- [FuG120 overview]
- ["Bernhardine" Hellschreiber printer]
- [Printer-channel for signal-strength]
- [Printer-channel for azimuth]
- [Printer model HS120]
- [Printer model Psch120]
- [Printer model Psch120A]
- [Printer model Psch120k]
- [Printer-amplifier SV120]
- [SV120 pulse-width modulator]
- [Filter-unit SG120]
- [Switching-unit UG120]
- [Power-supply U120]
- [Aircraft equipped with FuG120]
- [FuBl radio-navigation receiver]
- ["Bernhardine" for FuG139 "Barbarossa" & FuG126 "Baldur/Bord"]
- [Unknown/unclear aspects]
Last page update: 15 April 2017
- ["Bernhard/Bernhardine" Luftwaffe radio-navigation system]
- [FuSAn 724/725 "Bernhard" ground station]
- ["Bernhard" station locations]
The FuG 120 "Bernhardine" printer system is the airborne counterpart of the FuSAn 724/725 "Bernhard" radio-navigation beacon of the Luftwaffe, 1941-45. It uses the standard on-board EBL3 VHF receiver that was already used with beacon systems during "blind" approach and landing, and in combination with other beacon systems for guiding bombers and fighter aircraft to their target. The printer system provides the operator with the bearing from the selected "Bernhard" ground station, and could also receive short "Reportage" text messages with information about enemy aircraft. The official German designation says it all: the FuG 120 is a "UKW-Richtstrahl-Drehfunkfeuer-Empfangszusatz mit Kommandoübertragung". That is, a VHF directional rotating-beam receiver-accessory with command data-link.
Fig. 1: "Bernhardine" airborne Hellschreiber printer of the "Bernhard/Bernhardine" radio-navigation system
(click here for a full size image)
For many years, I have searched for original German documents on the FuG 120 system. Finally, in December of 2013, I located a US microfilm copy in the National Library of... Japan! Several weeks later, a photo copy of the 40+ page document arrived in the mail, see ref. 15. It confirmed most of my assumptions and conjectures, and clarified some open questions.
The FuG 120 "Bernhardine" system comprises the following equipment items (ref. 4, 5, 15, 42, 43, 44, 85B/C/D):
- SV 120 printer amplifier unit ("Schreibverstärker"),
- SG 120 audio filter unit ("Siebgerät", "Schreibgabelschaltung"),
- UG 120 switching unit ("Umschaltgerät"),
- SpKf 1a mode switch ("Sprechknopf"), system mode-switch (landing beacon vs. "Bernhard" navigation-beacon); modified PPT-switch ("push to talk")
- U 120 power supply unit ("Umformer"),
- HS120 dual-trace Hellschreiber printer ("Hell-Schreiber") or Psch 120 ("Peilschreiber" = bearing-printer, also a Hellschreiber).
Table-1: manufacturers of the HS 120 (Dr.Ing. Hell company) and Psch 120 (Siemens & Halske LGW)
(source: ref. 44)
According to ref. 44 (p. 188), most of these equipment items date back to 1941, with the exception of SpKf1a (1942), Psch 120 (1942), and SV 120 (1944). However, ref. 3 suggests that series production did not start until 1943, and also states that the first "Bernhard" ground stations were built in 1942.
Fig. 2: Test rack with FuBl 2 navigation receiver system (left) and rack with FuG 120 "Bernhardine"
(source: p. 99 in ref. 3)
Of course, the aircraft installation included a number of mounting and interconnect items (besides cables):
- RDFS 120, Rahmen für Drehfunkschreiber: mounting frame for rotating-beacon printer,
- UF 120, Umformerfußplatte: mounting plate for power converter U 120,
- RSV 120, Rahmen für Schreibverstärker: mounting frame for printer amplifier SV 120,
- SGF 120, Siebgerät-Fußplatte: mounting plate for filter unit SG 120,
- VD 120, Verteilerdose: junction box,
- ZLK VIII S 3, Zwischenleitungskupplung: splitter/coupler unit.
The equipment items UG120, SV120, U120, as well as the installation items RDFS 120, UF120, SGF 120, RSV 120, and VD 120, were all manufactured by a Telefunken plant in Berlin-Zehlendorf (same part of Berlin as the Hell company) or in Erfurt. The associated 3-letter military manufacturer code is "bou". The SG 120 filter unit was manufactured by Siemens Luftfahrtgerätewerk (LGW) Hakenfelde GmbH, manufacturer code "eas". The SpKf1a mode-switch and the ZLK VIII S 3 coupler-unit were made by "Frieseke & Höpfner, Spezialwerke für Flugfunktechnik" in Berlin Potsdam-Babelsberg and in Breslau. Their manufacturer code was "gqd" (p. 188 in ref. 51).
The total weight of the FuG 120 units (incl. mounting frames) is about 38 kg (84 lbs).
In addition to the on-board equipment, there was a number of ground-test equipment items (ref. 15, 44, 45), mostly built by Telefunken (p. 188 in ref. 44):
- TOG 120, Tongenerator: an audio signal generator,
- PV 120 and PV 64, Prüfvoltmeter,
- PschMG 120, Peilschreibmeßgerät, a tester for the Hellschreiber printer,
- PS 120, Prüfsender: transmitter to test the complete functionality of the FuBL2 plus FuG120. This implies a "Bernhard" beacon simulator,
- PGst 120, Prüfgestell, a test rack (possibly such as shown in Figure 2 above).
The airborne "Bernhardine" system with its Hellschreiber printer, works together with a "Bernhard" beacon ground-station. The "Bernhard" beacon has a rotating antenna system that makes one revolution every 30 sec:
- One antenna array (purple in Figure 3) has a radiation pattern with two narrow lobes. There is a steep null between the lobes. This antenna transmits a constant 1800 Hz tone signal.
- The radiation pattern of the second antenna array has a single lobe (green in Figure 3). Its maximum coincides with the null of the twin-lobe beam. This antenna continuously transmits the direction in which the antenna is pointing (azimuth, bearing from the beacon) in Hellschreiber format, with 2600 Hz tone pulses. However, this transmitter operates at a frequency that is 10 kHz higher than that of the constant-tone transmitter.
Fig. 3: Concept of the Bernhard/Bernhardine radio-navigation system
The "Bernhardine" Hellschreiber-printer in the aircraft prints two parallel tracks on a paper tape, see Figure 3 above:
- The lower track prints the azimuth value of the single-beam signal, as the rotating beam illuminates the aircraft for several seconds during each revolution of the antenna system. This is a two-digit value for every ten degrees of azimuth (as is done to identify the magnetic heading of runways at aerodromes).There is also a tick mark for each degree. A station-identifier letter is printed every 10 degrees ("M" in Figure 3).
- The upper track prints the (clipped) signal strength of the received continuous signal of the twin-beam antenna. Hence, the printed pattern shows the two lobes of that twin-beam, with the sharp null in between. This accurate V-shaped null points at the exact azimuth value that is printed in the lower track (255.0° in Figure 3).
To the best of my knowledge, no original "Bernhard" audio recordings exist. So I have simulated the sound of a transmission. The recording below comprises two beam-passages: once without the information in Hellschreiber-format (i.e., only the constant 1800 Hz tone), and once the constant tone plus the constant stream of 2600 Hz Hellschreiber-pulses. The beam-passage duration is about 3½ seconds, consistent with the print-out shown in Figure 15 below.
Simulated sound of two "Bernhard" beam-passages - without & with Hellschreiber tone pulses
During 1942-44, RAF 192 Squadron (§9.3 in ref. 175) and the British/American Noise Investigation Bureau (ref. 173A-173E) investigated the Hellschreiber signals that were transmitted by "Bernhard" beacons. The British Foreign Office Wireless Intercept station (WI-station = Y-Station) at Knockholt (near Sevenoaks, in the countryside, about 30 km southeast of the City of London) assisted 192 Sq with knowledge about the Hellschreiber system, its reception, and the required tone-filter.
"BERNHARDINE" HELLSCHREIBER PRINTER
A standard Hellschreiber printer consists of an inked spindle that is placed across, and slightly above, a moving paper tape. Below the paper tape is an electromagnet with a hammer. See Figure 4A. When the magnet is energized, the hammer pushes the paper tape against the continuously turning spindle. The magnet-solenoid is energized as soon as, and as long as, a tone signal is received. This causes a dot or line segment to be printed across the paper tape. The length of the printed line depends on the amount of time that the electromagnet is energized.
Fig. 4A: Principle of a standard Hellschreiber printer
Unlike very complex (and large) "telex" teleprinters, this very robust method requires only detection of "signal present / not present". It requires no machine-interpretation of a sequence of "bits", to determine what to print. Also, the compact Hell-printer mechanism has very few moving parts, and is not limited to printing a predetermined character-set. The Hellschreiber can be thought of as a remote dot-matrix printer for any form of low-resolution graphical information (a line of text or other symbols). See the Hellschreiber "How it works" page.
The "Bernhardine" system is actually a dual Hellschreiber-printer. It has two independent printer mechanisms. The lower trace prints the compass rose (azimuth) or command text-messages. This is transmitted in Hell-format by the single-beam antenna array of the rotating "Bernhard" ground station. The upper trace prints the strength of the continuous tone transmitted by the twin-beam antenna array of the ground-station. The two printer-spindles are mounted on the same motorized shaft that turns at 720 rpm (12 rps, ref. 15).
Fig. 4B: Principle of the dual-trace "Bernhardine" Hellschreiber printer
The "Bernhard" beacon rotates twice per minute. So it has a rotational speed of 360° / 30 = 12° per second, or 1° in 1/12 sec. The azimuth data is printed with a resolution of three pixel-columns per degree (see Figure 5). That is: 3 x 12 = 36 columns per second. The bar-graph is printed with six pixel-columns per degree (ref. 15). That is: 6 x 12 = 72 columns per second.
Fig. 5: Azimuth print-out
(source: ref. 15)
Of course it is possible to print 36 pixel columns per second, with a spindle that has a single thread that is wrapped once around the hub of the spindle. Such a spindle would have to turn at 36 rps = 2160 rpm. Likewise, such a spindle can print 72 bar-graph columns per second, by spinning at 72 rps = 4320 rpm. This is not practical for two reasons. First, 4320 rpm is extremely fast. And to get a stable speed, the motor (with down-gearing) would have to run even faster. Secondly, in the "Bernhardine" printer, both spindles are mounted on the same shaft, so they turn at the same speed. The solution is simple: use multi-start spindles. By using a spindle with N starts, the required shaft speed is reduced by a factor N. Two spindles on the same shaft can have a different number of starts.
In the "Bernhardine", the bar-graph printer has a 6-start spindle (N = 6): it has six thread-segments. Each covers 360° / 6 = 60° of the circumference of the spindle hub. The thread segments do not overlap. See Figure 6. The azimuth printer has a 3-start spindle: N = 3. Its three thread-segments each cover 360° / 3 = 120° of the spindle hub. This means that these two spindles can turn at the same speed: 2160 / 3 = 4320 / 6 = 720 rpm. This speed is easily obtained with down-gearing a standard 3000 - 4000 rpm motor. E.g., the "Presse Hell" printer has a 3000 rpm motor, the "Feld-Hell" machine has a 3600 rpm motor. The 3-start spindle prints three columns per rev, the 6-start spindle prints twice as many.
Fig. 6A: The 6-start spindle (bar-graph) and 3-start spindle (azimuth) of the "Bernhardine" Hellschreiber printers
Fig. 6B: The 6-start spindle of an HS120 "Bernhardine" Hellschreiber printer
The columns of the bar-graph have to be printed bottom-to-top. In principle, the azimuth data could be printed either bottom-to-top or top-to-bottom. However, as explained below, it has to be printed top-to-bottom, because the printer is synchronized to the degree tick-marks at the top of the printout (every third column = 1 rev of the spindle). This means that the two spindles have to print columns in opposite direction, even though they turn in the same direction! This is solved by one spindle having a right-hand thread, and the other spindle a left-hand thread. See Figure 6A above.
