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OVERVIEW

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 other beacon systems during "blind" approach and landing, and in combination with beam systems for guiding bombers and fighter aircraft to their target. The printer system provided 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.

Bernhard Bernhardine system diagram

Fig. 1: "Bernhardine" airborne Hellschreiber printer of the "Bernhard/Bernhardine" radio-navigation system

(click here for a full size image)

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).

HS120 Psch120 mfr

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.

FuBl test rack

Fig. 2: Test rack with FuBl 2 navigation receiver system (left) and rack with FuG 120 "Bernhardine"

(source: Fig. 39 in ref. 181, Fig. 6 in ref. 183, p. 99 in ref. 3)

Of course, the aircraft installation included a number of mounting frames 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, Peilschreibmgerät, 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.

Bernhard beam concept Rotating beacon cartoon

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° and 228.0° 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 1800 Hz tone of the twin-lobe beam), and once the 1800 Hz tone plus the constant stream of 2600 Hz Hellschreiber tone-pulses. The simulated beam-passage duration is about 3½ seconds (≈40°).

Bernhard sound

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



EVOLUTION OF THE "BERNHARDINE" PRINTER

Traditionally, signals from radio-navigation beam beacons were presented on needle-instrument indicators in the cockpit or at the navigator's station in the aircraft. Examples of this are the Anzeigegerät für Funk-Navigation AFN 1 and AFN 2:

needle instrument indicators

Fig. 4: AFN1 and AFN2, with needles for indicating left/right course deviation and signal strength


I have captured the development time-line of the "Bernhardine" printer in tabular form in ref. 204R, based on ref. 204A - 204Q. It all started early 1935, well before WW2: Herbert Muth of the Telefunken company came up with the idea to print the signals of rotating beacons, instead of using a needle-instrument. He also proposed to use the Hellschreiber printer system to do so (ref. 204E/R). The time-line from idea to series production spans well over six years: from early 1935 to at least the fall of 1941. In parallel with the development activities, Telefunken (Adalbert Lohmann, Herbert Muth) and Rudolf Hell patented several fundamental innovations, as illustrated in the time-line diagram of Fig. 5 below. Note that a number of the patents have a post-war patent award date. However, they were actually awarded as "secret patents" before the end of the war, due to their military strategic importance.


Bernhardine time-line patents

Fig. 5: Time-line of the patents related to the "Bernhardine" printers

(see patents section; dates are patent filing dates)

During the spring of 1935, the Telefunken company decided to develop the "Telefunken-Drehfunkfeuerverfahren", a new Telefunken rotating radio-navigation beacon system (ref. 181, 183). Construction of a UHF test/evaluation beacon started in August of 1935. The beacon used a single transmitter, and the sweeping antenna radiation pattern had two strong front lobes with a sharp null between them. This makes it easy to very accurately detect beam passage. The printing concept was demonstrated with a 1-channel ink strip-chart recorder. Experiments and tests were conducted during December of 1935.

These evaluation tests exposed a major problem: exactly when the bearing information (azimuth; direction of the receiver with respect to the beacon, relative to North at the beacon) was most needed, the antenna radiation pattern had a deep null. I.e., impossible to transmit bearing information via this beam! The solution is covered by the March 1936 Telefunken/Lohmann patent 767354. It expands the original single-transmitter/twin-lobe rotating beam beacon with a second transmitter and single-lobe beam pattern that points exactly in the null direction of the twin-lobe beam. It was used to transmit the momentary pointing direction of the single-beam/null as a sequence of Morse-like dashes and dots ("Kennzeichen"). The RLM (Reichsluftfahrtministerium, the German Aviation Ministry) ordered three test stations early 1936. The printers were 2-channel wax paper strip-chart recorders, custom made by the Siemens Messgerätewerk (Wernerwerk M, M-Werk), see Fig. 6. These are thermal recorders: the strip of paper is waxed (or treated with paraffin) so that it turns black when heated. The printing stylus is small loop of heated resistance wire. Strip chart recorders have a long strip of paper that is ejected out of the recorder. Roll chart recorders are similar to strip chart recorders, except that the recorded data is wound onto roll (like a "reel to reel" audio or video tape recorder), and the unit is usually fully enclosed.

