had two bogies (US: trucks). The photos below shows that each bogie had two axle-boxes with leaf-spring suspension. Such axle-boxes typically have greased sliding bearings (a.k.a., journal bearings, not ball bearings). Each of the locomotives had 2 x (2+2) = 8 wheels, so the four locomotives had 32 wheels in total. The weight of the superstructure was carried by the four locomotives and the round central support building below it. Let's assume that the weight was evenly distributed. So, the combined locomotives carried 4/5 x 120 = 96 metric tons. Hence, each wheel carried a weight of 96 / 32 = 3 metric tons. This is well below the standard railway limit of at least 11 tons/wheel, for the load at which both the rail head and full-size train wheels are damaged (about 6 tons/wheel for standard tramway ("Sraßenbahn") wheels).


Berhard station

Fig. 112: Each locomotive has two bogies (Be-10 at Hundborg) - 32 wheels in total

(source: www.gyges.dk, used with permission)


Based on photometric analysis, the locomotives measured about 4x1.2 m (LxH, 13x4 ft). The wheels on the outside rail had a diameter of about 60 cm (24 inch), the ones on the inside rail about 55 cm (22 inch). This is based on the diameters of the inside and outside rails being about 4.3% different, and the wheels on the inside rail having a diameter that is 2 x 2.4 = 4.8 cm smaller than the wheels on the outside rail. The wheels have about half the size of a standard rail wagon wheel, which is about the size of a tramway wheel.

Berhard station

Fig. 113: The side of the locomotive on the outside of the track - direction of motion is to the left


The next photos show that the locomotives had a large round access hole at both ends, normally covered with a rectangular cover plate. The right-hand photo shows that at least one of the locomotives had external down-gearing between a motor and the forward bogie. The down-gearing ratio is small: about 1.6:1. The gearing is covered, so it is not known if it was a belt or a chain.

Berhard station

Fig. 114: Close-up of a locomotives and external gearing of one of the locomotives (right)

(source: 1946 film clip of Be-4 at La Pernelle, Cinémathèque de Normandie)

As explained further below, each locomotive was driven by two motors. It is unclear if both bogies of each locomotive were driven, or only the forward bogie. It is also unclear if both axles of each driven bogie were driven, or only one per bogie. Dividing motor power evenly between multiple axles optimizes the use of the available traction, but complicates the construction. However, we know that each locomotive had two motors: either two DC motors (locomotives 1-3) or one DC motor and one synchronous AC motor (locomotive 4). Hence, most likely, each bogie had one motor.

The photos in Fig. 114 and 115 show that the locomotives supported the weight of the superstructure at the point halfway between the front and rear bogies - which makes sense. There was ball socket ("Kugelpfanne") at this point on top of the locomotive (p. 8 in ref. 193). The socket held a large downward-pointing ball-stud ("Kugelzapfen") that was mounted underneath the I-beam frame of the superstructure. Between the superstructure and the locomotives, there are only conduits for electrical power cables to the motors (and a tachometer signal, but only at locomotive nr. 4, see Fig. 116).

Berhard station

Fig. 115: Ball joint on a locomotive of Be-12 at Nevid and electrical conduits to the motors (magenta circle)

(source: brdy.org)

There were three motor types used in the locomotives (ref. 190):

  • "Hauptantrieb": main drive DC-motor. Only locomotives nr. 1-3 had such a motor.
  • Per ref. 189, the specified gauge of the wiring to each of the motors was 25 mm2 (≈ 5.6 mm Ø, equivalent to about AWG 3). The gauge between the control panel and the variable starter resistance was 95 mm2. I.e., a diameter of 11 mm (AWG 3/0-4/0). Note that aluminum wiring was specified for all cables. Aluminium has 61% of the conductivity of copper.
  • Input fuses were rated 160 A / 500 V.
  • "Nebenantrieb": auxiliary drive DC-motor, with a separately controlled field winding ("separately excited DC-motor"). All four locomotives had such a motor.
  • Per ref. 189, the specified gauge of the wiring to each motor's field winding was 2.5 mm2 (≈ 1.8 mm Ø, ≈ AWG 13), and 6 mm2 (≈ 2.8 mm Ø, ≈ AWG 9-10) to each armature winding.
  • The two input fuses were rated 35 A / 500 V.
  • "Synchronantrieb": 3-phase AC synchronous motor drive. The frequency of the AC power was accurately regulated. I.e., it was not taken from the variable 50 Hz public power grid or a local generator. Only locomotive nr. 4 had such a motor.
  • The wire gauge for the 3-phase AC was 16 mm2 (≈ 4.5 mm Ø, equivalent to AWG 5). Modern 4-conductor insulated aluminium cable of this gauge (e.g., cable type NAYY-J) has a current rating of 50 amps. The wiring for the DC field excitation was 2.5 mm2 (≈ 1.8 mm Ø, ≈ AWG 13). Modern 2-conductor cable of this gauge has a current rating of about 18 amps.
  • Associated fuses were rated 80 A / 500 V and 6 A / 500 V respectively.

Bernhard wiring

Fig. 116: Motorization of the four locomotives

(source: derived from ref. 189, 190)

That is, each locomotive had two motors! The DC motors provided gradual acceleration from standstill, the majority of the drive power that was required during normal operation, and regulation of the speed to within the speed-capture range of the single synchronous 3-phase AC motor in locomotive nr. 4. As explained further below, the latter motor provided the required highly accurate speed control.


LOCOMOTIVE POWER

How powerful did the locomotives actually have to be? Let's do a simplistic reasonableness check, using the definition of "horsepower". On a level track( = horizontal), the required locomotive horsepower HPloc is (ref. 156, 157):

HPloc = W x T x S / 375

where

W = total gross train weight in tons (1000 lbs)
T = total Train Resistance (a.k.a. Starting Resistance) per ton = 8 lbs/ton. Note: this is a standard value used in the railway industry. Modern rail systems have a lower resistance.
S = speed in mph
375 is a constant that assumes that no HP is used for driving accessories (gearing, compressor, alternator, ...)

Converting this to metric units, we get:

HPloc = W x T x S / 271

where

W = total gross train weight in metric tons (1000 kg)
T = total Train Resistance per metric ton = 8 kg/ton
S = speed in km/h = mph / 1.609

Total weight of the rotating superstructure was 120 metric tons, distributed among the four locomotives and the central support at the center of the concrete ring. The locomotives carried 4/5 x 120 = 96 metric tons. Wind load would increase this value. The specified diameter of the center of the circular rail track ( = midway between the two rails) was 2x10.55 = 21.1 m (ref. 193). Hence, the track length was π x 21.1 ≈ 66.3 m. This means that at 2 rpm = 120 rph, the small locomotives moved at a respectable speed of 120 x 66.3 = 8 km per hour (5 mph). Hence, the required total locomotive horse power is 96 x 8 x 8 / 271 = 22.7 HP at the traction wheels. There is down-gearing between the motor and the driven wheels. Let's assume a reasonable transmission efficiency of 85%. For the required total motor horsepower we now get:

HPmotor-total = HPloc / 0.85 = 22.7 / 0.85 = 26.7 HP

The "Bernhard" system used four locomotives. So, the required motor horsepower per locomotive is:

HPmotor = HPmotor-total / 4 = 26.7 / 4 ≈ 6.7 HP

Note that locomotive motors did not have to drive accessory loads such as generators and blowers. Hence, traction horsepower = brake horsepower. The above derivation does not take into account a requirements to accelerate to the nominal speed within a certain amount of time!