The color of the printer ink is reported as being red (§29 in ref. 6). However, this would have resulted in poor contrast on the white paper tape, compared to using dark ink, such as the Hell standard dark violet. Also, red was probably not compatible with night-time lighting conditions in a cockpit (often yellowish, or even red, as this color light does not affect night vision). Per ref. 15, "the usual ink of type HB-50" was to be used. This is Haberolin-Basolomin ink. Haberolin was a deep-black cloth dye (marking-ink), made by Wilhelm Haber. "Wilhelm Haber Stempfelfarben" company was founded in 1873. The company still exists today (located in Lommatzsch, 160 km (100 mi) south of Berlin), under the name "Wilhelm Haber Stempelfarben Steffen Haeckel e.K." Dark violet "HB 45" was the standard ink for other Hellschreibers, such as the Feldfernschreiber. I do not know the color of HB50.
The dual Hellschreiber-printer of the "Bernhardine" system comprises the following elements, see Figure 7:
- 24 VDC motor,
- electro-magnet (printer-solenoid) for the bar-graph printer,
- electro-magnet (printer-solenoid) for the azimuth printer,
- electro-magnet (solenoid) for the synchronization mechanism of the azimuth printer
- six-notch cam wheel on the shaft of the printer spindles. This part of the pulse-width modulator circuitry of the azimuth printer,
- potmeter for the manual gain control of the pre-amplifier in the SV120 printer-amplifier,
- push-button to reset the Automatic Gain Control (AGC) circuitry in the SV120 printer-amplifier, for the EBL 3 radio receiver,
- "dimm/bright" toggle switch for the brightness of the lighting for the print-out.
Fig. 7: principle diagram of the HS 120 dual Hellschreiber printer
HELLSCHREIBER PRINTER-CHANNEL FOR SIGNAL-STRENGTH
As described above, the "Bernhard" ground station transmits a constant tone via its twin-lobe antenna array. The signal strength of the received signal is printed as a bar-graph in the upper trace of the paper tape. See Figures 3, 8, and 9. The bar-graph has six bars per degree of azimuth (ref. 15). Special circuitry is used, to ensure that the bars start exactly at the bottom of each printed pixel column, and that the height ( = duration of the energization of the printer magnet) corresponds to the signal strength (0 - 100%).
Fig. 8: signal strength bars, as printed with the Bernhardine-Hellschreiber
(source: ref. 3)
Fig. 9: Signal-level bar-graph based on received signal strength from the main lobes of the antenna pattern
(source: adapted from ref. 46)
HELLSCHREIBER PRINTER-CHANNEL FOR AZIMUTH (BEARING FROM THE GROUND-STATION)
The single-lobe antenna of the "Bernhard" ground-station continuously transmits the momentary direction of the antenna (i.e., antenna azimuth = bearing from the station) in Hellschreiber-format. This is printed by the second Hellschreiber-printer of the "Bernhardine", directly below the bar graph of the signal-strength. The result is a segment of a compass rose that is about 30-40 degree wide. The V-shaped dip in the bar graph points at the actual bearing-from-the-beacon that the aircraft is on (255.0° in Figure 10B).
Fig. 10A: Remote compass, as used e.g. in Fw190
(made by A. Patin & Co. G.m.b.H. of Berlin)
Fig. 10B: the compass rose segment is printed below the bar graph
The motor in the "Bernhardine" Hell-printer is not synchronized to the rotation of the optical disk of the "Bernhard" ground station, that sends the azimuth data in the form of a pixel stream in Hellschreiber-format. In a standard Hellschreiber system, speed differences between sender and printer result in slanting of the printed track. E.g., upward slanting if the printer is faster than the transmitter:
Fig. 11A: Upward slant for receiver spindle that is faster than the transmitter
Even if sender and printer are running at exactly the same speed, phase differences result in the printed track being shifted up or down. The slant, or shift, causes part of the track to end up beyond the vertical limit (upper or lower) of the track. See Figure 11B.
Fig. 11B: The printed text is split, due to phase difference between sending and receiving motor
(motor speeds are identical - printed text line is not slanted)
In standard Hellschreiber printers of the 1930s and 1940s, the classical solution to this problem is to use a printer spindle with a thread that is wound twice around the hub of the spindle. Such a spindle prints two identical text lines in parallel, one above the other. Hence, at least one text line is always fully legible. See Figure 11C. This is combined with manual adjustment of the printer's motor speed.
Fig. 11C Double-line text remains completely legible despite slant and shift, caused by speed & phase difference
This solution is not an option for the "Bernhardine" printer. Yes, doubling the printout of the azimuth data would make that data legible at all time. However, due to the slant or vertical shift of the printed azimuth data, the bar-graph pointer may no longer line up with the degree tick-marks. See Figure 12. Furthermore, manual speed adjustment would not have been practical for the "Bernhardine", as the rotating beacon is only received about 3-5 sec per 30 sec rotation, and (night) fighter pilots cannot afford to spend significant time on such a task. The azimuth printer must somehow be synchronized to the pixel stream, such that the degree tick-marks are aligned with the top of the printed track. I.e., they must all be printed just below, and parallel to the bar-graph.
Fig. 12 The standard Hellschreiber "double helix" is not an option for the "Bernhardine"
Unlike "telex" teleprinters and post-war start-stop Hellschreibers, the Hellschreiber "font" of the azimuth data contains no explicit start "bits". However, the pixel stream does include a tick-mark at the top of every third pixel column. Each tick-mark is at least three pixels long (the 5° tick-marks are 4½ pixels long, and the 10° tick-marks 10 pixels). These tick-marks are used for synchronization.
As in all teleprinters with character synchronization, the "Bernhardine" motor runs a little faster than the nominal speed: 1.5% (ref. 15), equivalent to about ½ pixel per three columns. This way, it finishes printing each character (here: 3 pixel columns) slightly early. The printer then waits a brief moment, until the next sync pulse (here: tick-mark) is detected, and then starts to print the next character at exactly the right moment. The same method was used for many decades, to synchronize clocks at train stations to an accurate central master clock: each minute, all station clocks run several seconds fast. At the top of the minute, the hands of the clock are held in place, until the central clock sends a release-signal to all slave clocks, to start ticking away the next minute.
As stated above, the spindle of the bar-graph printer and the spindle of the azimuth printer are both mounted on the same spinning shaft. But only the azimuth spindle requires synchronization. This implies that this spindle is not permanently fixed to the spindle shaft! It is actually mounted onto that shaft with a small standard slip-clutch. This allows the spindle to be "grabbed" and stopped, while the spindle shaft keeps turning at a constant speed. As soon as the spindle is released, it starts to spin again with the shaft. So a "grab, hold, and release" mechanism is needed. This is just a simple so-called "indexing" mechanism. See Figure 13 below. There is a "catch" notch or pin on the spindle hub (not on the spindle shaft!). A small hook at the end of a spring-loaded lever holds the notch, and prevents the spindle from turning with the spindle shaft. When the motor is running, the clutch slips continuously. A brief energization of the synchronization electro-magnet causes the notch to be released. The spindle now turns with the shaft (no slip). After one revolution of the spindle, the notch on the spindle is caught again by the lever. The spindle is briefly stopped until the next release-pulse (= degree tick-mark), etc. The synchronization-magnet is placed in series with the magnet-solenoid of the azimuth printer. That is, they are energized and de-energized simultaneously.
Fig. 13: Synchronization mechanism of the azimuth Hell-printer
(source: adapted from Figure 9d of ref. 15)
Let's go through a complete "catch-and-release"" sequence, see Figure 14. Assume that the spindle is held by the sync-lever. The first pixel of a degree tick-mark is received. This causes the notch of the spindle to be released. The spindle turns freely for 1 revolution = three pixel columns. Note that, depending on the pixel pattern in these three columns, the sync-magnet may arm and disarm the lever several times during this revolution! However, this has no effect, since the notch on the spindle is only near the hook of the lever just before the spindle completes its revolution. The lever catches the notch during the white pixel that always precedes the next degree tick-mark ( = bottom of the preceding pixel column).
Fig. 14: Complete cycle of the synchronization process
This concept of synchronization is based on characteristics of the Hellschreiber pixel-stream instead of explicit start-bits. This was was re-used in the Hell Blattschreiber of the 1950s. In the standard Hell-system, the character font has two white pixels, both above and below each printed pixel column. I.e., there is symmetry in each pixel column, and there should be no black pixels at the top and bottom of the printed pixel columns. During printing, the actual vertical symmetry can be measured, and used to speed up or slow down the motor. This control-loop eliminates the phase difference and, hence, also the speed difference.
Hellschreibers developed after this Blattschreiber, all used start-stop synchronization with an explicit starts-pulse embedded into the first (normally blank) column of the character font: Hell-39/44, Hell 72/73, and Hell-80. The Hell-40 was a replacement for the "Presse Hell", so it did not use synchronization.
According to the "Bernhardine" manual (ref. 15), it required 2 to 4 beam-passages for the synchronization system to be tracking the tick-marks properly: "After selecting the beacon, wait until the Hellschreiber spools up and prints properly (1-2 minutes). The first two prints are not dependable". This could explain the wavy printout in Figure 15 (pink lines). The printed bar-graph is perfectly straight, as it is always fully synchronized to the spindle. Note that waviness could also have been caused by variations in the speed of the beacon.
Fig. 15: Print-outs with wavy azimuth track
(source: ref. 3)
As stated above, the AGC and synchronization circuitry of the SV120 printer amplifier provides automatic adjustment of the two printer tracks. The only manual adjustment available, is the gain control of the pre-amplifier of the SV 120. The knob (labeled "Empfindlichkeit" = sensitivity) is on the front of the HS 120 printer. Figure 16 shows how it had to be used to obtain correct printing quality.
Fig. 16: Incorrect and correct printing - adjustment with manual gain control on the HS120 printer
(source: figure 25 in ref. 15, ref. 48)
As stated above, the motor of the Hellschreiber printer ran 1.5% faster than the nominal speed of the beacon's azimuth data transmission. Note that this is more than the typical 0.5% speed difference between the transmitter and printer motors of "telex" teleprinters of the era. It basically implies that the "Bernhard" beacon should not turn faster than the nominal 12°/sec rotational speed. The beacon should also not turn more than 1.5% slower than the nominal speed. If so, a black pixel at the bottom of the column preceding the next tick-mark (e.g., the last pixel of the beacon identifier letter), could inadvertently be interpreted as the next tick-mark and release the spindle. This may cause slant to continue or even worsen, until the printer temporarily syncs again to a real tick-mark. Note that at least two out of every five degree tick-marks are preceded by least one complete white pixel column. This is enough for a "clean" sync.
A few "Bernhard" stations had the capability to transmit 10-character "Reportage" messages, instead of the the azimuth data. Clearly, these messages should also be printed as a single horizontal line of text. I.e., without slant or vertical shift. The normal Hellschreiber font does not include a tick-mark at the top of every third pixel column. The character generator that was used for sending the "reportage" text strings must, however, have included such extra pixels. This would not have been difficult to implement, and would not have been very distracting in the print-outs.
"BERNHARDINE" PRINTER MODEL "HS 120"
I have documented three HS 120 machines: one in the collection of the Imperial War Museums (catalog nr. COM 493, Werk-Nr. 70206), and two in private collections (one with Werk-Nr. 70346, the other one without equipment label).