Validation testing (including flight tests) of the beacon + printing system was completed about a year later (i.e., spring 1937). The RLM decided to relax its very challenging 0.1° system accuracy requirement, but now required a print-out that was easy to read and interpret (which was not at all the case with the evaluated test systems). Telefunken/Lohmann then took up the 1935 idea of Telefunken/Muth, and proposed to transmit the momentary compass pointing direction of the single-lobe beam in Hellschreiber format, i.e., as bitmap symbology that is transmitted as a stream of binary pixels. However, a method for using a Hellschreiber printer to print the signal strength curve of the twin-lobe "pointer" beam ("Leitstrahl") remained to be found... Telefunken discussed the problem with Rudolf Hell, who then invented the Pulse Width Modulator (PWM), synchronized to the printer spindle of the Hellschreiber printer, to convert signal amplitude into the length of a vertically printed line segment. I.e., a Hellschreiber bar graph representation. Hell patented this in October of 1937 (patent 730625). During the summer and fall of 1937, Rudolf Hell Co. designed and built a PWM printer amplifier. They also modified the printer spindle of a standard Hell Morse practice recorder to interface with the PWM and print six bars per spindle revolution. The first flight test demonstration (to the RLM) with a Hellschreiber beacon-printer took place on November 11th, 1937 (ref. 204E/F/N). Unfortunately, no photo is available of the Hellschreiber printer that was used.

During the fall of 1937, Telefunken/Lohmann conceived and promoted the idea of not using plain paper tape in the Hellschreiber beacon printer, but "Printator" tape. This is 3-layer tape that is erasable by separating the layers. He obtained strips of such tape from the Printator company in Berlin, and presented the idea to Rudolf Hell at his lab on November 24th. The tape had to be pulled through the Hellschreiber printer (the modified Hell Morse practice recorder mentioned above) by hand. During his visit, Lohmann requested Hell to build a Printator-tape Hellschreiber printer; Hell confirmed receipt of the request the same day in writing. Nothing happened until spring of 1938. Then, Telefunken made three decisions: 1) The beacon printer is to have 2x2 parallel printer traces, for simultaneous printing of two beacons (triangulation); 2) A beacon identifier letter is to be added to the bearing/azimuth Hellschreiber symbology transmission; 3) Presentation of the printed paper tape to the operator has to be adapted to the conditions on-board the aircraft. The printing method was now finalized, with exception of the decision whether or not to use Printator tape.

Due to lack of time and resources, there was no development activity around the Hellschreiber beacon printer at the Hell Co. until the fall of 1938, when they finally build a 2x2 channel paper tape printer. See Fig. 6. System tests were successful, as was a demo flight with the RLM during which triangulation of two beacons was shown.


Bernhardine time-line patents

Fig. 6: Evolution of "Bernhardine" printers - system concept validation and tests

(sources: ref. 181, 183; all three are roll chart recorders).

Both Rudolf Hell and Telefunken's aeronautical navigation departments (Luftnavigation, LN 3 and 4) continued to decline testing Lohmann's persistent hobby-horse: Printator tape. Then, at a different Telefunken department, Lohmann had Mr Lehmpull make design drawings for a Hellschreiber "Printator printer", and a prototype was built in October of 1938. It was tested during the winter of 1938/39. The printer comprised an infinite loop of Printator tape that was wide enough for two Hellschreiber printer mechanisms. The tape was mounted on a drum that included knife blades for separating the tape layers. Telefunken/Lohmann patented this Printator drum printer in March of 1939 (patent 767513). It claimed the advantage that the erasable tape obviated the need for replacing a used roll of paper tape while in flight. During the spring of 1939, Lohmann demonstrated the Printator drum printer to Rudolf Hell. Hell still declines designing a Printator Hellschreiber printer, due to lack of time/resources and other unspecified  considerations. In order to drum up support, Lohmann also demonstrated a Printator tape printer to the RLM.