The rolling resistance of a railway vehicle (which is a science all by itself) is the sum of all forces acting through the wheels and the axles, that oppose motion of that vehicle. There are many sources of rolling resistance. Some vary only with weight (e.g., journal bearing resistance, rolling friction, track resistance), some are linearly proportional to speed (e.g., wheel-flange contact, wheel-rail interface, lateral and vertical movement), some depend on the square of the speed (e.g., aerodynamic), and some on the fourth time-derivative of displacement. Examples:

  • Bearing friction.
  • Elastic deformation of the wheel-tread and of the rail, in the wheel-rail contact area. Note that the contact surface between a wheel and the rail is a very small elliptical area, called the "contact patch". It is typically only about 15 mm (0.6 inch) across! The weight of the wheel and the load that it carries, makes a "dent" in the surface of the rail head. This dent moves with the wheel, and is like a very small bow wave. So, trains actually always go uphill, even if the track is perfectly horizontal!
  • Losses due to wheel creep (during accelerations and decelerations, the elastic deformations cause the actual wheel displacement to be be different from its rolling distance).
  • Losses due to grinding of wheel flanges against the rail head, and "hunting" (horizontal back-and-forth waving movement of the bogies on the track).
  • Wheel noise (vibration and resonances in the wheels).
  • Suspension "jounce" (the fourth time-derivative of displacement), due to impacts on rail joints (if any), and associated rebounds. Bumps and bounces convert horizontal momentum into vertical momentum; the associated energy is dissipated in the suspension.
  • Track deformation (Rayleigh waves).
  • Aerodynamic drag that acts on exposed wheels and on the body of the locomotive. At low speed, this is normally quite small, if not negligible. However, in the case of "Bernhard", there is also drag of the large antenna system due to system movement and wind load. The antenna system is symmetrical with respect to the vertical axis of rotation. So there is a "push & pull" effect, depending on whether the movement is upwind or downwind. Wind will change the apparent weight on the locomotives.
  • Curve resistance, due to the radius of the curvature of the track. Note that regular "1 meter" gauge track typically has a minimum curve radius of 45 - 60 meters, about 4 - 6 times that of the circular "Bernhard" track! Without special measures, the curve resistance would have been quite high!
  • The "Bernhard" track had a gauge ("Spurweite", distance between the inside of the rail heads) of 842 mm. The on-center distance between the rail heads was 900 mm (≈ 3 ft). Ref. 193.

In normal rail applications, total resistance at low speed (less than about 15 km/h, 10 mph) is dominated by friction of the axle bearings (ref. 159). Note that a train with steel wheels on steel rails has a friction factor that is about 80% lower than a truck (UK: lorry) with rubber tires on pavement! Also note that the central support below the rotating superstructure had a large ball bearing (diameter ≈40 cm ≈16 inch). Clearly, it caused some rotational resistance.


DC MOTOR DRIVE

Electrically powered rail vehicles (electric and diesel-electric train locomotives, streetcars/tramways, subways) traditionally used DC traction motors. This remained the case until well after the advent of solid-state power electronics, in particular gate turn-off (GTO) thyristors, in the early 1960s. DC traction motors where primarily of the series-wound brushed type. I.e., with a commutator, and the field windings in series with the motor's armature windings. Note that brushless DC-motors only date back to the late 1950s, ref. 160.

Series DC-motors can produce their highest torque at low speed: as much as 3-8 times the full-load torque at nominal speed. This is ideal for traction applications. For a given field flux, DC motor speed is determined by the armature voltage, whereas the delivered torque is driven by the armature current.

Berhard station

Fig. 117: Basic types of wound Direct Current (DC) motors - classified by placement of the field winding


Berhard station

Fig. 118: Basic characteristics of series, shunt, and compound DC motors


As stated above, the speed of a DC motor depends on the voltage across the motor's armature and the field flux. Standard methods to vary the armature voltage of a series motor are:

  • An adjustable resistance placed in series with the motor's armature.
  • Ward-Leonard drive system.
  • Rectified adjustable AC-voltage (ref. 161, 163G).

There are many other flavors of motor speed control (variable AC frequency, Pulse Width Modulation, ...). They are generally beyond the scope of this discussion, and of the technology available at the time.

The adjustable series-resistance method (e.g., rheostat) has a major disadvantage: poor speed regulation ( = speed is highly load-dependent). There are also very high losses ( = heat dissipation) in the series resistance at low speed. That is, during speed-up from, and slow-down to stand-still. Some speed-control methods for series DC-motors are illustrated in Figure 119 and 120.

Berhard station

Fig. 119: Speed control of a series DC-motor via field or armature diverter, tapped field-winding, variable series resistance


Berhard station

Fig. 120: Speed control of a series DC-motor via series-parallel reconfiguration of split field-winding and multiple motors


The Ward-Leonard Drive System (D: "Leonardsatz", "Ward-Leonard-Umformer", "Leonard Doppel-Umformer") is basically an electro-mechanical way of generating a variable DC-voltage to control the speed of a DC-motor. Ref. 162A-162G. It was invented by Harry Ward Leonard in 1892. For about 75 years, there were few practical alternatives to this system - until the advent of solid-state power-electronics such as thyristors in the 1960s. Worldwide, this was the normal way to provide smooth, step-less control of the speed of high-power DC-motors, from zero to full speed. It has been - and still is - used in many applications, such as cannon/gun- and turret-aiming, elevators, rolling mills, cranes, hoists, mining (colliery) winders, diesel-electric propulsion of locomotives and of special ships, strip-mining shovels, and heavy radar antennas. German WW2 radar antenna systems with a Ward-Leonard drive include the "Wassermann S" (FuMG 42; see figure 2 in ref. 162G; 36-60 m tall / 4 m diameter column, weight up to 60 tons) and the AEG-Telefunken "Würzburg Riese" (FuSE 65) with its large dish antenna (7.5 m diameter, 9.5 tons; ref. 162F). Allied radar system also used Ward-Leonard drives. E.g., the 20 ton antenna of the British "Marconi Type 7" was rotated with a 15 HP DC-motor, controlled with a Ward-Leonard set comprising a 24 HP 3-phase motor, a main DC-generator, and a small DC exciter generator. Ref. 162H.

The Ward-Leonard Drive System consists of a Ward-Leonard Drive Unit and a shunt-wound DC motor. The Drive Unit consists of a motor-generator. The motor (referred to as the "prime mover") has a near-constant speed. This can be a 3-phase or single-phase synchronous AC motor, or a combustion engine (diesel, gasoline/petrol) with a speed governor. The output shaft of the motor is coupled (direct-drive) to the input shaft of a DC-generator. The output voltage of this DC-generator is connected to the armature of the DC-motor that drives the load. The DC-motor need not be located near the motor-generator. The shunt-field of the DC-motor is connected to a constant voltage source; hence, the motor's excitation field (flux per motor-pole) is constant, and the torque only depends on the armature current - independent of the motor speed. The shunt-field of the DC-generator is connected to that same constant-voltage source, though via a rheostat (large variable resistor).

Berhard station

Fig. 121: Ward-Leonard Drive System


The generator's output voltage is varied by changing the generator's field current with the rheostat. In turn, this changes the DC-motor's armature voltage, and hence its speed. The constant voltage source may be a rectified AC voltage (if the prime mover is an AC-motor). It can also be generated with a small DC exciter-generator ("selbsterregter Erregergenerator"), that is also driven by the prime mover, and has its shunt-field connected to its own armature (hence, "self-excited").

The Ward-Leonard drive unit is an electro-mechanical multi-kilowatt amplifier: a small change in the input current (generator field) results in a large change at the output (generator armature voltage and current). However, in its basic form, it is an open-loop control system: the rotational speed of the load is not measured and fed back in order to adjust the generator's field current. Hence, that speed is not regulated with the high precision required in the "Bernhard" application. Note that it is possible to expand the basic Ward-Leonard system with such a feedback loop.

Another drawback is that both the AC-motor (or the engine) and the DC-generator must be dimensioned for the full and peak power of the load-driving DC-motor(s) and system inefficiencies.

System efficiency is driven by the product of the efficiency of the three machines (AC-motor, DC-generator. DC-motor), and typically lower than that of rheostat control and field control methods. A single Ward Leonard drive unit can control multiple load-sharing DC motors in parallel ("group control"). Variations of the Ward-Leonard drive system are electro-mechanical amplifiers such as the Metadyne (1930s) and the Amplidyne (1940s).

As elegant and effective as the Ward-Leonard drive system may be, it was not what was used in the "Bernhard" to provide a variable DC-voltage to the locomotive drive system! The DC motors were regulated with series rheostat for speed up from standstill and down to standstill.


SYNCHRONOUS AC MOTORS

There are two basic types of AC motors: asynchronous motors and synchronous motors. Both have two main parts: a stator and a rotor. In a 3-phase motor (synchronous or asynchronous), the stator basically consists of triple pairs of formed coils of wire. Each coil is mounted in the slots of a laminated steel core. The coil pairs are spaced evenly around the stator. See Fig. 122. The two coils of each pair are connected in series.

Berhard station

Fig. 122: Simplified cut-away view of the stator of a 3-phase AC motor (synchronous or asynchronous)


Each coil-pair is energized by one phase of the 3-phase AC electrical power. Each energized coil-pair forms a pair of magnetic poles. The resulting magnetic field extends into the air gap between the stator and rotor, and into the rotor. The magnetic field strength and polarity of each pole-pair changes cyclically, as the AC excitation is sinusoidal. When all three phases are connected, the stator generates a rotating magnetic field (RMF). This field has a constant amplitude, and rotates with the same speed as the 3-phase excitation. E.g., for an excitation frequency of 50 Hz = 50 cycles/sec, the RMF rotates at 50/sec x 60 sec/min = 3000 rpm, and at 3600 rpm for 60 Hz excitation.