The HS 120 unit measures 35.7x15x14 cm without the housing (WxHxD, ≈14x6x5½"). This is actually quite compact, and not the unrealistic 60x30x20 cm (≈23½x12x8") that is often quoted for this model (ref. 6, 49). The official manual (ref. 15) states the following dimensions: 36.2x21x17.4 cm (WxHxD, ≈14.3x8.3x7"). However, the latter height includes a large connector that protrudes from the bottom of the unit, and mounting lugs at the top and bottom on the back of the housing (see Figure 13 in ref. 15 and Fig. 19-21 below). The unit weighs 7 kg (15½ lbs). Based on its size and the fact that it required attention, it was only used in larger aircraft (two or more seats, e.g., near the radio/radar operator), and in the Bernhard ground monitoring station.
Fig. 17: Front view of an HS120 Hellschreiber - protective cover down
(printer with Werk-Nr. 70206; photo used in accordance with ref. 169)
Fig. 18: Front view of an HS120 Hellschreiber - protective cover up
(printer with Werk-Nr. 70206; photo used in accordance with ref. 169)
The window in front of the paper tape measures about 24x4 cm. The paper tape has about three times the width of standard Hellschreiber tape (15 mm). The tape moves from right to left in the window. The paper tape is re-wound onto a second reel inside the printer, so there is no paper tape mess in the cockpit. The upper part of the front panel is hinged, to facilitate inserting the paper tape across the front of the printer.
The front panel has controls for printer-amplifier gain ("Empfindlichkeit" = sensitivity) and lighting brightness ("dunkel/hell" = dim/bright). The push button ("Drucktaste") marked "D" is connected to the SV120 printer-amplifier. It is used for resetting the automatic gain control signal to the EBl 3 radio receiver. At the left and right bottom corner, there is a large mounting bolt that goes all the way through the unit, into the equipment rack of the aircraft. The red ring around the hole for the bolts indicates that the bolts may be removed for field maintenance by standard technicians. The bolts are spring-loaded, to expedite removal and installation of the unit.
There is a 20-pin connector on the bottom of the unit:
Fig. 19: Bottom view of an HS120 Hellschreiber
(printer with Werk-Nr. 70206; photo used in accordance with ref. 169)
The connector carries the markings "126-853-U01" and "Fl 32113-6" (ref. 170), as well as the triangular "List" logo. It was made by the company "Elektro-Mechanik Heinrich List" in Berlin-Teltow. One of the production sites of the Hell company was located in the same industrial park. The List company had two military identifiers ("Fertigungskennzeichen") for its Berlin facilities: "hbu" and "ocw". After WW2, the Teltow area became part of the Soviet Occupation Zone. In 1945/46, the confiscated Hell and List companies in Teltow were combined into the "Elektro-Feinbau GmbH", and by 1948 absorbed into the people-owned "VEB Mechanik-Askania Teltow" company, to be renamed "VEB Geräte- und Regler Werke Teltow" in the early 1950s. Ref. 171.
Fig. 20: The 20-pin connector on the bottom of the HS120 Hellschreiber (retaining clip missing)
(printer with Werk-Nr. 70206; photo used in accordance with ref. 169)
Fig. 21: Main building (left) and production buildings of the List company (1945)
(source: ref. 170)
There are two vertical strips on the back of the unit, with lugs for bolting the unit onto an equipment frame in the aircraft:
Fig. 22: Rear view of an HS120 Hellschreiber (upside down)
(printer with Werk-Nr. 70206; photo used in accordance with ref. 169)
There is an equipment label on the front of the unit:
Fig. 23: Label on the front panel of the HS120 Hellschreiber
(printer with Werk-Nr. 70206; photo used in accordance with ref. 169)
The label in the photo above provides the following information:
- Gerät-Nr. 124-1425A-1
- Werk-Nr. 70206
- Anforderzeichen: Ln 28990
"Gerät-Nummer" 124-1425A-1 refers to a "Spezial Hellschreiber". All items of the FuG 120 "Bernhardine" system have a Gerät-Nummer starting with "124". This two-part Luftwaffe numbering system is similar to the one used by the Heer (Army), ref. 50: a category number ("Stoffgliederungsgruppe", possibly with a suffix for an "Untergruppe" sub-category), followed by an item number.
"Werk-Nr." is a production number. Obviously, no 70206 units were ever built. The "7" may refer to the production series or batch, model variant, modification standard, or factory. The "0206" would then be the actual serial number of this particular unit.
"Anforderzeichen" Ln 28990 (p. 28 in ref. 44). The "Ln" number refers to a Kennblatt (specification sheet) of the Luftwaffe Luftnachrichten (Signal Corps), ref. 52. The major items of the FuG 120 span the Ln-number range 28980-28990 (see pp. 7, 8, 26 in ref. 15). This particular Ln-number belonged to the technical domain of LU-F-NAVKOMMÜB: Aeronautical Radio Navigation, Communication, Surveillance. These days, the combination Com-Nav-Surveillance ("CNS") is still used in aviation! The HS120 was built by the Hell company, starting in 1942 (p. 188 in ref. 44).
The next photo shows three very faded stamps near the equipment label (the photo was processed to enhance the markings):
- HS 120, the equipment designator.
- "cmw" - this is the 3-letter military manufacturer code ("Fertigungskennzeichen") of the Hell company.
- Waffenamt acceptance stamp "BAL 599" inside a circle.
Fig. 24: Markings stamped on the front panel of the HS120 Hellschreiber
(printer with Werk-Nr. 70206; photo used in accordance with ref. 169)
According to Luftwaffe service regulations, "BAL" stands for Bauaufsichten des Reichsluftfahrtministerium (the Administration of the RLM for the Supervision of Construction, ref. 52, 53), in short "Bauaufsicht Luft". It was subordinate to the Technisches Amt of the RLM. The number "599" refers to an accredited inspector.
The HS 120 with Werk-Nr. 70346 does not have this large "BAL 599" stamp. Instead, it has a white stamp: "BAL 378" inside an octagon. The same stamp appears inside the unit, on the chassis near the motor:
Fig. 25: "BAL 378" acceptance stamp near the equipment label and next to the motor
(left: printer with Werk-Nr. 70346; right: printer without Werk-Nr. but Nr. 70346 has same stamps)
This BAL number has also appeared on products of "Fernmeldetechnisches Entwicklungslaboratorium Dr. Ing. H. Kimmel" ("Development lab for telecom equipment", though they also made measurement equipment) in Munich. Their 3-letter military manufacturer's code was "bes". Kimmel also made the "NF Phasenuhr" (audio frequency phase-indicator, with 360º scale) that was part of the on-board equipment of the 1943 Lorenz VHF rotating-phase navigation system "Erich" (very similar to the VOR system developed in parallel in the USA). Like "Bernhard/Bernhardine", the "Erich" system also used the EBl 3 radio receiver.
The next photo shows the inside (above the chassis) of the HS120. The main components are (left to right): dual Hell printing module, reel for blank paper tape, vertically installed motor, reel for printed paper:
Fig. 26: Top-view of the inside of an HS120 with Werk-Nr. 70346
(original unedited photo: ©2010 L. Hunter, used with permission)
Fig. 27: Top-view diagram of an HS120 Hellschreiber
(source: adapted from Figure 13 in ref. 15)
Fig. 28: The 6-start spindle and sync-magnet of an HS120 printer
(original photo: ©2010 Leonard Hunter, used with permission)
The three electro-magnets are specified as follows (ref. 15, p. 33):
- Printer solenoids ("Leitstrahlmagnet" and "Kennzeichenmagnet"): 4500 turns of 0.1 mm CuL ("Kupferlackdraht" = enameled copper wire, a.k.a. magnet wire), DC-resistance of 480 ohms.
- Synchronization solenoid ("Synchronisiermagnet"): 5500 turns of 0.1 mm CuL, DC-resistance of 510 ohms.
To avoid a paper tape mess in the cockpit, the paper tape is unwound from one spool, and wound onto a second spool (like in a reel-to-reel tape recorder). To minimize paper consumption (and the hassle of having to replace rolls of paper tape in flight), the paper transport motor was only enabled when the strength of the received signals exceeded a certain minimum value. I.e., a "squelch" function. This way, the paper moved during less than 10 sec per minute (3-5 sec per antenna revolution, equivalent to 36-60 deg change in antenna azimuth). After passages of the beacon's beam, the paper tape would stop moving, and the operator could interpret the print-out.
Fig. 29: Rear-view of an HS120 Hellschreiber - Werk-Nr. unknown
(modified for use with two standard-width paper tapes, instead of a single wide tape)
The HS120 is powered by a 24 Volt DC motor, running at 3000 rpm. It was a model SMKO, made by the "Stark-Motor" company of Berlin. Before the war, Stark made electric motors and alternators for the automotive industry. Stark motors were also used in Luftwaffe aircraft, including servo-motors for bombsights.
Fig. 30: Label on the motor - 24VDC, 12 watt, 3000 rpm
(Motor type "SMKO", as specified in ref. 15)
The company was owned by Hans Stark:
Fig. 31A: Listing in the electric motor section of the 1943 Berlin phonebook (Teil II, p. 165)
(with advert for "small rpm-controlled electric machines"
Fig. 31B: Listing in the electric motor section of the 1951 Berlin phonebook
(still at the same address as in 1943)
Fig. 32: Right-hand side of an HS120 Hellschreiber - Werk-Nr. unknown
(two stacked felt ink rollers left of center; note synchronization mechanism for the upper printer channel was removed)
The bottom of the HS 120 shows how the single motor drives the shaft of the printer spindles and the paper tape transport (Figure 33). All capacitors and inductors are also located here (ref. Figure 7). The spool for the printed paper tape is driven via a spring belt that can slip (top right in Figure 33); this tensioning mechanism is needed, as the speed of the spool depends on how much paper tape is wound onto it.
Fig. 33: Bottom of the HS120 Hellschreiber
(original photo: ©2010 Leonard Hunter, used with permission)
Fig. 34: The stacked electromagnets, with their hammer blade against the paper tapes
The following marking is engraved on the back side of the plastic backlighting panel of the HS120: "A. BAJANZ, Berlin -- DRGM;DRP.angem." The Bajanz company manufactured acrylic glass parts (common trade names are plexiglas and perspex), including canopies for military planes (e.g., Heinkel). The abbreviations DRGM, DRP, and angem. respectively stand for "Deutsches Reichsgebrauchsmuster" (model - or patent, in the proper sense of the latter word). This implies "registration without patent protection", "Deutsches Reichspatentamt" (the patent office), and angemeldet: "applied for" ("pending").
Fig. 35: Marking of the manufacturer of the plexiglas front panel
Here is a 25 sec video clip of this printer in action:
An HS120 printer in actionNote: this machine (without Werk-Nr.) was modified to use two standard Hell paper tapes, instead of one wide tape. It also has regular 2-turn spindles, hence, cannot print single-line symbology.
"BERNHARDINE" PRINTER MODEL "Psch 120"
The Psch 120 "Peilschreiber" (bearing printer) was built by Siemens & Halske A.-G in Berlin (p. 188 in ref. 44). They had the military manufacturer code "eas". This code was used for all Siemens plants, such as the Wernerwerk telecom design and manufacturing plant in Berlin-Siemensstadt, were other Hellschreibers were built. Siemens also made the RDFS 120 "Rahmen für Drehfunkschreiber" (the mounting frame for Psch 120), and a "Papierbehalter für Peilschreiber" for storing (used) paper tape of the Psch 120.
There are suggestions in 1945 Allied post-war reports that the development and prototyping labs of C. Lorenz A.G. in Falkenstein/Thuringia (some 100 km southeast of Nürnberg) were involved with this printer (ref. 54). A number of development labs (some 700 employees, no production) were moved there in August of 1943, from Lorenz in Berlin (ref. 55).