Also during the spring of 1939, the RLM decided  to proceed and implement the system. However, they put the program on hold, as the scope of the development program was considered to large for the anticipated short duration of the forthcoming war. Nevertheless, the system (with UHF beacons) was developed up to pre-production maturity by the summer of 1940. This included a new 2x2 channel paper tape Hellschreiber (see Fig. 6). This 2x2 channel printer was the last pre-production model before the similar looking first series-production model, the 2-channel HS 120. They also upgraded the printer amplifier. It now included automatic start/stop of the printer motor based on received signal strength (to save paper tape; ref. Telefunken/Lohmann patent 767527), and generation of Automatic Gain Control for the beacon receiver.

During the spring of 1940, the RLM suddenly issued a contract to Telefunken for final development of the rotating beacon system ( = beacon ground station + airborne equipment with printer). Telefunken and its AEG-partner Siemens & Halske (S&H) decided that it was S&H who should develop the Printator drum printer to production readiness, under contract to Telefunken. Note that S&H was the manufacturer of the portable military Hell Feldfernschreiber and the Presse Hell printers for news agencies. Telefunken showed its prototype Printator drum Hellschreiber printer to S&H mid-April of 1940. During the following month, Telefunken and S&H also discussed development of the (rather simple) 2-tone filter unit by S&H.

Mid-May 1940, Telefunken shows design drawings of a new Printator printer embodiment to S&H. Instead of the infinite loop of Printator tape in the drum printer, the print medium is now a Printator foil disk. The drum approach had to be abandoned due to two serious problems, as explained in the October 1940 Telefunken/Lohmann patent for the disk printer (patent 767536): 1) unavoidable imperfections in the drum surface (bumps, seams, out-of-round tolerances) cause tape ruptures, and, therefore, 2) spare "drum + tape" modules would have to be carried in the aircraft.

As a rather interesting side note, the RLM informed Telefunken early October 1940 that the disk printer and associated 2-channel audio filter unit were to be developed with special RLM priority, as an improved cockpit instrument for use with the "Knickebein" beam system (ref. 204A, 204F)! By that time, the British had deployed over a dozen high-power jamming transmitters as a Knickebein countermeasure. As Knickebein had the British codename "Headache", their codename for the jammers was "Aspirin". The German codename for the new airborne equipment set ("Flugzeug-Bordanlage") was "Ulrich". However, it appears this airborne printer system was never implemented...

Six months later, in the April-May 1941 time-frame, the RLM ordered 2000 Hellschreiber paper-tape printers directly from the Hell Co. I.e., they were not Printator foil printers, as, most likely, those were not yet deemed mature enough. As the airborne printer equipment set had the designator FuG 120 (codename "Bernhardine"), this Hellschreiber received the designator HS 120, see Fig. 7 below. The HS 120 was first used during system tests at the "Bernhard" beacon Be-0 near Berlin in September of 1941. It is a reel-to-reel recorder, like the models that were used during the pre-production development phase (Fig. 6 above).The RLM ordered the associated 2-channel tone filter unit directly from S&H.


Bernhardine time-line patents

Fig. 7: Evolution of "Bernhardine" printers - series production

(sources: ref. 181, 183)

Note that during May of 1941, the sales department of Telefunken managed to change the mind of the RLM, and Telefunken became prime contractor to the RLM for the design, development, and series production of the entire "Bernhard/Bernhardine" program. Originally, the RLM awarded the design and development contract for  the printer to the Hell Co., and for the audio filter to S&H. During June of 1941, Telefunken provided a 2-channel Hellschreiber printer amplifier to S&H. Several times throughout that month, they also made printer system test equipment available to S&H. Also in June, S&H built a Printator disk printer that met Telefunken and RLM wishes.

Subsequently, in August of 1941, S&H received an order from Telefunken for the production of 2400 DFS 120 Printator foil-disk printers. At least the first 2000 of these were to be supplied to the RLM by Telefunken, with S&H as the manufacturer (i.e., as subcontractor to Telefunken). It is unclear if the original RLM order placed at the Hell Co. for 2000 HS 120 printers was maintained, or modified to a smaller quantity.