Berhard station
Berhard station

Fig. 123: Concept of how an RMF is generated by a 3-phase stator when excited with 3-phase AC power


We all know that unlike magnetic poles (North-South) attract each other, and like magnetic poles (North-North, South-South) repel each other. The motor's rotor can turn freely inside the stator. Let's take a rotor that consists of one or more magnetic pole-pairs. The stator generates a rotating magnetic field, so the magnetic rotor poles will try to remain aligned with that field: the rotor turns. There are several ways to make a stator pole-pair, see Fig. 123:

  • A permanent magnet (bar magnet).
  • A coil with the ends short-circuited. By itself, such a coil does not generate a magnetic field. However, if a varying magnetic flux is induced in this coil, a current will circulate in the coil. The direction of this current is such that it opposes its cause (Lenz's Law). The cause is the varying induced flux. With the RMF of the stator, the induced flux in the rotor winding only varies if the rotor does not turn at the same speed as that RMF. This induced varying flux, combined with the induced current, generates an electro-magnetic force (EMF, Faraday's Law) that acts on the coil conductors. The magnitude of the torque ( = rotating force) is proportional to the relative rotational speed of the rotor, compared to the synchronous speed ( = the speed of the RMF). The speed difference is called "slip". The direction of the torque is such that torque is reduced (remember: Lenz' Law): in other words, such that the speed difference is reduced.
  • Important: there is no rotational force if the rotor turns at the synchronous speed! Hence, the rotor never turns at the synchronous speed, but always slower. The amount of slip depends on the mechanical load that is driven by the motor. The heavier the load, the larger the slip ( = lower motor speed). If the load varies, the speed varies. An AC motor with such a rotor is called an asynchronous motor. As it works on the principle of induction, it is also called an induction motor. Low-power asynchronous motors can have a slip of 5-10%, whereas asynchronous motors with a higher power rating have approx. 2-5% slip.
  • The rotor coils can be implemented as actual coiled wires (in which case the rotor windings are typically made accessible via slip rings), or simply be implemented as so-called "squirrel cage" (two parallel metal rings with a number of evenly spaced metal bars between them, often at a skew angle).
  • A coil that is energized by a DC voltage. This is equivalent to a permanent magnet. As the rotor has to turn, the DC power is supplied via slip rings. When the rotor is at standstill or at low speed, the alternating polarity of the stator's rotating magnetic field (RMF) sweeps by the poles of the rotor relatively fast. Each rotor pole is cyclically briefly pulled into one direction (without producing sufficient starting-torque), and than briefly in the opposite direction. The rotor may vibrate but will not turn!
  • Important: a motor with such a stator is inherently not self-starting! The motor needs a supplemental drive mechanism (e.g., a starter winding incorporated into the motor, or another motor) to first be accelerated to 90-95% of the synchronous speed (i.e., < 5-10% slip) - without energizing the rotor. At that point, the rotor is energized and automatically pulls into synchronism (a.k.a. "in step") with the RMF: the rotor poles are locked to the RMF and the rotor turns at synchronous speed. This is great for a constant speed drive application: no need for a closed-loop speed control system! For obvious reasons, a motor with such a rotor is called a synchronous motor.
  • Important: a synchronous motor turns at the exact synchronous speed, from no-load to full-load!
  • Contrary to the asynchronous motor, the motor torque is generated as a result of the physical angle between the stator and rotor. This phase angle is called the load angle, coupling angle, or torque angle. An increase in mechanical load causes this angle to also increase - but synchronous speed is maintained! If the mechanical load ever exceeds the motor's maximum torque, the rotor completely loses synchronism (drops "out of step") with the stator's RMF, and the motor comes to rest. The same happens if the rotor supply voltage or the stator supply voltage is reduced excessively.
  • For a constant load, the motor's EM torque is equal to the load torque and the torque angle is a non-zero constant. A sudden change in load will upset this steady state. The locking between the rotor and the RMF is not rigid! A sudden increase in load causes a temporary slow down of the rotor, which simultaneously increases the torque angle and the EM torque. This accelerates the rotor back to the synchronous speed. As the rotor reaches synchronous speed again, the torque angle is larger than needed and the rotor speed overshoots the synchronous speed. This reduces the torque angle, and the EMF torque drops simultaneously. The rotor decelerates and the rotor speed now undershoots the synchronous speed, etc. I.e., the rotor speed oscillates around the sync speed. This phenomenon is known as "hunting" and "phase swinging". Under certain conditions, these oscillation may diverge ( = exponentially increase in amplitude), even to destructive levels. The oscillation can be reduced by adding damping windings (a.k.a. amortisseur windings) to the rotor, and by large load inertia (e.g., a heavy flywheel, or the rotating structure of the Bernhard system).

Berhard station

Fig. 124: Possible configurations for a pole pair of an AC motor


The following graphs show the torque-versus-speed characteristics of an asynchronous and a synchronous AC motor:

Berhard station

Fig. 125: Torque-vs-speed characteristic of a typ. asynchronous AC motor (left) and of a synchronous AC motor


The synchronous rotor speed of an AC motor is clearly proportional to the RMF that is generated by the stator, i.e., to the frequency of the AC excitation of the stator. However, it also inversely proportional to the number pole-pairs of the rotor. The simple formula is given in the figure below. For instance, for a 50 Hz excitation, the synchronous rotor speed Ns is 3000, 1500, 1000, and 750 rpm, for 1, 2, 3, and 4 pole-pairs, respectively. The number of pole-pairs is an integer value, so it obviously cannot be chosen as freely as an excitation frequency. Compared to asynchronous motors of equal power and speed, synchronous motors are attractive for low-speed ( < 300 rpm) and ultra low-speed drive applications: their efficiency is high, their power factor can always be adjusted to 1 (via field current adjustment), and they are less costly.

Berhard station

Fig. 126: Synchronous motor rotors with 1, 2, & 3 pole-pairs and slip-rings for DC power

(rotors shown with salient ( = protruding) poles, typ. for low speed applications, rather than cylindrical rotor with distributed windings)

The characteristics of the synchronous motor of "Bernhard" locomotive nr. 4 are not known: neither the frequency of the 3-phase AC (other than "mid-frequency", which is typ. 400 - 2000 Hz), nor the number of rotor poles, nor the torque rating.


At least one of the locomotive motors of the Be-13 station at Buke was built by Ziehl-Abegg Elektrizitätsgesellschaft m.b.H., of Berlin-Weißensee. It was a 10 kW (13.6 metric horsepower, 13.4 US hp) "low rpm" motor (ref. 99). This suggests that it may have been the synchrounous AC motor. The motors at (some) other Bernhard stations may have been built by Siemens (e.g., ref. 103). This was probably Siemens-Schuckert, who also manufactured electric locomotives.

Ziehl-Abegg is a company specialized in electric motors. It was founded in 1910 by Emil Ziehl and the Swedish investor Eduard Abegg as Ziehl-Abegg Elektrizitäts-Gesellschaft m.b.H. Abegg dropped out of the partnership the same year, as he could not come up with the required funds, and the patent that he brought into the deal (ref. 214) proved useless. However, Abegg's initial "A" was retained (as a solid triangle) in the the "Z-A" company logo. Ref. 154. In 1897, Emil Ziehl invented the external rotor motor ("Außenläufermotor", outrunner motor: stator inside the rotor - very compact and excellent weight balancing). In 1904, he invented electrically powered gyroscopes with gimballed suspension. Prior to 1910, Emil Ziehl had developed electric motors and tested generators at AEG, and developed gyro-compasses at Berliner Maschinenbau AG (BEMAG, frmr. Eisengießerei und Maschinen-Fabrik von L. Schwartzkopff). BEMAG was a manufacturer of locomotives powered by steam, compressed air, and electricity. Ziehl-Abegg made DC-DC converters (DC-motor + generator) for Zeppelin airships and airplanes. Telefunken was a major customer. They also made electro-mechanical transverters ("Drehstrom-Gleichstrom-Umformer", i.e., AC-motor + DC-generator, as in Ward-Leonard Drive Systems) for elevators and generation of anode voltage of large transmitters, transformers for directional-gyros (e.g., SAM-LKu4), motor-generators such as the U 4a, and the motor-generator-alternator of the U 120 of the "Bernhardine" system. After the war, the production facilities were carried off to the Soviet Union. In 1947, the company restarted, this time in the south of Germany (some 70 km northeast of Stuttgart). These days, Ziehl-Abegg AG is a manufacturer of electric motors for elevators, ventilation and air-conditioning systems.