Fig. 36: Peilschreiber (bearing printer) "Psch 120" of the FuG 120a - a compact paper tape printer
(source: page 101 in ref. 3)
Fig. 37: Photo of another "Psch120" unit
(source: ref. 7B)
"BERNHARDINE" PRINTER MODEL "Psch 120A"
Peilschreiber 120a (Psch 120a) is the printer of "Berhardine" FuG 120b system. It is a "paperless" printer. The idea was to avoid time-consuming replacement of a full roll of tape during flight, and avoid running out of tape altogether.
The 1939 patent 767513 proposes a bearing printer that uses an endless 3-layer printing tape. This tape is a triple-layer sandwich of wax-covered dark paper, thin silk tape, and thin protective celluloid tape. This technology actually dates back to ca. 1923, when a two-layer version was patented (but not invented) by R.A. Watkins of Illinois/USA (later Watkins-Strathmore Co, until acquired by Western Publishing Co. in 1957). The original implementation consisted of a piece of black waxed cardboard and a translucent grey plastic sheet. One would write or draw on it with a plastic stylus, not unlike today's Personal Digital Assistants (PDAs). This quick-erase slate was called "Magic Slate", and became popular all over the world. In the USA, one can rather easily patent pre-existing devices and methods, so the Bernhardine Wachsschreiber was (re-)patented there in 2003 (US Patent 6,578,615) by the Hewlett-Packard (HP) company.
Fig. 38: A "Magic Slate" note pad or doodle pad
In patent 767513, an endless tape moves around a drum. Spring-loaded rollers are used to maintain tension in the three layers of the tape. The layers are joined just before entering the printer window. Where the printer-spindle applies pressure to the tape, the silk tape sticks to the waxed paper and the pressure points become visible. Erasing is done by separating the silk tape from the waxed paper with a knife blade, after passing the printing window. See Figure 33. This is referred to as a "Wachsschreiber" or "Folienschreiber", i.e., a wax or foil (film) printer. This method was actually implemented during the 1936/37 development by Telefunken of the "Bernhardine 1m mit Wachsschreiber" of the initial UHF Bernhard/Bernhardine system (300 MHz, λ = 1 m). Ref. 2.
Fig. 39: Concept of a "Bernhardine" erasable tape wax-printer
(source: adapted from Figure 3 and 4 in patent 767513)
Whereas patent 767513 proposes an endless tape, the 1940 patent 767536 proposes a triple-layer erasable disk. See Figure 40. Note that the threads on the two printer spindles are oriented the wrong way (turned 90 deg). The latter patent suggests that the drum-shaped wax printer has some serious disadvantages: 1) the tapes wear out and entire spare "drum + tape" modules must carried on the aircraft, and 2) imperfections in the drum surface (bumps, seams, out-of-round tolerances) cause failures.
Fig. 40: Erasable-disk "Bernhardine" wax-printer
(source: Reichspatent Nr. 767536 , see patent table below)
Supposedly the erasable disk concept corrected these shortcomings. This is what was actually implemented in the Psch 120a "Bernhardine" printer. See Figure 41. It has about the same shape and size as the Psch 120 printer. Clearly, replacing an erasable disk would be easier than replacing a drum or installing a new tape, esp. given the tape tensioners. However, even replacing a disk would not have been easy either, given that the layer-separating blade must be inserted between two layers - without damaging the disk. This cannot have been easy, esp. not not with gloves and while maneuvering the aircraft or during a bumpy flight. Indeed, the disk printer proved inadequate in operation: too complicated and unreliable. It was taken out of service, and retrofitted back to the Psch 120a paper tape printer.
Fig. 41: Peilschreiber "Psch 120a" of FuG 120b - an erasable disk printer
(source: page 101 in ref. 3; the large round "Dunkel-Hell" knob is for the ""dim/bright" setting of the "dial" light)
In the photo above, the printed compass rose segments cover about 30 degrees of azimuth. The bearing value "34" ( = 340 deg) is repeated 3-4 times during each pass, which means that the signal was not sent by a real ground station. Also, the station identifier is "D+" or "DT", rather than the standard single letter. These plots were probably created with a test signal generator at the factory. The photo also shows that the disk has room for about 5 passages of the beam of the ground station, before the oldest plot is erased.
Fig. 42: Enlargement of the PSch 120a photo above
THE PRINTER OF "BERNHARDINE" FuG 120k
Towards the end of the war, a much simplified Bernhard/Bernhardine system was under development. Its Bernhardine system was the FuG 120k, where "k" stands for "klein", i.e., "small". FuG 120k did not have the two-channel tone filter unit. Also, the printer-amplifier unit only had one channel and did not have the circuitry for creating the bar-graph of the signal strength. Hence, the actual printer only had a single printer mechanism, printed on narrower paper tape, and had no cam wheel on the spindle shaft. This made the entire system, and the printer, much smaller, lighter, and cheaper. It was intended for installation in single-seat fighter aircraft, where there is little space. Possibly also for the Ju-88 (ref. 8).
Clearly, this Hellschreiber printer can only print the azimuth signal form the "Bernhard" ground station. There no longer is a pointer, previously formed by the V-shaped dip in the signal-strength track. One way to determine the azimuth, is to visually determine the azimuth value in the middle of the azimuth plot. This is not so simple. But what if the azimuth signal is not transmitted via the single-lobe antenna system of the Bernhard beacon, but via the twin-lobe antenna system? Now the signal strength of the azimuth data has a dip when the null of the twin-lobe radiation pattern sweeps by the aircraft! See Figure 37B. As a result, the achievable accuracy was reduced from 0.5º or 1º, to ≈4º (see p. 87 in ref. 2, p. 125 in ref. 21, line item 56 in ref. 8).
Fig. 43A: Separate signal-strength bar graph and azimuth scale - high accuracy
Fig. 43B: Azimuth data transmitted via the twin-lobe antenna system - reduced accuracy
Note that is concept is already mentioned in the original 1936 Lohmann/Telefunken main patent 767354. It also implies a simplification of the Bernhard ground station: only one transmitter is needed, and the single-lobe antenna array is no longer needed.
No photos or diagrams of this printer model are available. It does not appear that this printer, and the associated modified "Bernhard" ground station, ever went into service.
PRINTER AMPLIFIER SV 120 (SCHREIBVERSTÄRKER)
SV 120 ("Schreibverstärker") is the dual-channel printer amplifier unit of the FuG 120. All Hellschreibers require a "tone-detector plus printer-solenoid driver-amplifier" (see Figure 44). It converts received tone-pulses to energization pulses for the printer's electro-magnet. The audio input signal is amplified, band-pass filtered, rectified. A final amplifier acts as a power-switch.
Fig. 44A: Simplified principle diagram of a standard Hellschreiber printer-amplifier channel
However, the SV 120 is much more than just two such channels - see Figure 45. In total, there are 13 tubes (valves): five RV 12 P 2000 pentodes, five LV1 low-noise power pentodes, and three LG6 dual-diodes (full-wave rectifiers).
Fig. 44B: SV120 tubes RV12P2000, LV1, and LG6 (to the same scale)
Fig. 45: Simplified principle diagram of the SV 120 printer amplifier unit
(source: adapted from Appendix-b in ref. 15)
Let's walk through the above block diagram. The first block is the pre-amplifier with one RV 12 P 2000 pentode tube (valve):
- The input is audio from the EBl 3 receiver.
- The volume control potentiometer is located on the HS 120 printer unit.
- The output of the pre-amp goes to a separate dual-channel audio filter unit, the SG 120.
Fig. 46: Pre-amplifier and filter
In the SV 120, these two audio signals are each passed through a separate two-stage amplifier. Each amplifier comprises an RV 12 P 2000 pentode followed by an LV 1 pentode.
The output of the 2-stage amplifier for the bar-graph printer is transformer-coupled to two other stages:
- one for the 1800 Hz constant tone - for the bar-graph printer.
- one for the 2600 Hz Hellschreiber tone pulses - for the azimuth printer.
In the SV 120, the two filtered audio signals are each passed through a separate two-stage amplifier. Each amplifier comprises an RV 12 P 2000 pentode followed by an LV 1 pentode.
The output of the 2-stage amplifier for the bar-graph printer is transformer-coupled to two other stages, see Figure 47:
- An Automatic Gain Control (AGC) stage. Its output goes back to the EBL 3 receiver. Remember that the purpose of this printer channel is to print the strength of the signal from the twin-beam of the Bernhard beacon. This AGC has a short attack time, and a very long decay time. These time constants ensure that the AGC-signal is fairly constant during the entire passage of the beam (3-5 sec), so as not to distort the sharp signal minimum between the two main beam-lobes. It also ensures that side-lobes and rear-lobes of the antenna pattern do not cause the printer motor printer magnets to be enabled. Via the AGC, the side- and rear-lobes actually help prevent the receiver gain from becoming too high. The gain of the AGC-amplifier is high, and a threshold is applied at the input. This AGC makes the performance of "Bernhardine" relatively independent of the distance to the beacon.
- A rectifier/amplifier. Here, the amplitude of the received 1800 Hz tone is first converted to a DC voltage level. Then a sawtooth signal is added, and finally a fixed bias voltage is added. The summed voltages are input to the control grid amplifier tube. This tube acts as a switch, with a small hysteresis. This effectively converts the amplitude of the tone signal to the width ( = duration) of pulses. These pulses are amplified and used to energize the printer-magnet of the bar-graph printer. For a pulse with maximum duration, the printer prints a full-height bar. In absence a pulse (zero width), no bar is printed. The required sawtooth signal is generated by quickly charging a capacitor via a contact that is actuated by a notched wheel on the shaft of the printer-spindle. The capacitor is discharged via a choke coil. The principle schematic of this pulse-width modulator is discussed further below.
Fig. 47: Receiver-AGC and bar-graph printer driver
The output of the 2-stage amplifier for the azimuth printer is transformer-coupled to three other stages, see Figure 48:
- an Automatic Gain Control (AGC) stage. Its output goes to the first tube of this 2-stage amplifier. The AGC keeps the signal level of the received 2600 Hz Hellschreiber tone pulses (azimuth data) constant.
- a rectifier/amplifier. Here, the received 2600 Hz tone pulses are rectified. The rectified pulses turn the driver-amplifier on/off, to energize both the printer-magnet of the azimuth printer, and the synchronization magnet-solenoid.
- a second rectifier/amplifier. This detector is used to start and stop the entire HS 120 printer. Via relay contacts, the motor is turned on, the anode voltage of the two printer-solenoid driver tubes is enabled, and the AGC output to the EBL 3 receiver is enabled. The detector has a hang-time of 1.5 sec, to avoid that the relay de-energizes the system too quickly when the audio signal levels go down. The purpose of this, is to only print (and use paper) when the main beams of the beacon are being received. Once the bar-graph and compass rose segment are printed, the paper does not move until the next beam passage, some 30 seconds later. This makes it easier for the crew to read the print-out.
- Ref. patent 767527 proposes "a simple method" for start-stop control of the printer system, without using complicated things such as AGC. This involves a notched disk that is "somehow" closely synchronized to the rotation of the beacon's antenna system. The width of the notch corresponds to that the azimuth segment of interest. It actuates a switch that enables the printer. The position of the switch is adjustable, so as to be able to pre-select the azimuth segment. This patent has two weak points: 1) undefined synchronization method that is simpler than AGC, and 2) to be able to adjust the switch position, the bearing must already be known - which defeats the purpose of this method.