Starting around 1942, the available references (204A-204R) generally refer to the FuG 120 "Bernhardine" printer as Drehfunkschreiber (lit.: rotating beacon printer) DFS 120, in particular in reference to the Printator-foil based Peilschreiber (lit.: direction finding printer) Psch 120. Ref. 204M even double-dips with "Peilschreiber DFS 120".

Per ref. 181, the Printator disk-printer was considered "production ready" by October of 1942, at which time the HS 120 was considered "provisional". Ref. 181 also shows a photo (Fig. 61 below) of a mature prototype disk-printer. This confirms that at that time, the final Psch 120 design (in particular the housing with control knob and connector on the side - see Fig. 62) was not yet available. Fig. 8 below shows an RLM / Ln outline drawing for the disk-printer that is dated December 1942. However, ref. 183 (from July 1943!) states that the Printator-disk printer was expected to become the standard for practical (operational) use, whereas the HS 120 was (or had become) more suitable for training purposes and testing (incl. transmission monitoring at each Bernhard beacon). This implies that at least until mid-1943, their had been very significant problems with the Printator-disk printer: it was either still not "production ready", had encountered manufacturing issues, or was not suitable for operational use. This is corroborated by the available photos of the FuG 120 system test rack: in October 1942 (ref. 181) and July 1943 (ref. 183), the rack only has an HS 120, but in July 1944 (ref. 203), it has both an HS 120 and a Psch 120a.

Note that ref. 44 (based on RLM and LN documents) states that both the HS 120 and the Psch 120 were series-built in 1942. This may explain the development, production, and operational use of a paper-tape DFS 120 / Psch 120. In ref. 199 (unfortunately undated), it is marked that this paper-tape Psch 120 was supplied to the RLM by S&H WWT ("Wernerwerk Telegrafen-Abt."). This is the middle printer shown in Fig. 7 above. Most likely (no reason why not), it was form-fit-function compatible and fully interchangeable with the foil-disk Psch 120. Ref. 3 states that the paper-tape Psch 120 entered into service first, was then replaced by the Printator foil-disk Psch 120, and when the latter proved unsuitable for operational use, the aircraft were retrofitted back to the paper-tape Psch 120. However, ref. 3 also states that series-production of the FuG 120 "Bernhardine" system (which implies the HS 120) did not start until 1943, which contradicts ref. 44 (unless ref. 3 actually meant FuG 120a or FuG120b...)

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 somehow involved with the Psch 120(a) printer (ref. 54). A number of development labs (some 600-700 employees, no production) were moved there in August of 1943, from Lorenz in Berlin (ref. 55).

As discussed above, a distinction is made between the HS 120 Hellschreiber, and the DFS 120 / Psch 120 bearing printers (which, of course, are also Hellschreiber printers). However, there is considerable confusion about the use of the designators Psch 120 versus Psch 120a. Some of the original German WW2 documents use Psch 120 for the compact paper tape bearing printer, and Psch 120a for the bearing printer with an erasable Printator foil-disk. However, other WW2 documents use Psch 120a for the paper tape printer. This is illustrated in the outline drawings of Fig. 8, where both tape and disk printer are designated Psch 120a - with exactly the same Luftnachrichten reference number (Ln 28997) and Gerät Nummer drawing number (124-270A)! Perhaps this unusual confusion is related to the Psch 120 and the Psch 120a being interchangeable regarding electromechanical interfaces, and also because the foil-disk printer at some point in time replaced the paper tape printer, but proved unreliable and impractical, and was shortly thereafter retrofitted back to the paper tape printer (ref. 2).

Bernhardine Psch 120 120a

Fig. 8: Both paper tape printer and Printator foil-disk printer designated as "Psch 120 a"

(sources: ref. 199, 212)

Bernhardine Psch 120 120a

Fig. 9: HS 120 printer and Printator foil-disk printer designated as "Psch 120 a"

(sources: ref. Fig. 10 in ref. 203)

Other examples from literature:

  • Ref. 212 from 1944 (p. 348) shows the outline drawing of Printator foil-disk printer marked P.Sch. 120A, see Fig. 8 above.
  • Ref. 198A (1944) states that the FuG 120 "Bernhardine" system included the HS 120 printer, whereas the FuG 120a included the Psch 120a printer. It also states that paper tape came out of the latter printer: "...papierstreifen verlässt den Peilschreiber lose..." This implies that the referenced Psch 120a was a paper tape printer.
  • Ref. 203 (p. 4 of 10, 1944) shows a photo of a PGst 120 test rack with a foil-disk printer that is labeled Psch 120a, see Fig. 9 above.
  • Ref. 44 lists the Psch 120A (Ln 28997, Gerätnr. 124-270 A) and matching bearing printer paper tape container ("Papierbehälter für Peilschreiber", Ln 28999, Gerätnr. 24-273A), which suggests that the Psch 120A uses paper tape.

A similar confusion exists regarding the version(s) of the FuG 120 that corresponded to the Psch 120 and Psch 120a. The FuG 120 - without version suffix - was the first generation, and included the HS 120 printer. Intuitively, it would be logical that the next version of the FuG 120 would be the FuG 120a, and included the Psch 120. Likewise, FuG 120b, would have succeeded FuG 120a, and included the Psch 120a. This is also claimed in ref. 2 and 3. However, WW2 documents available to me, only mention FuG 120a with a Psch 120a... (e.g., ref. 198A & 198B). There appears to be no confusion about the FuG 120k including the small ("klein") simplified Psch 120k (which actually never entered operational service).

In the remainder of this page, Psch 120 is used exclusively for the compact paper tape bearing printer, and Psch 120a for the bearing printer with an erasable Printator foil-disk. Caveat emptor!


"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 10. 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.

Standard 1-channel Hellschreiber printer

Fig. 4: 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).

2-channel Bernhardine Hellschreiber printer

Fig. 11: 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 7). 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.

azimuth print-out

Fig. 12: Compass scale print-out with azimuth value and station identifier letter

(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. 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 13 and 14. The azimuth printer has a 3-start spindle: N = 3. Its three thread-segments each cover 360° / 3 = 120° of the spindle hub. Again, thread segments do not overlap. 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 revolution, the 6-start spindle prints twice as many.

6- and 3-start spindles
print of 6- and 3-start spindle

Fig. 13: The 6-start spindle (bar-graph) and 3-start spindle (azimuth) of the "Bernhardine" Hellschreiber printers


azimuth print-out

Fig. 14: The spindles of an HS120 "Bernhardine" Hellschreiber printer

(source left-hand photo: ©2010 Leonard Hunter, used with permission; photo of shaft with both spindles: Fig. 52 in ref. 181)

The columns of the bar-graph must 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 revolution 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 13 and 14 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. The "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. Possibly it is dark blue, as in Fig. 98. I have tried to contact the company several times by email and conventional mail, always without success...



HELLSCHREIBER PRINTER-CHANNEL FOR SIGNAL-STRENGTH

As described above, the "Bernhard" beacon 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 printer trace. See Figures 3, 15, and 16. The bar-graph has six bars per degree of azimuth (ref. 15, 181). 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%).

Berhard signal strength plot

Fig. 15: Signal-level bar-graph based on received signal strength from the main lobes of the antenna pattern

(source: adapted from ref. 46)

Berhard signal strength plot

Fig. 16: Signal strength bars, as printed with the Bernhardine-Hellschreiber

(source: ref. 3)

The height of each printed bar must correspond to the (limited) signal strength at that moment. In 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 momentary amplitude of the received signal must be converted to the width of an energization pulse. This Pulse Width Modulation 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 17. The concept of this Pulse Width Modulation conversion was conceived by Rudolf Hell, and patented by him in October of 1937 (patent 730625). The actual Pulse Width Modulator circuitry was located in the SV 120 printer amplifier.

SV120 pulse-width-modulator

Fig. 17: 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 voltage is then offset with a fixed negative grid-bias voltage (20). The latter voltage is chosen such that if the input signal is zero ( = no beacon signal received), 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!

SV120 pulse-width-modulator

Fig. 18: 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. The notched disk and associated contact ("Nockenkontaktsatz") was made by the Hell company (p. 33 in ref. 15).