Ziehl-Abegg

Fig. 127: 1912 advertizing poster, listing in 1943 Berlin phonebook, wall plaque on the building in Fig. 109

(source of poster: ref. 155)

Ziehl-Abegg

Fig. 128: Ziehl-Abegg postmark on an envelope - 1938

(source: www.briefmarken12.de)

Ziehl-Abegg

Fig. 129: Company buildings of Ziehl-Abegg Elektrizitätsgesellschaft m.b.H in Berlin-Weißensee

(source: unknown


THE LOCOMOTIVE MOTOR CONTROL SYSTEM

The task of the locomotive motor control system is to smoothly increase the rotational speed of the "Bernhard" beacon from stand-still to exactly 2 rpm, and to accurately maintain that speed. The signals transmitted by the "Bernhard" beacon were printed aboard the aircraft with the "Bernhardine" Hellschreiber-printer. The compass-scale channel of this printer was synchronized to pulses transmitted by the beacon. As explained in the "Optical Encoder Disk" section (after Fig. 79), to make this synchronization scheme work, the allowed tolerance on the 2 rpm beacon speed was only ±0.2-0.3 % (p. 80 in ref. 181 and p. 8 & 18 in ref. 183). This small tolerance had to be met, independent of variations in the motor load (e.g., rail resistance around the circular track, wind load), and independent of amplitude and frequency variations of the 3-phase 50 Hz primary AC power. Note that towards the end of the war, the minimum frequency of the 50 Hz power grid was reduced to 43.3 Hz in the Central German block, and to 41 Hz in the Western German block (ref. 14).

One standard way to control and regulate motor speed is with a closed-loop control system. This requires tachometer feedback of the momentary speed, for comparison against the speed set-point. The amount of speed error (and possibly one or more of its time derivatives, and its integral) is then used to command the motor to speed up, or slow down. If the control system is properly configured and dimensioned ( = control laws/algorithms), and it has sufficient control authority ( = "power"), then the torque-vs-speed curve of such a drive system can be made to approach that of a synchronous motor (see Fig. 125 above, ref. 215). So, when constant speed is required - as is the case here - then why not go straight to an inherently synchronous AC motor drive and use an AC power source that has a sufficiently constant frequency? Yes, indeed, why not! Doesn't this basically just move the control system from the motor to the AC generator? Yes, indeed. But there it is easier to implement, as we shall see.

On the one hand, the locomotive drive system must operate with 3-phase primary AC power that has varying frequency and amplitude. On the other hand, DC power ( = rectified AC power) is required for several reasons. First of all, as explained in the "synchronous AC motors" section above, a synchronous motor is not self-starting. It must be brought close to synchronous speed by other means. Here: with DC traction motors. Also, the field winding of a synchronous AC motor is DC-powered. So, a 3-phase AC rectifier is required. And to complete the synchronous AC drive system, we need a "DC to fixed-frequency 3-phase AC" converter.

The next diagram illustrates the three main blocks of the "Bernhard" locomotive drive system:


Bernhard wiring

Fig. 130: Top-level block diagram of the "Bernhard" motor drive system

(source: derived from ref. 189, 190)


The "Electrical power control, conversion & distribution" block has the following functions and associated control panels:

  • Selection of the source of 3-phase 50 Hz (nominal) AC main power: the public power grid, or the local generator of the “Bernhard” station.
  • Protection against over-voltage / over-current conditions of the primary AC power, and emergency shutdown. For the latter, there was a shutdown button located in the rotating cabin, in the round building below it, and outside the concrete ring.
  • Conversion of the selected 3-phase 50 Hz AC power to DC power. This was done with a 6-anode Mercury Arc Rectifier described further below.
  • Conversion of DC power into 3-phase AC power that has a constant frequency (unlike the primary AC power). This conversion was done with an electro-mechanical DC-AC inverter; in this case, a so-called "Conz" converter as described further below.
  • Distribution of the AC and DC power. The selected 3-phase 50 Hz AC main power is distributed to the rectifier unit and to the rotating cabin (via a slip ring assembly in the round building below that cabin). The DC power from the rectifier unit is distributed to the DC-AC inverter and to the rotating cabin, Also see the "Electrical & signal distribution" section.

The motor drive control panel was located in the rotating cabin. It had separate controls for the three motor types (main drive DC, auxiliary drive DC with separate field winding, and synchronous AC). The block diagram in the next figure illustrates the power conversion and motor drive control functions with more detail:

Bernhard wiring

Fig. 131: Electrical power and signal interconnections of the locomotive system

(source: derived from ref. 93, 189, 190)


The four main-drive DC motors were controlled via a heavy-duty variable resistor arrangement in series with the field and armature windings of each motor. The controller and resistor bank ware located in the rotating cabin (see the hand wheel on the "Main Drive" control panel in Fig. 132 below). The three auxiliary-drive DC motors had a separate field winding that was wired to the "Auxiliary Drive" control panel. The field current was also controlled with a variable resistor, but with a much lower power rating than that of the main-drive motors.

Berhard station

Fig. 132: German engineer showing the locomotive control panel of Be-9 at Bredstedt to a member of the RAF-ADW

(source: Australian War Memorial photo SUK14636, public domain; ca. August 1945)

Each locomotive had two motors and two bogies. Most likely (but unconfirmed), each bogie had one motor. Each bogie had two axles. It is unclear if only one axle of each powered bogie was driven, or both axes (better traction, but mechanically more involved). At least one bogie of one locomotive had external gearing, with a belt or chain:

Bernhard wiring

Fig. 133: External gearing on a locomotive of Be-4 at La Pernelle

(source: 1946 film clip of Be-4 at La Pernelle, Cinémathèque de Normandie)

Since the synchronous AC motor provided inherent accurate speed control, there was no need for a closed-loop speed control system with a speed sensor. But there were two speed sensors: a tachometer in locomotive nr. 4 (with the synchronous AC motor), and a tachometer track on the optical encoder disk (measurement accuracy 0.1%) in the round building below the rotating cabin and superstructure. However, they were there for speed monitoring and alerting purposes only.



MERCURY ARC RECTIFIERS

A rectifier is an electrical device that converts alternating current (AC) to direct current (DC). The device achieves this by allowing electrical current to flow through it in one direction only. A half-wave rectifier only passes either the positive or the negative half of a full AC voltage cycle. A full-wave rectifier passes the positive half cycle directly, and the negative half cycle with inversed polarity:

Berhard station

Fig. 134: Half-wave and full-wave rectification of single-phase and 3-phase sinusoidal AC voltages

(assumes ideal rectifiers/diodes (no forward voltage drop, etc.), no source reactance (typ. inductive), no output smoothing, and no load)

By 1930, the Mercury Arc Rectifier (MAR, a.k.a. Mercury Vapor Rectifier; D: "Quecksilberdampfgleichrichter", ref. 163A-163R) had become the best method for rectifying high power AC voltage in industrial applications and electrification of light and heavy railroad. The discovery of the unidirectional current-flow of an atmospheric arc between a mercury pool and a carbon electrode, goes back to 1882 (Jules-Célestin Jamin and his co-worker Georges Maneuvrier, ref. 163H). The MAR was invented around 1900. P. Cooper-Hewitt patented a glass-envelope MAR in 1902 (ref. 163J), based on his mercury vapor lamp. He marketed a metal-envelope MAR in 1908. In 1914, Irving Langmuir patented the concept of using a control-grid between the anode and the mercury-pool cathode (ref. 163K). This made it possible to arbitrarily choose the actual moment of arc initiation ( = switch-on via phase angle control, instead of it being determined by the primary power), and thereby vary the DC output. MARs can also be configured as an inverter instead of a rectifier, i.e., as a DC-to-AC converter.

MARs are a form of cold-cathode gas discharge tube. The rectifier consists of a glass or stainless steel vessel. The vessel is evacuated, or filled with inert gas. There is a pool of liquid mercury at the bottom of the vessel. This is the cathode. The vessel has one or more upward arms with a graphite anode. Clearly, a MAR is a static rectifier, as opposed to the mechanical rotary converters that preceded the MAR.

Full-wave rectification of a single-phase AC voltage requires two anodes. See Figure 135. For rectifying 3-phase AC power, the MAR must have a multiple of three anodes.