Fig. 48: AGC and printer-magnet drivers for the azimuth printer
According to patent 767354, the field-strength of the received continuous signal could vary as much as 1:10000 (80 dB amplitude ratio) between maximum and the deep null, necessitating a receiver/filter characteristic with compressing/limiting gain curve. The received signal strength obviously depends on the altitude of the aircraft and its distance (range) from the beacon. Patent 767526 foresees an automatic gain control, using yet a third signal transmitted by the ground-station, via an omni-directional antenna system. However, this was never implemented in the Bernhard/Bernhardine system.
PULSE-WIDTH MODULATOR (PWM) OF THE SV 120
The height of each printed bar must correspond to the signal strength at that moment. In a Hellschreiber printers, the height of a printed line segment is equivalent to the duration of the energization pulse that is applied to the printer's magnet-solenoid. Hence, the pulse duration must be between zero and 100% of the time that the printer-spindle takes to print one complete pixel column. So, to make this work, the amplitude of the received signal must be converted to the width of an energization pulse. This is done in two steps:
- Conversion of the amplitude of the received tone signal to a DC-voltage. The signal amplitude is determined by a conventional tone detector that is found in all standard Hellschreiber printer-amplifiers. It consists of a pre-amplifier, followed by a full-wave diode rectifier and a simple smoothing filter. This converts the momentary amplitude to an equivalent DC voltage level.
- Conversion of this DC-voltage to the width of the energization pulse. Each printed signal-strength bar must start at the bottom of the printed track. This means that the start of the energization pulses must be synchronized to the position of the continuously turning printer-spindle. The synchronized pulse-width conversion is done by the clever circuitry shown in Figure 49.
Fig. 49: Principle circuitry for voltage to pulse-width conversion
(source: adapted from Figure 4 in Rudolf Hell's patent 730625)
The drive-shaft of the printer-spindle (item 11 in the schematic above) has a notch (item 17). It actuates a switch (item 18) once per revolution of the spindle, when the thread of the spindle passes through its start position (bottom of the printed vertical line). Closure of the switch causes a capacitor (item 23) to be step-charged with a fixed supply voltage (item 24). As soon as the switch re-opens, the capacitor begins to discharge across a resistor (21). The value of the capacitor and its bleed resistor are chosen such that the discharge time is equal to (or slightly larger than) the duration of a single spindle revolution. This creates a sawtooth voltage, with a fixed amplitude and period. Clearly, the capacitor voltage is not linear but an exponential curve. The simplified schematic above does not show components that linearize this curve. Note that in the actual SV 120, the capacitor discharges via a choke coil, rather than a resistor.
The DC-amplitude EM of the received constant tone signal is applied across resistor (22). This superimposes EM onto the capacitor voltage. This sum is then offset with a fixed negative grid-bias voltage (20). The latter voltage is chosen such that if the input signal is zero, the anode current of the tube (valve, 19) is too small to energize the printer-solenoid. As soon as an input signal is present, the gain of the tube causes the anode current to exceed the energization level of the printer solenoid, and the spindle begins to print a line across the paper tape (bottom to top). For a small EM, the resulting energization pulse is short, and a short signal-strength bar is printed. For a large EM, a long signal-strength bar is printed. This analog technique is now referred to as "intersective pulse-width modulation", and was re-patented in the USA in the 1960s, with follow-on patents even after the turn of the century!
Fig. 50: Signal-level to pulse-width conversion and printing of the bar-graph
(adapted from Rudolf Hell's patent 730625)
Note that the above circuitry is for a printer spindle that has a single thread that is wrapped once around the hub of the spindle. However, the actual hub of the "Bernhardine" bar-graph has six partial threads (each covering 60° of the hub's circumference). This means that the spindle prints six consecutive columns per revolution of the spindle. To make this work, this printer has six notches on the spindle shaft, instead of just one. The pulse-width conversion circuitry is exactly the same, with the exception of the time-constant for discharging the timing capacitor.
Fig. 51: Plot of the actual pulse-width (h1 - h5) for a linearly increasing input-signal amplitude
(source: adapted from ref. 46)
FILTER UNIT SG 120 (SIEBGERÄT)
The "Bernhard" navigation beacon has two AM transmitters. Their carrier frequencies were spaced 10 kHz. One carrier was modulated with a constant 1800 Hz tone. This creates sidebands at 1800 Hz above and below the carrier frequency. The second carrier was modulated with a 2600 Hz tone. Hence, this carrier also has sidebands: 2600 Hz above and below the carrier frequency. However, the 2600 Hz tone is on-off-keyed with Hellschreiber-pulses. So, each of the 2600 Hz sidebands itself has an infinite Fourier-series of sidebands. As these tone pulses are not a square-wave, the latter sidebands are not individual frequencies (like a comb), but are "smeared" into half sine-wave envelopes. See Figure 52. The tone-pulse transmitter limits the bandwidth of the sidebands to 400 Hz. This is sufficient to pass the 2nd harmonic of the tone pulses (350 Hz), and guarantee proper printing.
Fig. 52: RF spectrum of the "Bernhard" transmitter outputs
(source: frequencies taken from ref. 15)
The FuG120 "Bernhardine" is operated in combination with an EBL3 shortwave AM navigation receiver. The audio output of the EBL3 contains both the constant tone from the "Bernhard" beacon's twin-beam antenna, and the Hellschreiber tone pulses that represent the azimuth symbology. See Figure 53.
Fig. 53: Audio spectrum of the EBl 3 receiver output
The detector-amplifiers of the the two "Bernhardine" Hellschreiber printers respond to all audio signals that have sufficient amplitude - including noise. But the bar-graph printer should only respond to the 1800 Hz tone signal, and the azimuth printer only to the 2600 Hz signal. This means that the two detector-amplifiers must each be preceded by a filter that only passes the tone frequency of interest. The two required bandpass filters are located in the 2-channel SG 120 audio filter unit ("Siebgerät"). See Figure 54. This unit has the Luftwaffe Gerät-Nummer 124-977-A (ref. 15).
Fig. 54: Block-diagram of the SG120 2-channel audio filter unit
Each filter channel comprises a number of series and/or parallel LC-circuits, of which two pairs are stagger-tuned: two parallel-LC circuits in series, or two series-LC circuits in parallel, with slightly different resonance frequencies. The bandpass filter for the Hellschreiber tone pulses has a bandwidth of 400 Hz (ref. 15). Obviously, the center-frequency of the two bandpass filters is the same as the modulation tones of the transmitters: 1800 and 2600 Hz, respectively. Unfortunately, the manual only list the values of all the capacitors, but not of the inductors. So the actual filter characteristics can not be reconstructed (unless an intact SV120 unit is found).
Fig. 55: Audio spectrum of the two SG 120 filter-channel outputs
The outputs of the filter unit are returned to the SV120 printer-amplifier unit.
The SG120 was manufactured by Siemens Luftfahrtgerätewerk (LGW) Hakenfelde GmbH (p. 188 in ref. 44). LGW was located in the borough of Berlin-Spandau, just across the Havel river next to Siemensstadt. LGW was a 1940 spin-off of Siemens Apparate und Maschinen GmbH (SAM). Its military manufacturer code was "hdc"; the code "hnu" was used for international (export) products. LGW made a wide variety of aircraft equipment, such as gyros, temperature gauges, radio altimeters, course indicators, switches, connectors, indicator lights, course guidance equipment, and autopilots.
SWITCHING UNIT UG 120 (UMSCHALTGERÄT)
During approach and landing, the EBl 3 beacon receiver works together with the EBl 2 marker-beacon receiver. In this configuration, the EBl 3 receives an automatic gain control (AGC) signal from the EBl 2, and the EBL2 receives the audio frequency (AF) output of the EBl 3. When the EBl 3 is to work with the "Bernhardine" system, the FuG 120 takes the place of the EBl 2.
This re-configuration is done with the SpKf 1a mode switch. This is just a re-labeled standard SpKf 1 "Sprechknopf" switch. The latter is used to switch a microphone on and off, like a push-to-talk switch (PTT). It has switch positions that are labeled "EIN" (on) and ""AUS" (off). Model 1a has the labels "LFF" ("Landefunkfeuer" = Landing Beacon) and NFF ("Navigationsfunkfeuer" = Navigation Beacon).
Fig. 56: Principle diagram of the UG 120 switching unit
(source: adapted from Figure-7 and Appendix-e in ref. 15)
The mode switch controls the UG 120 switching unit. This is basically a small box with a 4P2T relay (4 sets of changeover contacts). The normal cable that connects the EBl 2 and EBl 3, is replaced with two cables that plug into a splitter/coupler unit: the ZLK VIII S 3 ("Zwischenleitungskupplung"). A third cable connects this coupler to the UG 120 switching unit. In the "LFF" position, the EBl 3 is connected to the EBl 2. In the "NFF" position, the EBl 3 gets its AGC input signal from the FuG 120, and the FuG 120 gets the AF output from the EBl 3.
Fig. 57: Letterhead of Friese & Höpfner
The SpKf 1a mode switch (Ln28986) and ZLKVIII coupler were manufactured by "Frieseke & Höpfner, Spezialwerke für Flugfunktechnik" in Berlin Potsdam-Babelsberg and in Breslau. Their manufacturer code was "gqd" (p. 188 in ref. 51).
POWER SUPPLY U 120 (UMFORMER)
The U 120 power supply unit includes an "Einanker Umformer": a single-rotor motor-generator-alternator (MGA). It generates 300 VDC and 17 VAC. Its 24 VDC motor is powered by the standard 28.5 VDC aircraft electrical system (note: 28.5 VDC is the charging voltage for 24 VDC lead-acid batteries, like 13.8 is for 12 VDC batteries). The MGA, model ZA-FGGW 95b 60, was manufactured by the Ziehl-Abegg company of Berlin-Weißensee. This company also made motors for the electric locomotives of the "Bernhard" ground station. All connections to and from the MGA are passed through line-filters, to suppress commutator noise.
The U120 has five outputs, that all go to the SV 120 amplifier unit.
The 300 VDC generator output is used for three of the five outputs:
- 300 VDC is taken directly from the 300 VDC generator, and is not stabilized. It used as anode voltage for the printer driver tubes (final amps) in the SV 120. Upon power-up, this output is kept disabled ("open") with a time-delay relay, until the rectifier tube for the 280 VDC grid bias voltage (derived from the 17 VAC) has warmed up. This is done to avoid damage to the driver tubes, and to avoid the HS 120 Hellschreiber from starting up inadvertently.
- 280 VDC is obtained by passing the 300 VDC through a choke coil and a filter capacitor. It is used as the anode voltage for all other tubes in the SV 120.
- 140 VDC is the grid-bias voltage for the tubes in the SV 120. It is derived from the 280 VDC with a voltage stabilizer tube Metall Stabilovolt type M STV 140/60 Z. The voltage across this stabilizer is 140 Volt at a nominal current of 35 mA; its max current is 65 mA. This tube is also know as the LK121, where L = "Luftfahrtröhre" (aviation tube) and K stands for "Konstanthalter" = stabilizer, ref. 57.
Fig. 58: Principle diagram of the U 120 power supply of the FuG 120
(source: derived from Appendix-d of ref. 15)
The 17 VAC from the alternator is passed through a transformer. The transformer has four secondaries. Two of the secondaries are up-transformed. Each is full-wave rectified with a LG 6 dual-diode (nominal 400 volt and 100 mA). Here again L = "Luftfahrtröhre", and G stands for "Gleichrichter" = rectifier. This tube was originally developed by Philips. The other two secondaries are down-transformed, to provide the required 12.6 VAC heater voltage to these two rectifiers.
- 280 VDC is obtained by filtering the output of one of the two rectifiers. It is stabilized with two 140 Volt stabilizer tubes in series. This voltage is used as grid bias for the printer driver tubes in the SV 120.