Berhard station

Fig. 135: left: Simplified principle diagram with a 2-anode MAR (left) and an active 3-anode MAR


Like a fluorescent lamp, a MAR must be started. Conduction is initiated by dipping the starting (igniting) electrode into the mercury pool, passing a high current, and retracting the electrode. This locally heats up the mercury (the "cathode spot" or "emission spot") and vaporizes it. This starts abundant emission of electrons by the mercury cathode. The mercury vapor is ionized by the stream of electrons that flows to the anode, and causes plasma discharge (arc) between the anode and the cathode. The mercury ions emit both visible blue-violet light, and a large amount of ultra-violet radiation. The light may have another color when the vessel is filled with an inert gas, e.g., pink as in Fig. 125 (probably argon). Evaporated mercury condenses on the cool wall of the vessel (hence the large bulbous form), and returns to the mercury pool at the bottom of the device. The plasma discharge stops as soon as the anode voltage drops below a certain level, or anode current is interrupted. Hence, for rectification of an AC voltage, ignition must be synchronized with that voltage. Alternatively, excitation electrodes may be used to maintain the plasma. The anode material does not emit electrons, so electrons can only flow from the cathode to the anode. I.e., current can only flow from the anode to the cathode. The ripple on the DC output current is smoothed with a series-inductance ("choke coil").

The heat of the mercury vapor must dissipate through the glass envelope in order to condense. To help keep the glass envelope cool enough, an electric fan is typically installed below the MAR (as clearly visible in Fig. 138 and the the right-hand photo of Fig. 140 below).

Berhard station

Fig. 136: Effect of cooling on voltage vs. current curve ( = losses & efficiency) of a glass MAR

(source: Fig. 66 in ref. 192)

For operating temperatures below 10 °C (50 °F), special measures must be taken to protect the MAR against damage from instable operation, and the attached transformers against current surges. This may be done with surge diverters and cathode heating. Ref. 161. Note that mercury freezes around -39 °C (-39 °F).

The MAR anodes are connected to AC power via a transformer. Each phase of the secondary side of this transformer has an inductance: inductance of the secondary winding itself, and transformed inductance of the primary transformer windings and the AC power line. Inductance prevents current (here: anode current) from varying instantly. Hence, when one anode becomes conductive and its current is building up, the current of the adjoining previously conductive anode anode is still dying down: for a short time, both anode arcs are active simultaneously! This cyclic "overlap" phenomenon effectively short-circuits the main transformer's secondary phases that are associated with these anodes. For rectifier circuits, the "overlap angle" (a.k.a. commutating angle) is the commutation time interval when when both devices conduct. This causes the rectifier's DC output wave to temporarily drop to the average of the overlapping sinusoidal transformer phase voltages, which significantly distorts the ripple (Fig. 25, 29, 33, 37 in ref. 163C).

Berhard station

Fig. 137: The effect of phase-overlap on the DC voltage wave

(overlap due to source reactance or load; source: Fig. 25 & 29 in ref. 163C)

The voltage drop during the overlap period is proportional to the output current, and is also a function of the number of anodes and of the transformer inductance. As load current is increased, the operating time (duty cycle) of each rectifier phase is increased, and more phases will overlap. In case of a short-circuit load, the significant voltage drop across the rectifier arcs and resistive losses in the transformer (and other parts of the rectifier circuit) prevent full-time overlap of all phases.

MARs can be constructed for hundreds of kilovolts and tens of thousands of amps. They have been used, and sometimes still are (!), as rectifiers for locomotives, radio transmitters, control of industrial motors, welding equipment, aluminum smelters, high-voltage DC power transmission, etc. Glass-bulb MAR designs are typically limited to 250 kW (500 volt, 500 amps). For higher power levels, a steel-tank version was developed around 1908. Siemens-Schuckert developed a compact double-wall water-cooled tank rectifier around 1920. Through the 1960s, high power (up to gigawatts, ref. 163L) high-voltage DC (HVDC) transmission line systems were designed with MAR rectifiers and inverters. MAR technology was succeeded by ignitrons and thyratrons (ref. 163F), and then solid-state Gate Turn-Off devices (GTOs, e.g., thyristors),ref. 163Q.

In May of 2015, I obtained the black & white photo shown below. It shows the large 6-anode MAR of the Be-10 "Bernhard" at Hundborg/Denmark. The MAR does not appear to have control-grid electrodes. It was installed in a typical MAR-cubicle, 2 m tall (≈ 6.7 ft). The required primary transformers were located in the adjacent MAR-control cabinet. Likewise, the choke-coil, though the DC-motors may have had enough inductance so as not to require such a DC-current smoothing coil.

Berhard station

Fig. 138: The rectifier system of Be-10 at Hundborg/Denmark

(sources: (left) ref. 223; (right) Fig. 31 in ref. 93A; the thick "disk" below the MAR is actually the spinning cooling fan)

The "Bernhard" MAR was made by the Gleichrichter Gesellschaft m.b.H company in Berlin, manufacturer of rectifiers since 1919. They were acquired by the Swiss company Brown-Boveri & Cie. (BBC) in 1921 (ref. 191). BBC became ABB (ASEA Brown Boveri), after a merger between BBC and ASEA AB of Sweden in 1988. The "Bernhard" MAR was a model S 18 T "Glasgleichrichterkolben" (glass bulb rectifier; pdf page 20 in ref. 189). The complete rectifier cubicle with all the equipment and controls was model DRA 300A / 220 V, also of the Gleichrichter G.m.b.H. (pdf page 20 in ref. 189). The model designator suggests that the MAR had a rating of 330 amps DC at 220 volt AC. The cubicle included the standard cooling fan as well as a bulb heater. The circuitry around this MAR included 17 fuses! Standard equipment of each "Bernhard" station included one spare MAR (pdf page 21 in ref.189).

Berhard station

Fig. 139: Label of a BBC MAR-cubicle with a MAR built by Gleichrichter G.m.b.H. in Berlin

(source: H.-T. Schmidt homepage; MAR for 220 volt 3-phase AC @ 75 amps, 100/140 volt DC @ 150 amps, 140/165 volt DC @ 65 amps)

Other German MAR manufacturers of the era included Siemens-Schuckert Werke, several German subsidiaries of BBC, and the AEG company Apparate-Werke Berlin-Treptow (AT) that was founded in 1928. A 6-anode MAR with a height of 90 cm (3 ft, about the size of the "Bernhard"-MAR) can typically handle as much as 350 amps at 650 volts. The photo on the left in Fig. 140 below shows a small MAR, rated for only 220 volt / 100 amps (22 kW), together with its transformers. This MAR was manufactured in the 1950s by Elektro-Apparate-Werke J.W. Stalin in Berlin-Treptow. This was the post-war continuation of AEG-AT in the Soviet-occupied part of Germany. The 6-anode MAR in the photo on the right is about 60 cm (2 ft) tall. It is part an elevator (lift) system in a defunct very large WW2 air-raid shelter 140 ft (43 m) below Belsize Park in London (ref. 243). This MAR is still operational in modern days (at least through the year 2014). The cubicle is similar to the "Bernhard" cubicle in Fig. 138.

Berhard station

Fig. 140: Example of MAR cubicles (left: 1950s, right: 1936)

(sources: collection of Technical University Freiberg(left); ©2000 Nick Catford Subterranea Brittanica (ref. 243); both used with permission)

The "Bernhard" MAR shown in Figure 128 has six anodes. For obvious reasons, these multi-arm MARs are sometimes referred to as "Krakengleichrichter" ("octopus-rectifiers"). Compared to a 3-arm MAR, a 6-arm MAR reduces the ripple in the rectified voltage. It also requires a more complicated main-transformer connection to AC power, e.g., a delta/double-star or star/double-star configuration. See pp. 18-24 in ref. 163B. Six-anodes is typically sufficient. Having more anodes does reduce the output ripple (which has a lowest harmonic frequency of six times the 50 or 60 Hz main power). However, the reduction when going from 6-phase to 12-phase rectification is less than half the reduction when going from 3-phase to 6-phase (Fig. 35 in ref. 163C for no-load conditions). Also, cost increases rapidly without increasing rectifier output, and the already low power factor (due to an undesirably large phase angle between AC supply voltage & current) is further reduced.

Berhard station

Fig. 141: A 6-anode Mercury Arc Rectifier with delta/double-star main-transformer connection to 3-phase AC power

(source: Figure 7.41 in ref. 163E)

When the motor voltage is reduced to slow down the motors (e.g., to brake to standstill), the large inertia of the "Bernhard" turntable will reverse the load torque of the motors. However, current can only flow through the MAR in one direction - it is a rectifier/diode. So, regenerative braking ( = using the motor as a generator and feeding the generated electricity back to a power grid) is not an option, and the motor cannot exert a braking torque. As a result, the armature voltage will increase to undesirably high levels. This is typically handled by switching-in a large dummy-load resistors across the armature of the motors, and dissipating the generated power as heat.

Here is a 36 sec video clip of a 6-anode MAR in action (you may want to turn the audio volume down a bit - MAR systems are very loud!):

A six-anode Mercury Arc Rectifier in action

Source: YouTube; one of four MARs of the 750 volt DC power supply system of the tramway network in Melbourne/Australia. MARs made by Hewittic Electric Co. (frmr. Westinghouse Cooper-Hewitt Co Ltd.) in Walton-on-Thames/England, and installed in 1936.


THE "CONZ" DC-AC POWER INVERTER

As stated above, a synchronous AC motor was used for obtaining and maintaining the required accurate locomotive speed. The frequency of the 3-phase AC power from the public power grid and the local backup generator was not sufficiently accurate. Hence, the fluctuating primary AC power had to be converted to constant-frequency 3-phase AC. Before the days of solid-state power electronics (1960s), the required power conversion was done by electro-mechanical means: an electric motor, an AC generator, and a closed-loop control system. The motor, generally referred to as the "prime mover", could be AC or DC. In the "Bernhard" system, a special DC-to-3-phase-AC inverter (D: "Umformer für Gleichstrom-Drehstrom") was used: a model NGJV So, 5/2 T built by the Conz company (sheet 16 in ref. 189). It was located in power generator building near the "Bernhard" beacon. The associated control panel had the following fuses: two for 350 V, 160 A, and three for 500 V, 35 A (per sheet 20 of ref. 189).

The Conz Elektricitäts-Gesellschaft mbH company was founded in 1887 by Gustav Conz. It was originally located in the Spaldingstraße in the southern German city of Ulm. The company moved to Hamburg in 1890, and acquired a plot of land in Hamburg/Altona-Bahrenfeld (Gasstraße 6-10) in 1911. An office building and two factory building were constructed here in 1912. Ref. 207. In 1962, Conz became a wholly-owned subsidiary of Deutsche Maschinenbau-Aktiengesellschaft (DEMAG) in Duisburg. The Hamburg plant was closed in 1995.


Conz Hamburg

Fig. 142: advertizing of the Conz company from 1924

(source: Elektrotechnische Zeitung (ETZ), Nr. 16, 17 April 1924)

Conz Hamburg

Fig. 143: advertizing of the Conz company from 1937 & 1940


A standard AC-generator has a field winding that is fed with DC power, and an armature winding that outputs the generated AC power. That is: a "singly-fed" generator. However, at the heart of a Conz converter is a high-power "doubly-fed AC generator" (D: "Doppeltgespeister Drehstromgenerator"). This is also called a "doubly-fed induction generator (DFIG) and "slip-ring generator" (D: "Schleifringläufergenerator"). Note: "doubly-fed" is somewhat of a misnomer, as it does not mean that the machine has two separate power inputs. Just that it has two sets of 3-phase connections. A DFIG is similar to the singly-fed generator, in that the stator outputs the generated AC power. However, now the rotor is excited with 3-phase AC power at variable frequency. The frequency of this AC excitation power is continuously adjusted to compensate for changes in the speed of the prime mover. The result is regulated 3-phase AC power (D: "geregelter Drehstrom") with a constant frequency. In modern times, DFIGs are widely used for large wind turbines, as solid-state inverters required for megawatt-scale wind turbines are larger and more expensive.

Conz Hamburg

Fig. 144: singly-fed and doubly-fed 3-phase AC power generator

(the stator windings and DFIG rotor windings are shown in the standard WYE (a.k.a. "Y", star") configuration rather than Delta ("Δ"))

The next figure shows the principle diagram of the AC-AC Conz generator, as patented in 1937:

Conz Hamburg

Fig. 145: Conz convertor - variable-to-fixed frequency AC-AC converter

(source: adapted from the 1937 Hans Gross / Conz patent nr. 692583; see ref. 188 for a list of related patents)


The green overlay in the figure above, shows the control loop for keeping the output frequency of the DFIG constant - independent of variations of the frequency and voltage of the primary AC power and the output load: the 3-phase AC output power drives a synchronous AC motor. This motor is small (low power) compared to the DFIG and the primary mover. It drives a centrifugal governor. Based on the rpm, the governor adjusts a variable resistance. The resistance is placed in series with the field of a small DC motor, so as to change its speed. The DC motor drives a small 3-phase AC generator that excites the DFIG. Note that it is also possible to reverse the rotational direction of the three phases of the output. The efficiency of a Conz generator is higher than Ward-Leonard converter, especially under partial load or no load (idling).

The Conz generator configuration above uses an AC motor as prime mover, and a DC generator. This configuration can be simplified if a high-power DC source is available. This is the case in the "Bernhard" system, for powering the DC motors in the four locomotives. The DC-to-AC converter configuration is also mentioned in the Conz patent. So, a DC motor was used as prime mover, and the small DC generator was eliminated:


Conz Hamburg

Fig. 146: Conz generator - DC-AC configuration as probably used in the "Bernhard" motor drive

(source: adapted from the 1937 Hans Gross / Conz patent nr. 69258; see ref. 188 for a list of related patents)

The output frequency of the "Bernhard" Conz-generator is not known. However, the title of the related 1937 Reichs patent is "Frequenzwandlergruppe zur Erzeugung konstanter Mittelfrequenz", i.e., "Frequency converter for generation of constant mid-frequency". In modern times, 400 - 2000 Hz mid-frequency AC is used in high-power application such as resistance welding.

The photo below was taken in the power supply bunker or barrack of Be-10 at Hundborg/Denmark. The Conz converter is on the right and is about 2 m tall. It is installed upright, probably due to the centrifugal governor. The cabinets on the left house the MAR rectifier and associated circuitry and controls.


Berhard station

Fig. 147: The Be-10 Hundborg installation - cabinets with the MAR and its controls, and the "Conz" generator

(photo courtesy Mike Dean, US National Archives & Records Adm. (NARA) image nr. 111 SC 269041; US gov't = no ©)


THE ROUND CENTRAL-SUPPORT BUILDING

At the center of the concrete ring of the "Bernhard" beacon, there is round brick building with a flat concrete roof:

Bernhard

Fig. 148: Concrete ring with central- support building


Bernhard

Fig. 149: Left-to-right - the round building of Be-7 at Arcachon, Be-14 at Aidlingen, and Be-3 at Le-Bois-Julien

(photo Le-Bois-Julien: ©2006 T. Oliviers, used with permission)

Bernhard

Fig. 150: The round building of Be-8 at Bergen/Schoorl (left), and Be-12 at Nevid/Plzeň

(sources: photo Be-8: ref. 127; Be-12: © Jacek Durych, used with permission)

This small building has two functions:

  • Central support for the heavy rotating superstructure ( = cabin and antenna systems) of the beacon.
  • Stationary equipment room (D: "feststehender Geräteraum").

EQUIPMENT ROOM

The following items were installed in this equipment room below the rotating superstructure (see Figure 151):

  • A 15-ring slip-ring assembly, suspended from the ceiling of the equipment room. Slip-rings allow electrical lines to traverse continuously rotating mechanical joints. The rotor of the assembly was driven by a shaft that descended through the ceiling of the equipment room (see Fig. 161) and rotated with the superstructure. The slip-rings passed electrical power and signals between the stationary equipment room and the rotating cabin above it.
  • Optical encoder disk assembly, suspended from the slip-ring assembly and driven by the shaft of that assembly.
  • Three audio tone modulators:
  • a constant 1800 Hz audio tone for the pointer beam transmitter
  • 2600 Hz audio tone pulses, representing the compass scale in Hellschreiber format, for the compass scale transmitter.
  • 2600 Hz audio tone pulses, representing the command-message text string in Hellschreiber format, for the compass scale transmitter (when replacing transmission of the compass scale with the command-message).
  • Two Hellschreiber printers (the same HS 120 printers as used in the aircraft), for printing:
  • the signals transmitted by the beacon, as received by a remote receiver.
  • the command-message text string, to verify it before actually transmitting it (only installed at a few beacons).
  • A patch board and associated patch cord, for composing the up to 10 characters of the command-message (only installed at a few beacons).
  • A power distribution and control panel. The panel also indicated the exact rotational speed of the optical disk (and, hence, of the beacon), as measured by a tachometer track on that disk.
  • A switch for selecting the forward/reverse rotational direction of the beacon.
  • An emergency shutdown button.