- 140 VDC is obtained by filtering the output of the second rectifier. It is stabilized with a single 140 Volt stabilizer tube. This is used as the bias voltage of the sawtooth signal generator circuit in the SV 120.
Fig. 59: LG6 tube and Metall Stabilovolt M STV 140/60 Z tube (without extraction knob)
AIRCRAFT (INTENDED TO BE) EQUIPPED WITH FuG 120 "BERNHARDINE"
An estimated 2500 Bernhardine units were installed in various aircraft types (ref. 2, primarily night fighter versions), such as the Messerschmitt Me262 (one of my all-time favorite aircraft), but not in the Me262 day-time fighter version (ref. 58A). Installation in the Me 262 "bad-weather" fighter ("Schlechtwetterjäger") was decided in December of 1944; this was configuration "A 1 U 2" of the Me-262 (ref. 59). However, it was cancelled due to lack of availability of the equipment in sufficient numbers (possibly due to Allied bombing of German electronics factories, ref. 60). It was removed from the aircraft equipment list early January of 1945 (see handwritten note in ref. 59). An RAF report on the Me 262 B-2a, also describes the FuG 120a as equipment intended for that type (ref. 63). The Me 262 B-1a/U1 "Rote 8" ("Red 8") of the Luftwaffe's 10./NJG 11 (10. Staffel of Nachtjagdgeschwader 11) is in the collection of the Ditsong National Museum of Military History (formerly known as the South African National Museum of Military History). It was equipped with a FuG 120a system, which was removed by the RAF prior to shipment to South Africa in 1947. Ref. 167.
A drawing exists that suggests installation of the FuG 120a "Peilschreiber" bearing-printer suspended from the canopy between the pilot and radar operator. While purported to be for the Me 262 B-2, this drawing appears to be of the interim night-fighter Me 262 B-1a/U1. Ref. 61, 62. Several captured Me 262 B-1a/U1 showed some equipment. So far, no photos are available to positively identify the equipment. I do not find "suspension from the canopy" credible: the suspended equipment would move upward with the canopy when the canopy is opened, and break all wiring. Also, this would be less table during vibration. Fig. 60 below shows equipment on top of the panel between the pilot and the navigator/radio-operator behind him - not suspended.
Fig. 60: The night-fighter version of the Me-262 - the world's first operational jet-powered fighter
(source: www.footnote.com, no copyright (US Gov't))
Fig. 61: FuG 120 mounting frames on wooden fuselage-mounted panels inside an Me 262 B-1a/U1
(ref. 168; original un-annotated Me 262 photo © EN-Archive, used with permission)
Other types of aircraft equipped with a FuG 120 were Junkers Ju 88G (ref. 58C, 64), Junkers Ju 388 (ref. 58B, 65), Arado Ar234 "Blitz" (ref. 66), and Dornier Do-335 A-6 "Pfeil" (though the latter probably did not enter into active service). It may also have been installed in the Dornier P.254 (Do 435). FuG 120k appears to also have been intended for the brilliantly advanced flying-wing Gotha GO-P60 (Gothaer Waggonfabrik, GWF). Flight tests were also done with a Dornier Do-217 M multi-role bomber (line item 20 in ref. 49).
Fig. 62: Dornier Do-335 "Pfeil" with push-pull propeller arrangement
Fig. 63: Arado Ar-234 "Blitz" - the world's first operational jet-powered bomber
Fig. 64: Junkers Ju-388J night fighter
Fig. 65: Junkers Ju-88
Shown below are excerpts from the two flight log books of Konrad Rösner (ref. 166). For 1944, there are five flights in a Ju-88 (incl. the night fighter variant G1) for which the remarks column mentions flight testing the "Berhardine" system. Rösner was stationed at Twente airbase in The Netherlands, close to the Dutch-German border. The airbase is half way between the "Bernhard" beacons at Schoorl (Bergen) in The Netherlands (ca. 155 km to the northwest) and Buke in Germany (ca. 155 km to the southeast ). It is also ca. 330 km southwest of the "Bernhard" at Bredstedt in Germany (ca. 30 km southwest of Flensburg). Note that in the remarks column, "Flensburg test/guidance" refers to the FuG 227 "Flensburg" radar homing device, and not to a fighter control station at the town with that name (there was no such station there).
Fig. 66: Excerpts from WW2 flight logs of Luftwaffe radio operator Konrad Rösner
(ref. 166; source: courtesy Walter Waiss (archivist of the "Traditionsgemeinschaft Boelcke e.V."), used with permission)
Fig. 67: Translated transcript of Fig. 58
THE FuBl RADIO-NAVIGATION RECEIVER SYSTEM
Standard radio-navigation systems for instrument approaches ("blind landing" = by reference to instruments only) were the "Funk-Blind-Landeanlage" FuBl 1 and the FuBl 2 (initially written with a roman numerals I and II). Ref. 31, 32, 67, 68, 69. The airborne part of the FuBl 1 system is the EB.3, a militarized version of the Lorenz EB.2. This system was patented in the early 1930s by Ernst Kramar (Lorenz Co.) and was successfully commercialized for civil aviation around 1937. The principles of the system are used worldwide to this day (ILS - Instrument Landing System, which even uses the original tone frequencies). The ground station (fixed or mobile) had a 500 W transmitter system, the Ansteuerunsgsender AS 2.
The FuBl 2 was basically an FuBl 1 with an extended frequency range and increased sensitivity, to make it work with the Knickebein, Bernhard, and Hermine systems. The airborne system included both a Lorenz EBl 2 and an EBl 3 receiver.
- The EBl 1 "UKW-Blind-Einflugzeichen-Anlage" is a marker-beacon receiver that covered the 30-31.5 frequency range, plus 33.33 MHz (2 selectable frequencies; range limited to ca. 30 km).
- The EBl 2 "Markierungsfunkfeuerempfänger" is marker-beacon receiver with a fixed frequency of 38 MHz. It indicates passing of fan-marker beacons that are placed at fixed distances from the runway, on the extended runway centerline. The EBl 2 was made by Lorenz, but also manufactured under license by Philips, in its factory in Vienna/Austria (ref. 31).
- The EBl 3 is an AM superhet receiver for VHF landing-guidance beam systems ("UKW-Blindflug-Leitstrahl-Anlage". It provides a lateral guidance signal (left/right deviation) to an AFN-2A indicator (Anzeigegerät für Funk-Navigation") and to a lateral-axis auto-pilot. This receiver was developed by Lorenz AG out of the FuG 16 (ref. 29, 70). It was a replacement for the EBl 1. In combination with navigation beacons such as the Knickebein system, the EBl 1 had insufficient sensitivity for long range navigation (i.e., to targets in England). The EBl 3 was produced by several manufacturers, including AEG Sachsenwerk in Dresden-Niedersedlitz. It comprised seven tubes of type RV12P2000 (schematic: ref. 71), and had an IF of 6 MHz. This receiver has an unusually large bandwidth: ca. 15 kHz. Note that these days, long-, medium- and short-wave AM radio stations only have 5, 9, or 10 kHz channel spacing, and a baseband bandwidth half that size! Initially, the unit had a light-metal ("Elektron") die-cast construction, built by Mahle. Towards the end of the war, the chassis housing and front face were made of simple sheet metal.
There are several EBl 3 models (ref. 72):
- EBL 3H, where "H" stands for "Handbedienung" = manual tuning (hand-crank). It covered 30.0 - 33.1 MHz with 32 channels (100 kHz channel spacing). These were allocated to the "Bernhard/Bernhardine" system. Channel-33 and channel-34 were set to 33.02 and 33.33 MHz respectively. The latter two channels were for "blind landing" purposes (ref. 77). Model 3H1 had a manual tuning module that could be replaced with a remote-controlled tuning unit.
- EBL 3F, where "F" stands for "Fernbedienung" = remote-control tuning. It had no Channel-34, and Channel-33 was set to 33.33 MHz.
- EBL 3G is basically an EBL 3F with +/-15 kHz fine-tuning.
These receivers where normally used in conjunction with landing guidance systems (instrument landing system for "blind" flying). Other than during approach and landing, these receivers could be used or other purposes. The two tone signals transmitted by the "Bernhard" beacon stations were close enough in frequency that they could be received by a single wideband receiver. The two tones were separated by the SG 120 ("Siebgerät") audio filter unit of the "Bernhardine" system, and amplified and rectified in the SV 120 ("Schreibverstärker") unit before being passed to the printer unit.
Fig. 68: Receiver model "EBl 1"
Fig. 69: Receiver model "EBl 2"
The only aircraft actually equipped with the EBl 3 were (ref. 74, p. 106 in ref. 2: the bomber version of the Ar-234, the nigh-fighter version of the Ju-88 and Do-335 (appendix II in ref. 8), Do-217 (ref. 75, 76), and the bad-weather fighter ("Schlechtwetterjäger") version of the Me-109, the Me-262 (ref. 25a, appendix II in ref. 8), Ju-388 (ref. 58B), FW-190, and Ta-152, and the reconnaissance version of the Me-109, Me-262, Ar-234 (planned only, per ref. 74), and Ta-152. The latter is an early 1945 high-altitude interceptor-fighter derivative of the ubiquitous Focke-Wulf FW-190. The designator "Ta" refers to the renowned FW chief-designer, Kurt Tank.
Fig. 70: Receiver model "EBl 3H1"
Fig. 71A: Receiver model "EBl 3H"
(courtesy Erich Werner, used with permission)
Fig. 71B: Receiver model "EBl 3H"
(source: Figure 5.2 in ref. 78)
Fig. 72: "Landeempfänger" EBl 3 (lower equipment row, right of center) in a "Bordfunkanlage" FuG 10 P
(source: Figure 4.4 in ref. 78)
After the war, the small company Curt Höhne Radiomechanik (radio sales & repairs) of Dresden-Radebeul, somehow "acquired" the EBl 3 inventory of the Sachsenwerk factory from the Russian authorities, and converted parts of them to car radios (ref. 79), such as the AS503-OS. Conversions were also published for the 2m (145 MHz) amateur radio band (e.g., ref. 80 from 1952).
Fig. 73: Receiver model "AS503-OS"
"BERNHARDINE" FOR FUG 139 "BARBAROSSA" AND FUG 126 "BALDUR/BORD"
FuG 138 "Barbara" was a small "Kommandoübertragungszusatz" command-uplink attachment to the FuG 25A "Erstling" Identification Friend or Foe (IFF) transponder in bomber and fighter aircraft. This transponder was used in combination with Freya and Würzburg radar systems starting in 1941. The radar system included a transponder interrogation transmitter "Kuh" (125 ±8 MHz), and a "Gemse" receiver (156 MHz) to interpret the 10-bit reply codes of the transponders. Later in the war, the Luftwaffe developed the fighter control system "EGON": "Erstling Gemse Offensiv Navigation". "Barbara" could filter out Morse command messages that were superimposed onto the "Kuh" uplink transmissions. Major disadvantages of this system are that the enemy could also read the command messages, and that it required pilots to pay attention to the Morse signals (distraction) and know how to "read" Morse code (not part of pilot training). See §109-115 in ref. 8.
Late 1944, the FuG 139 "Barbarossa" was developed to "to improve the interference immunity of the "Bernhard" system, as well as simplify and further develop it" (ref. 81), thereby also overcoming the weaknesses of "Barbara". Development started mid-1944 at an institute of the Reichsstelle für Hochfrequenzforschung e.V. (RHF) at Bad Aibling near Munich.