Bernhard wiring

Fig. 151: The round building below the rotating superstructure - equipment and interconnections

(source: derived from ref. 189 and 190)

The photo below is the only one that I have of the inside of the equipment room:

Bernhard transmitters

Fig. 152: Equipment inside the round brick equipment room of the Bernhard installation at Hundborg

(source: Figure 30 in ref. 93A)

The 15-ring slip-ring assembly passed the following electrical power to the rotating cabin:

  • DC, for the DC motors in the four locomotives. The associated fuses had a rating of 160 A / 500 V (ref. 189).
  • 3-phase AC, constant frequency. Used for the synchronous AC motor in locomotive nr. 4. The associated fuses were rated at 80 A / 500 V.
  • 3-phase AC, nominally 50 Hz (directly from the public power grid or a local backup generator). Used for the power supplies of the two transmitters, as well as general lighting and heating.

The slip-ring assembly passed the following other signals to and from the rotating cabin:

  • Constant-tone audio modulation for the pointer beam transmitter.
  • Hellschreiber tone-pulse audio modulation for the compass scale transmitter.
  • Quadrant-keying ("Sektortastung") to both of the transmitters, by a switch contact that is actuated by a notched disk on the shaft of the slip-ring assembly. Most likely, this was (or could be) used to not transmit during the entire 360° rotation, but only in a specific limited directional range. This could be used to avoid detection of transmissions by Allied monitoring stations, e.g., in Britain. Beacons operating this way were referred to as "Sektorfunkfeuer" (p. 16 in ref. 181).
  • Switch closure of the emergency shutdown button on the superstructure.

No photos are available of the slip-ring assembly. As an example, the photo below shows the slip-ring assembly of German "Panther" and "Tiger" tanks of the same era. Their slip-rings have a diameter of 12 cm (≈5 inch). There are four brass rings for electrical power (12 & 24 volt, 50 amps) and seven rings for communication and lighting.

Bernhard

Fig. 153 The slip-ring stack of Panzer V "Panther" and VI "Tiger" tanks

(source: ref. 145)

The standard "Bernhard" equipment included a full set of 52 spare tubes (valves), per sheet 19 & 20 in ref.189 (pdf pp. 22, 23):

  • For the modulators and transmitter-keying units:
  • 10x RV12P2000, 1x RG12D60, 1x AZ12, 6x RV275, 4x RV335, 4x RG62, all made by Telefunken.
  • 1x STV100/25Z and 1x STV280/80 made by Stabilovolt.
  • For the measurement/monitoring equipment:
  • 3x RV12P2000, 6x LV1, 6x RG12D60, 1x RGN4004, 3x RV275, 2x RV335, 2x RG62, all made by Telefunken.
  • 4x STV150/15 and 1x STV280/80, made by Stabilovolt.

CONSTRUCTION


The walls of the building are made of brick. There are four windows of 1.2x1.2 m (4x4 ft), and a door. Whatever equipment was installed inside this building, it must have fitted through the door or a window. Floor-to-ceiling height inside the building is about 3 m (10 ft), so the floor is well below the base of the concrete ring. This is why there is a small trench and steps that lead down to the door.

The three diagrams below show the cross-section (with measured dimensions) of the concrete ring and round building of the "Bernhard" installation at Aidlingen/Venusberg, Arcachon, and Hundborg:

Berhard station

Fig. 154: Cross-section of the installation at Aidlingen/Venusberg

(based on the measurements that I took in June of 2012)

Bernhard station

Fig. 155: Cross-section of the installation at Arcachon

(based on the measurements that I took in July of 2012)

Berhard station

Fig. 156: Cross-section of the Bernhard ring on Gåsbjerg hill at Hundborg

(based on ref. 115)

The concrete roof of the round building is supported by four columns, made of massive steel I-beams (H-beams, D: "Doppel T Träger"): the flanges are 30 cm (1 ft) wide and 24 mm (1") thick! The web of the beams is 32 cm (12½ inch) wide and 15 mm (0.6 inch) thick. So these columns have a cross-section of 30x37 cm. The columns are spaced evenly in the round wall. The roof-joists are made of the same heavy I-beams. Why would such a solid, heavy construction be necessary? The rotating superstructure weighed 120 metric tons (265 thousand lbs). Assuming the weight was distributed evenly between the four locomotives and the central support, the roof had to carry 120 / 5 = 24 metric tons (53 thousand lbs) statically!

The following diagrams show more details of the steel structure:

  • 4 large steel I-beam columns, with end-plates. The flange of these vertical I-beams is 30 cm (1 ft) wide, and the height of the beams is 37 cm (1 ft 3")
  • 4 large steel I-beam joists, with a joist-to-column brace and a triangular filler plate. The brace is a heavy steel plate (3 cm thick), as wide as the flanges of the columns and the joists. The joist and brace are mounted to the column with 8 bolts. The brace prevents the structure from racking ( = sideways swaying of the tops of the columns). The brace is mounted to the column at a 50° angle.
  • 4 steel doubler-plates, to better transfer vertical forces on the joist to the column, and to distribute any bending force to both flanges of the columns. The doubler-plate is mounted onto the end-plate of the column with 8 bolts, and to the joist with eight bolts.
  • 2 identical steel octagonal plates, to interconnect the four joists. Each joist is mounted to the two octagonal plates with 6 bolts. The plates have hole at the center.
  • 4 small steel plates that form the sides of a box that is placed between the octagonal plates. The corners of the box are butted up against the web of the joists, but do not appear to be welded to them. The function of the box is unclear - possibly to prevent the center of the top octagonal plate from being pushed down, possibly they where used to pre-assemble the two octagonal plates.
  • 4 small steel I-beams, connecting the joists above the braces. This makes the structure torsionally stiff. I found no sign that the columns are interconnected at the bottom.
  • Numerous steel concrete reinforcement rods/bars ("rebar"), placed radially inside the concrete of the roof. The ends of the rods are curled back.

Berhard station

Fig. 157: The major elements of the steel support structure of the round building

(based on my measurements of the "Bernhard" at Aidlingen/Venusberg)


Berhard station

Fig. 158: Dimensions of the steel "skeleton" of the round building

(based on my measurements of the "Bernhard" at Aidlingen/Venusberg)

A doubler-plate reinforces the joint of each joist and the associated column:

Berhard station

Fig. 159: Dimensions of the column-to-joist doubler plate

(based on my measurements of the "Bernhard" at Aidlingen/Venusberg)

Berhard station

Fig. 160: Details of the steel support structure of the "Bernhard" at Aidlingen/Venusberg


Two heavy octagonal plates interconnect the four large I-beams joists at the center of the roof. One plate on top, one from below. There are two brackets on the bottom plate, for suspending equipment. The space between the brackets is about 55 cm (22 inch).

Berhard station

Fig. 161: The octagonal mounting plate against the ceiling - with mounting brackets to suspend equipment


Berhard station

Fig 162: Dimensions of the octagonal mounting plates and associated brackets

(based on my measurements of the "Bernhard" at Aidlingen/Venusberg)

Four smaller I-beams make the top of the structure torsionally stiffer, by bracing the four main joists:

Berhard station

Fig. 163: Top view of the steel support structure

(based on my measurements of the "Bernhard" at Aidlingen/Venusberg)

The next photo shows the remains of the steel structure (upside down), after removing the walls and collapsing the roof:

Berhard station

Fig. 164: The remains of the steel structure at Nevid, after destruction of the building in 2015

(source: © jdvlavicka)

Berhard station

Fig. 165: The remains of the steel structure at Nevid, after destruction of the building in 2015

(source: © jdvlavicka)

A very large ball bearing was installed in the middle of the roof:

Berhard station

Fig. 166: The round building with the raceway of a large ball bearing in the middle of the roof

(Be-12 at Nevid/Plzeň; source: © Jacek Durych, used with permission)

It had an outer diameter of about 40 cm (≈16 inch). The ball bearing held a cylindrical tube, that rotated with the antenna system and the cabin. The bottom of this tube has a flange, for connecting to equipment that rotated with the tube. The tube had a diameter of about 14 cm (5½ inch).