"Barbarossa" was intended to work with the FuG 25A transponder and its successor, the Lorenz FuG 226 "Neuling", which was still in the prototype phase early 1945. Messages were uplinked to the transponder via Pulse-Position Modulation (PPM, a.k.a. Pulse-Phase Modulation), probably developed at Lorenz in Berlin or Falkenstein. This PPM used 30 μsec groups of three pulses. The position of the center pulse was varied in discrete steps, to encode information. PPM provides higher noise-immunity than Pulse-Duration and Pulse-Amplitude Modulation. Up to seven message uplink channels could be active on a single transponder interrogation frequency (ref. 82). The "Barbarossa" system included a filter/decoder unit and a Hellschreiber printer. The printer was developed from that of the FuG 120 "Bernhardine". The filter/decoder unit comprised a tapped delay-line ("Koinzidenzsieb") and converted the PPM signals to Hellschreiber pulse sequences. The first production batch of 200 units (out of an order of 1700 units) was supposed to enter into service in April of 1945 (ref. 83).
FuG 25 and FuG 226 were transponder systems that allowed the ground-station to determine the distance between aircraft and that ground-station (i.e., range). Only a small number of aircraft could be handled simultaneously by the system (and by the ground-controller). Clearly, this is incompatible with independent navigation by aircraft. Allowing the aircraft to interrogate the ground-station, rather than the other way around, solves this. The post-war implementation of this is the civil Distance Measuring Equipment (DME) system and the equivalent military TACAN system, both widely used to this day.
The first (and only) Luftwaffe transponder system that worked like this, was the Baldur system. See §83 in ref. 8. It was developed during 1944 (ref.26A). The system comprised the FuSAn 729 "Baldur" ground-based transponder transceiver, and the FuG 126 "Baldur/Bord" transponder-interrogator transceiver onboard the aircraft. A further development of this was "Baldur K". The onboard FuG 126K system included a Bernhardine-type Hellschreiber printer.
UNKNOWN / UNCONFIRMED / UNCLEAR ASPECTS
The following aspects of the FUG 120 "Bernhardine" system are still unknown, unconfirmed, and/or unclear (to me):
- Inclusion of "degree tick-marks" for in the running commentary command, for printer synchronization
- The manufacturer of the Psch120a printer ("Wachsschreiber")
- The printer Psch120"x" of the FuG120k, and its manufacturer
- Involvement in the development of the Psch120/FuG120a by the Lorenz company in Falkenstein/Thuringia
- Hellschreiber of the FuG 139 "Barbarossa" and of the FuG126k "Baldur K / Bord"
- Hellschreiber of the Lorenz "Sägezahn" command upload system
- The color of HB50 printer ink
If you have any additional information, please contact me!
Below is a listing of patents related to Bernhard/Bernhardine.
|Patent number||Patent office||Year||Inventor(s)||Patent owner(s)||Title (original)||Title (translated)|
|767354||RP||1936||-||Telefunken G. für drahtlose Telegraphie m.b.H.||Verfahren zur Richtungsbestimmung||Method for direction-finding [this is the primary "Bernhard" patent]|
|737102||RP||1937||R. Hell||Dr.-Ing. Rudolf Hell||Verfahren zur Registrierung des Verlaufes veränderlicher Stromkurven||Method for printing the trace of varying signals [Hell printer for signal-level track of Bernhardine]|
|767513||RP||1939||A. Lohmann||Telefunken GmbH||Empfangsseitige Schreibvorrichtung zur Durchführung eines Verfahrens zur Richtungsbestimmung [Wachsschreiber]||Receiver-side printer for the implementation of a method for direction-finding [wax printer, infinite loop, erasable tape]|
|767526||RP||1938||A. Lohmann||Telefunken GmbH||Verfahren zur Richtungsbestimmung||Method for direction finding|
|767527||RP||1938||A. Lohmann||Telefunken GmbH||Einrichtung zur periodischen Ein- bzw. Ausschaltung einer Registriervorrichtung||Device for switching on and off of a printer|
|767536||RP||1940||A. Lohmann||Telefunken GmbH||Empfangsseitige Schreibvorrichtung zur Durchführung eines Verfahrens zur Richtungsbestimmung||Receiver-side printer for the implementation of a method for direction-finding|
|767919||RP||1940||H. Muth||Telefunken GmbH||Verfahren zur Richtungsbestimmung unter Verwendung eines rotierenden Funkfeuers||Method for direction-finding with a rotating beacon [using only twin-lobe beam]|
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 coursepointer, or compass rose info via Nipkow-video]|
|620828||RP||1933||-||C. Lorenz AG||Funkpeilverfahren||Method for direction finding [transmission of compass rose info via Nipkow-video]|
Patent office abbreviation: RP = Reichspatentamt (Patent Office of the Reich), DP = deutsches Patentamt (German Patent Office)
Patent source: DEPATISnet
- Ref. 2: pp. 76-110, 224 in "Die deutschen Funkführungsverfahren bis 1945", Fritz Trenkle, Alfred Hüthig Verlag, 1987, ISBN 3778516477, 215 pp.
- Ref. 3: pp. 94-102 in "Die deutschen Funk-Navigation und Funk-Führungsverfahren bis 1945", Fritz Trenkle, Motorbuch Verlag, 1995, 208 pp., ISBN-10: 3879436150.
- Ref. 4: p. 260 in "A survey of continuous-wave short-distance navigation and landing aids for aircraft", C. Williams, Journal of the Institution of Electrical Engineers - Part IIIA: Radiocommunication, Volume 94, Issue 11, March-April 1947, pp. 255 - 266.
- Ref. 5: pp. 236-237 in "Instruments of Darkness: The History of Electronic Warfare, 1939-1945", new ed., Alfred Price, Greenhill Books, 2005, 272 pp., ISBN-10: 1853676160.
- Ref. 6: "G.A.F. Night Fighters - Recent Developments in German Night Fighting" [transcript], Air Ministry, Air Ministry, Assistant Director of Intelligence - Prisoner Interrogation, Wing Cmdr. S.D. Felkin, A.D.I. (K) Report No. 125/1945, January 1945, 18 pp.
- Ref. 7: "Beiträge der Firma Siemens zur Flugsicherungstechnik und Luftfahrt-Elektronik in den Jahren 1930 bis 1945 (Teil 1 & 2); H.J. Zetzmann, in "Frequenz - Zeitschrift für Schwingungs- und Schwachstromtechnik"
- Ref. 7A: Part 1: Vol. 9, Nr. 10, 1955, pp. 351-360.
- Ref. 7B: Part 2 (pp. 387, 388, 392): Vol. 9, Nr. 11, 1955, pp. 386-395.
- Ref. 8: "Radio and Radar Equipment in the Luftwaffe - II, Navigational Aids" [transcript], Air Ministry, Assistant Director of Intelligence - Prisoner Interrogation, Wing Cmdr. S.D. Felkin, A.D.I. (K) Report No. 357/1945, 1945, 18 pp. Source: www.cdvandt.org
- Ref. 15: "Beschreibung und Betriebsvorschrift für Funk-Navigationsanlage FuG 120" [Description and Operating Manual for Radio-Navigation System FuG 120], Telefunken G.m.b.H., document FN-T-GB Nr. 1932, December 1944, 43 pp. [30 MB]
- Ref. 21: Drehfunkverfahren", pp. 119-130 in “Bordfunkgeräte - vom Funkensender zum Bordradar“, Fritz Trenkle, Bernard und Graefe Verlag, 1986, 283 pp., ISBN 3-7637-5289-7
- Ref. 26: "Bordfunkgeräte - vom Funkensender zum Bordradar", Fritz Trenkle, Bernard und Graefe Verlag, 1986, 283 pp., ISBN 3-7637-5289-7.
- Ref. 26A: pp. 61-63, "Kommandoübertragungszusätze".
- Ref. 26B: pp. 97-103, "Leitstrahl-Verfahren" (beam methods).
- Ref. 29: "A new field application for ultra-short waves", Ernst Kramar, Proc. of the IRE, Vol.21, Nr. 11, November 1933, pp. 1591-1531.
- Ref. 31: "Das Funk-Blindlandegerät" [Fu Bl I, EBl 1, EBl 2, Fu Bl 2, Werner Thote, pp. 20-25 in "Radiobote" - Heft 9, May-June 2007 (Jg. 2) [pdf]
- Ref. 32: "Beschreibung und Betriebsvorschrift für Funklande-Empfangsanlage Fu Bl 1 Ex", DTA 140, C. Lorenz AG, 1940, 59 pp. Source: www.cockpitinstrumente.de
- Ref. 42: pp. 195-197 in "Confound and destroy: 100 Group and the bomber support campaign", Martin Streetly, 2nd ed., Jane's Publishing Co., 1985, 279 pp.
- Ref. 43: AVIA 6/9218 "Amplifier and filter units for FUG 120", 1945, Royal Aircraft Factory / Royal Aircraft Establishment, Examination of Enemy Aircraft.
- Ref. 44: pp. 28, 29, 188 in "Luftwaffe Flugzeug-Ausrüstungsgeräte, Band FA/01", Peter Aichner (author & publ.), 1997, 670 pp.
- Ref. 45: "Luftwaffe Prüfvorschrift FuG 120 ToG 120 PV 120 PV 62" ("Bernhardine")
- Ref. 46: Bild 17 in "Deutsche Funkmeßtechnik 1944: ein Vortrag von Leo Brandt, gehalten am 8. Februar 1944, zur Einführung der Zentimeter-Technik für das Funkmeßgebiet", Leo Brandt, Vol. 7 of Bücherei der Funkortung, Sonderheft, Verkehrs- und Wirtschafts-Verlag, 1956, 29 pp.
- Ref. 47: "Die Entwicklung des Hell-Schreibers" by the inventor himself: Rudolf Hell; pp. 2-11 in "Gerätentwicklungen aus den Jahren 1929-1939", Hell - Technische Mitteilungen der Firma Dr.-Ing. Rudolf Hell, Nr. 1, Mai 1940 [in German]
- Ref. 48: "Fehlerbestimmung und Störbeseitigung bei der Anlage FuG120 an Hand des Schriftbildes" [troubleshooting and problem fixing of the FuG120 based on print-outs], Telefunken document FN/Lit. 1920.
- Ref. 49: §19-23 in "Some further notes on G.A.F. Pathfinder procedure", A.D.I.(K) Report No. 187/1944, Air Ministry, Assistant Director of Intelligence - Prisoner Interrogation, Wing Cmdr. S.D. Felkin, 25 April 1944, 5 pp. Source: www.cdvandt.org.
- Ref. 50: Cover sheet + pp. 2, 3, 196 of "Gerätliste Druckvorschrift D 97/1", Oberkommando des Heeres, Heereswaffenamt, Berlin, 1 July 1943
- Ref. 51: "Bauaufsichts-Leitung des RLM (BAL) in Rüstungsfirmen. Monatsmeldungen 1941-1942", Bundesarchiv-Militärarchiv, Bestand RL 3, Generalluftzeugmeister, Archivalienverzeichnis, Signatur 4376-2427.
- Ref. 52: "Gruppenübersicht der Flugzeug-Ausrüstungsgeräte und Anforderzeichen", Reichsluftfahrtministerium (RLM).
- Ref. 53: "Dienstanweisung für die Bauaufsichten (BAL) des Reichsluftfahrtministeriums", Teil 1, "Aufgabengebiet", 1 August 1940 (supersedes issue of 1 April 1937), Luftwaffen Dienstvorschrift 61/1 (L. Dv. 61/1), 33 pp.; source: www.cdvandt.org.
- Ref. 54: Sheet 7 in Section 0.1 of A.L. No. 35 of Sub Committee for the Investigation of German Electronic and Scientific Organisation (SIGESO), 9/11/1945, Report Vol. 1, Part I. Source: www.cdvandt.org.
- Ref. 55: "Verlagerungsbetrieb C. Lorenz AG Zweigwerk 14 in Falkenstein/Vogtland, 1943 bis 1946", Werner Thote, Arbeitsgruppe Betriebsgeschichte ROBOTRON Radeberg, November 2012, 12 pp.
- Ref. 57: "Luftfahrtöhre LK1221, Metallstabilisator (M STV 140/60 Z)" [datasheet], RLM Luftfahrtsröhren Ringbuch, April 1943, 2 pp.
- Ref. 58: "The Warplanes of the Third Reich" [by far the most complete reference work on German WWII aircraft], William Green, Gallahad Books, 1970, 672 pp., ISBN: 88365-666-3.
- Ref. 58A: pp. 631-632.
- Ref. 58B: p. 517.
- Ref. 58C: p. 470.
- Ref. 59: Protokoll 8 - 262 Nr. 55, geh.Kdos.ES/V/5506, 7 December 1944, Messerschmitt AG, Augsburg (courtesy R.T. Eger stormbirds.com, used with permission)
- Ref. 60: ca. p. 537 in "Wilde Sau": eine textbegleitende Bildchronik", Vol. 2 of "Jagdgeschwader 300 ", W. Berthke, F. Henning, Struve Druck, 2001, 568 pp.
- Ref. 61: Nachtjäger 8-262 B 2, Zeichnung Nr. S8-0084, DLH, 7.2.45, NA(PRO) MR 1-820 (1).
- Ref. 62: "Pioniere des Jet-Zeitalters - die historisch-technische Geschichte der ersten Strahlflugzeuge", Heinz. J. Nowarra, Der Landser Grossband, Band 362, Pabel Rastatt Verlag, 1964, 74 pp.
- Ref. 63: A.I.2.(g) Report No. 2370, dated 23rd August, 1945.
- Ref. 64: p. 15 in "The Junkers Ju 88 Night Fighters - Profile Number 148", Alfred Price, Profile Publications Ltd., 1967, 15 pp.
- Ref. 65: p. 79 in "Ju 188 Ju 388 cz. 2", Monografie Lotnicze Nr. 34, Robert Michulec, AJ-Press, 1997, 82 pp.; the full document (in Polish) is here [49 MB] See note 1
- Ref. 66: pp. 13, 18 in "Blitz!: Germany's Arado Ar 234 Jet Bomber", J.R. Smith, E.J. Creek, Merriam Press, 1997.
- Ref. 67: "He 111 H-6, Flugzeug-Handbuch (Stand August 1942), Teil 9D, Bordfunkanlage mit: FuG X, PeilG V, FuBl I bzw. FuBl 2 und FuG 25", D.(Luft) T.2111 H-6 Teil 9D, Ausgabe September 1942, 65 pp.
- Ref. 68: pp. 97-103 of "Leitstrahl-Verfahren", in “Bordfunkgeräte - vom Funkensender zum Bordradar“, Fritz Trenkle, Bernard und Graefe Publ., 1986, 283 pp., ISBN 3-7637-5289-7.
- Ref. 69: "Übersicht über die Funkgeräte der Luftwaffe", Fub-2, Heft 2 of "Arbeitsunterlagen für den nachrichtentechnischen Unterricht", 1. Auflage, Luftnachrichtenschule, Gr. NTU, Halle (Saale), November 1942, 6 pp. [Übersichtstafel Bordfunk- und Bord-Peilgeräte, Bodenpeilanlagen, Bodensender, Bodenempfänger; Overview tables of airborne radios and direction-finders, ground-based direct-finders, transmitters, receivers]
- Ref. 70: "Die Bordfunkgeräte FuG 16 und FuG 17", pp. 28-49 in "Berühmte Bordfunkgeräte - ein Beitrag zur Geschichte der Elektrotechnik" [FuG 10, FuG 16, FuG 17, FuG 25a, FuG 101a, ...], H. Sarkowski, Expert Verlag, 1983, 80 pp.
- Ref. 71: E Bl 3-H schematic, courtesy Erich Werner, used with permission.
- Ref. 72: "Funk-Landegerät Fu Bl 2 Geräte-handbuch" [EBL 2, EBl 3], D.(Luft)T.4058, February 1943, 120 pp.. Source: www.cdvandt.org.
- Ref. 73: para.11 and 14 in "G.A.F. night fighters. Recent developments in German night fighting", A. D. I. (K) Report No. 125/45, Air Ministry, Assistant Director of Intelligence - Prisoner Interrogation, Wing Cmdr. S.D. Felkin, 27th January 1945. Source: www.cdvandt.org.
- Ref. 74: "Blind landing and airborne communications equipment. Radio and Radar Equipment in the Luftwaffe - II", S.D. Felkin, Air Ministry Directorate of Intelligence, London/UK, A.D.I. (K) report no. 343/1945, July 1945, 6 pp.
- Ref. 75: Werkschrift "Do 217 N-1, N-2 Fleugzeughandbuch, Teil 9D, Bordfunkanlage (stand Oktober 1943)", Ausgabe Dezember 1943, Dornier-Werke G.m.b.H., 94 pp.
- Ref. 76: page in "Do217-317-417 An Operational Record", Manfred Griehl, Smithsonian, 1992, 237 pp.
- Ref. 77: pp. 291 and 350 in "Geschichte der deutschen Nachtjagd: 1917-1945", Gebhard Aders, 1977, 391 pp., Motorbuch Verlag, ISBN-10: 387943509X. Also appeared as translation with revisions: "History of the German night fighter force, 1917-1945", Jane's Information Group, 1979, ISBN 0867205814, 360 pp.
- Ref. 78: "Die Funklandeanlagen", pp. 45-49 in "Die deutschen Funk-Navigation und Funk-Führungsverfahren bis 1945", Fritz Trenkle, Motorbuch Verlag, 1995, 208 pp., ISBN-10: 3879436150.
- Ref. 79: "Blindlandeempf. EBl 3H", courtesy Erich Werner, used with permission.
- Ref. 80: "Der EBl 3 im UKW-Empfänger" [amateur radio conversion to 2 m band], C. Möller, pp. 556-558 in "Funk-Technik - Fachzeitschr. für Kommunikationselektroniker und Radio- u. Fernsehtechniker; offizielles Mitteilungsblatt. der Bundesfachgruppe Radio- und Fernsehtechnik", Vol. 7, Nr. 20, October 1952
- Ref. 81: RL 39 "Forschungsinstitute der Luftwaffe", test report nr. 275,12-Feb-1945, p. 320-323 in "Das Bundesarchiv und seine Bestände", Boldt, 1977, 940 pp.
- Ref. 82: p. 10 in "Evaluation report, Issues 2-112", Combined Intelligence Objectives Sub-Committee (CIOS)
- Ref. 83: "Kriegstagebuch (KTB) - Chef der Technischen Luftrüstung (TLR), Berichtraum 8.1. - 14.1 1945" [war diary]. Source: www.cdvandt.org.
- Ref. 84: "Funk-Landegerät Fu Bl 2 Geräte-Handbuch", Druckschrift D. (Luft) T. 4058, February 1943,120 pp; source: www.cdvandt.org.
- Ref. 85: Files available in the company archive of the Deutsches Technikmuseum, Berlin/Germany:
- Ref. 85B: "Beschreibung des Drehfunkverfahrens - System Telefunken - Teil 1, Verfahrensbeschreibung EC-1-4262 - für die Navigation von Flugzeugen (Exemplar nr. 29 - Handexemplar Leyn) [Description of the Telefunken rotary beacon system, Part 1, for aircraft navigation, copy nr. 29]; Archive file I.2.060C (Fa. AEG-Telefunken), I. Num. 06172, 1943
- Ref. 85C: "Materialsammlung zur Geschichte der Ortung, insbesondere Leitstrahl und Drehfunkfeuer "Bernhard" und "Bernhardine" (FuG 120)" [Material regarding the history of navigation, in particular beams, rotary beacon "Bernhard", and "Bernhardine" (FuG 120); technical description of beam-systems "Wotan I", "Wotan II" (X-System), "Knickebein" (Y-System); correspondence & documents about beam-systems and "Bernhard"/"Bernhardine", drawings of the "Bernhard" installation at Trebbin/Glau, technical description of the Telefunken rotary beacon (part 1) and system description ED1-4262 by A. Lohmann]; Archive file I.2.060C (Fa. AEG-Telefunken), I-Num. 07823, 1942-1967
- Ref. 85D: "Beschreibung des Drehfunkfeuer-Verfahrens "Bernhard" und "Bernhardine" (Geheimmanuskript des "FuG 120"", acquisition by US Air Documents Division T-2, (Technical intelligence arm of the Air Materiel Command, AMC), Wright Field, Dayton/OH; Archive file I.2.060C (Fa. AEG-Telefunken), I-Num. 07756
- Ref. 166: pp. 21, 22, 23, 25 in "Flight logbooks of Konrad Rösner, Part 1 (29-Oktober-1940 - 3-May-1944) and Part 2 (3-May-1944 - 9-April-1945)", courtesy Walter Waiss (archivist of the Traditionsgemeinschaft Boelcke e.V.), used with permission.
- Ref. 167: personal correspondence with the Ditsong National Museum of Military History, February 2011. [pdf]
- Ref. 168: p. 484 in "Me 262", Vol. 3, J. Richard Smith, Eddie J. Creek, Classic Publication, 2007, 224 pp.
- Ref. 169: photo of item in collection of the UK Imperial War Museums with Crown Copyright, used in accordance with the Open Government License [pdf]
- Ref. 170: connector specification sheet "Fl 32 113-6 - Elektrische Geräte 20-pol. Steckverbindung Gerades Anbeugehäuse für 20-pol. Kontakteinsätze", RLM, update of Sept. 1944, 1 p.
- Ref. 171: pp. 50-53 in "Vom hydraulischen Regler zum Prozessleitsystem: Die Erfolgsgeschichte der Askania-Werke Berlin und der Geräte- und Reglerwerke Teltow. 140 Jahre Industriegeschichte, Tradition und Zukunft", Lothar Starke, BWV Berliner Wissenschafts-Verlag, 2010, 272 pp.
- Ref. 173: copy of items in file AIR 14/3577 "Signals investigation on 27 to 35 Mc/s "Windjammer" (1943/1944)". Items are in the collection of The National Archives; material with UK Crown Copyright, used in accordance with the Open Government License [pdf].
- Summary of the contents of ref. 173A-173E.
- Ref. 173A: "'Windjammer" observation", by R.A. Fareday (Noise Investigation Bureau [Electronic Intelligence], N.I.B., London), dated 20th June 1944, 1 page.
- Ref. 173B: ""Possible "Windjammer" transmissions", report by Flight Lieutenant Douglas of 192 Sq., dated 16th December 1943, 1 page.
- Ref. 173C: "192 Squadron Flight report No. 215/43" by F/Lt Robinson to Squadron Leader Burtler, dated 15th November 1943 (actual report by P/O G.F. Evans of 13th November 1943), 6 pages.
- Ref. 173D: "Windjammer – Arcachon", letter from Air Ministry A.I.4. [intelligence branch section supervising RAF Y Service] to Commanding Officer of 192 Squadron, dated 16th July 1943, 1 page + 1 aerial photo.
- Ref. 173E: "The windjammer and Dreh-Elektra", by 192 Squadron Leader J. Whitehead, dated 18th June 1943, 1 page.
- Ref. 175: pp. 512-516, 524 in "Activities at Knockholt", J.A. Reeds, Appendix B in "Breaking Teleprinter Ciphers at Bletchley Park - General Report on Tunny with Emphasis on Statistical Methods (1945)", 1st ed., I.J. Good, D. Michie, G. Timms (J.A. Reeds, W. Diffie, J.V. Fields, eds.), John Wiley & Sons, IEEE Press, 2015, 735 pp.
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