Berhard station

Fig. 167: Tubular shaft descending through the roof of Be-6 at Marlemont and Be-10 at Hundborg

(source Hundborg photo: www.gyges.dk, used with permission; note the original wiring)

A small turntable is installed on top of the ball bearing, and the tube is attached to it from below:

Berhard station

Fig. 168: small turntable on top of the shaft

(Be-6 at Marlemont; note the large mounting bolts inserted into the turntable from below)


SUPPLY OF ELECTRICAL POWER

The "Bernhard" installation had several consumers of electrical power:

  • Four electric locomotives. Reportedly one of the motor types was a low-rpm model, rated 10 kW (ref. 99). Let's assume all eight locomotive motors (two types of DC motor and one synchronous AC motor) had this rating. This would add up to 80 kW in total.
  • Two model AS 4 transmitters, each with an output power of 500 watt, or 1 kW total. Each AS 4 had a power supply model NA 500, with separate inputs for 220 and 380 volt 50 Hz 3-phase AC ("Drehstrom"), rated at 5 kVA. Ref 143 (p. 7) states that each NA 500 was normally powered by a standard heavy motor-generator model "A" ("schwerer Maschinensatz A"), rated at 12 kVA (see Fig. 163 below), or the public power grid. Either way, the power source was loaded with 5 kW. I.e., ten times the transmitter output power, and 10 kW total for the two transmitters combined.
  • Miscellaneous items in the equipment room (three modulators, two printers, three projector lights in the optical disk assembly) - let's conservatively assume 1 kW.
  • Heating and lighting in the rotating cabin and equipment room below it, as well as in the ancillary building) - let's assume 4 kW.

Adding up the four types of electrical loads, we arrive at an estimated total load of 80 + 10 + 5 = 85 kW. To translate this to the required power from an AC source, we have to assume a worst-case phase angle φ between the generated voltage and current. For a reasonable cos(φ) = 0.8, the AC-power source would have to be dimensioned for at least 85 / 0.8 ≈ 106 kVA.

The table below shows the specified power supply for a number of Wehrmacht transmitters of the same era, including other beacon transmitters. The power supply outputs are all dimensioned for at least four times the transmitter output power.

Berhard station

Fig. 169: Specified power supply rating for a number of Wehrmacht transmitters

(based on various data sheets)

To be able to operate independently from the local public power grid, the "Bernhard" installation had its own local power generator, driven by a combustion engine (diesel or gasoline/petrol). Ref. 183 (pdf p. 18) states that "Bernhard" backup generator was powered by a diesel engine ("Notstrom-Diesel"). Ref. 180 implies that "Bernhard" station Be-0 near Trebbin had a 120 kVA backup diesel generator. Note that this station was also a test site, and probably had more ancillary buildings (labs, offices, kitchen, living quarters) than a standard "Bernhard" station.

Based on the local situation (access to the local public power grid), the "Bernhard" installation typically included a high-voltage bunker ("Hochspannungsbunker"), e.g., ref. 99. It contained one or more transformers, to connect to the multi-phase regional Hochspannungsnetz (high voltage public power grid, 110-220 kV in Germany), or to the local Mittelspannungsnetz (6-60 kV, typically 10 or 20 kV). The local Niederspannungsnetz (several km) carried less than 1 kV. Incidentally, towards the end of the war, the minimum frequency of the 50 Hz power grid was reduced to 43.3 Hz in the Central German block, and 41 Hz in the Western German block. Ref. 14.

Berhard station

Fig. 170: The two sources of electrical power of the "Bernhard" installation


The next table lists the horse power (HP) of the engine of a number of Wehrmacht electrical power generators ("Maschinensätze") for transmitters, various models of Flak-Scheinwerfer (search-lights for Anti Aircraft gun installations; ref. 152A, 152B) and even of a field bakery. This ranges roughly from 1.5 - 3 HP/kVA. Assuming a 120 kVA generator, this implies an engine with 180 - 360 HP. The specification of the actual "Bernhard" generator and associated engine is unknown.

Berhard station

Fig. 171: Engine power for a number of Wehrmacht generators


The photo below shows the 110 kVA emergency backup generator of the "Goliath" Kriegsmarine transmitter station for world-wide communication to submerged submarines (incl. via Hellschreiber). It has a 150 HP diesel engine, ref. 218 (p. 188). That is, 1.4 HP/kVA. Note that the main generator, for the 1 megawatt (!) "Goliath" transmitter, had a power of 1800 kVA and was driven by a 2110 HP diesel engine! That is, about 1.2 kVA/HP.

Berhard station

Fig. 172: Example of a 110 kVA, 3-phase 380 VAC diesel generator

(source: "Der Goliath in Bildern - Fotos vor 1946/47" web page)

Ref. 103 suggests that the generator(s) of the "Bernhard" station Be-14 at Aidlingen/Venusberg were powered by two engines that came from high-speed patrol boats of the French navy. However, the French navy's "vedette rapide" boats were standard British-built "Fairmile" models. The smallest model had two Hall-Scott Defender V12 gasoline (UK: petrol) engines of 650 BHP each. The larger "A" model had three 600 HP engines. Clearly a single engine would have been able to supply more power than needed for a Bernhard installation, even if power was also generated for the local FLAK unit and its search-light(s). On the other hand, this Be-14 station was built towards the end of the war, when materials other than rocks and stone were in increasingly short supply. A strong engine that costs nothing, is better than a correctly sized engine that is not available... There are two stone buildings near the ring of Be-14. In the middle of one of them, there is a rectangular concrete slab that measures 1.4 x 3.25 meters (4.6x10.7 ft). The slab has 6 pairs of shallow round dimples, 8 and 10 cm in diameter. The purpose of the slab in unknown. Possibly the dimples corresponded to mounting feet of a motor-generator, such as shown in the photo above.

Berhard station

Fig. 173: A concrete slab in the middle of an ancillary building of Be-13 at Aidlingen/Venusberg


Below one of the windows of the round building of the "Bernhard" at Arcachon, there is an old 4-prong junction box with triangular shape. Near this box, several old cables enter the building through the wall, just above floor level. This appears to be where 3-phase AC-power entered from the generator in a nearby building.

Berhard station

Fig. 174: Large 4-prong (3-phase) junction box on inside wall of the round building of Be-7 at Arcachon


PATENTS

Below is a listing of patents related to the "Bernhard" system.

Patent number Patent office Year Inventor(s) Patent owner(s) Title (original) Title (translated)
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
692583 RP 1937 H. Gross Conz Elektricitäts G.m.b.H. Frequenzwandlergruppe zur Erzeugung konstanter Mittelfrequenz Frequency converter for generation of constant mid-frequency
737102 RP 1935 W. Runge, L. Krügel, F. Grammelsdorff 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 geometric direction of a directional beam [A/N & E/T beacons, via monitoring receiver]
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 A. Lohmann Telefunken G. für drahtlose Telegraphie m.b.H. Verfahren zur Richtungsbestimmung mittels rotierender Richtstrahlung Method for direction-finding with a rotating directional beam
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 1939 A. Lohmann Telefunken GmbH Einrichtung zur Speisung eines rotierenden Richtantennensystems Device for capacitive coupling of a transmitter to a rotating directional antenna system
767528 RP 1938 A. Lohmann Telefunken GmbH Verfahren zur Richtungsbestimmung Method for direction-finding
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
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
767937 RP 1939 A. Lohmann Telefunken GmbH Einrichtung zur Durchführung eines Verfahrens zur Richtungsbestimmung Device for implementation of a method for direction finding

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 scale info via Nipkow-video]
620828 RP 1933 - Marconi's Wireless Telegraph Co. Ltd. Funkpeilverfahren Method for direction finding [transmission of compass scale 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

  • The purpose of FuSAn725, with 4 or 5 kW transmitters instead of 0.5 kW? Range increase, interference-proofness?
  • Open-wire feedline between the dipoles: characteristic impedance (spacing between the wires, wire diameter)?
  • Were the rails continuously welded rail or jointed?
  • Purpose/content of the four corner-sheds? Dead-weight?
  • Purpose of two different types of DC motors per locomotive?
  • Were both bogies of each locomotive motor-driven, and one or both axes of each driven bogie?
  • Which company was the manufacturer of the locomotives?
  • Purpose of dimples in the top of several of the concrete rings, between the rail ties/shoes?
  • Purpose of a box with 5 kg of graphite (powder?) that was part of the standard equipment (sheet 20, ref. 189)?
  • Why was a special Telefunken crystal module needed in the AS 4 transmitters (improve the frequency accuracy/stability?).
  • Purpose of the remote tachometer in Locomotive nr. 4 (going to the rotating cabin), in addition to the tachometer track of the optical disk (in the round equipment building below the rotating cabin)?
  • Frequency of the accurately regulated 3-phase AC (50 Hz?), and the number of rotor poles of the synchronous AC motor of locomotive nr. 4?


REFERENCES


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.

External links last checked: October 2015 unless noted otherwise.


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