SV120 pulse-width-modulator

Fig. 19: Plot of the actual pulse-width (h1 - h5) for a linearly increasing input-signal amplitude

(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 "Bernhardine" Hellschreiber-printer channel, directly below the bar graph of the signal-strength. As the beacon rotates at 12°/sec, the beacon signals are only received for a couple of seconds during each rotation. The result is a printed segment of the 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 21).

Patin remote compass

Fig. 20: Remote compass, as used e.g. in Fw190

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

":Bernhardine" compass card

Fig. 21: The compass scale 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" beacon, 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 (for a standard Hellschreiber bottom-up printer spindle):

Downward slant

Fig. 22: 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 23.

Split text line

Fig. 23: 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 (or, equivalently, a two-start spindle with two intertwined 1-turn threads). 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 24. This is combined with manual adjustment of the printer's motor speed.

Double text line

Fig. 24: Double-line text remains completely legible despite slant caused by speed difference


Double etxt line

Fig. 25: Double-line text remains completely legible despite shift caused by phase difference


This solution is not an option for the "Bernhardine" printer! Yes, doubling the printout of the azimuth data would make the compass data legible at all time. However, due to the slant or vertical shift of the printed azimuth data, the bar-graph pointer would no longer line up with the degree tick-marks. See Figure 26. 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 always be printed just below, and parallel to the bar-graph.

No double-helix for Bernhardine

Fig. 26: 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" printer motor runs a little faster than the nominal speed: 1-2% (p. 91 in ref. 181, 1.5% per ref. 15 and p. 18 in ref. 183). The 1-2% is equivalent to about ½ pixel per three pixel-columns that make up each 1 degree compass interval: 1-2% x 3 columns x 12 pixels/column = 0.36 - 0.72 pixels. This way, it finishes printing each set of three pixel columns slightly early: nominal pixel duration is 30 sec/revolution / (360° x 3 columns/° x 12 pixels/column) = 2.31 msec (p. 91 in ref. 181 incorrectly states "ca. 30 msec", which is actually the 27.78 msec nominal duration of one pixel column). The printer then waits a brief moment until the next sync pulse (here: a tick-mark) is detected, and then starts to print the next character at exactly the right moment. The same method has been used since the mid-1950s, to synchronize clocks at train stations to an accurate central master clock: each minute, all station clocks run several seconds fast (1.5 sec nominally). 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 at exactly the right moment.

To make this synchronization scheme work, at least the 1.5 pixels preceding each "degree" tick-mark (i.e., at the bottom of the preceding pixel column) must be white. This minimum pause is equal to 1.5 pixel / (3 x 12 pixels) ≈ 4% of the transmission duration of 1 degree. This is just large enough to accommodate several factors:

  • Tolerances in the rotational speed of the "Bernhard" beacon: it was regulated to within ±0.2-0.3 % of exactly 2 rpm (p. 80 in ref. 181, p. 8 & 18 in ref. 183).
  • The beacon should not turn slower than the allowed tolerance. 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 of the printed symbology 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.
  • Tolerances in the printer motor speed: it was regulated to within ±0.5 % with a centrifugal regulator.
  • The reaction speed of the spring-loaded "catch and release" synchronization electro-magnet.
  • The 2400 Hz tone used for the Hellschreiber pulses has a cycle time of 1000 / 2400 ≈ 0.4 msec. The pulse-detection circuitry that drives the electro-magnet always loses part of one tone-cycle, both at the start and at the end of each pulse.

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 cannot be 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. 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.

Let's go through a complete "catch-and-release"" sequence, see Figure 27. 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).

Bernhardine sync mechanism

Fig. 27: Complete cycle of the synchronization process

(source: adapted from Figure 9d of ref. 15)

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 18 (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.

Wavy azimuth track

Fig. 28: Print-out of the test beacon "M" at Mietgendorf - with wavy azimuth track

(source: Fig. 27 in ref 181, also used in 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 29 shows how it had to be used to obtain correct printing quality.

Wavy azimuth track

Fig. 29: Incorrect and correct printing - adjustment with manual gain control on the HS120 printer

(source: figure 25 in ref. 15, ref. 48)

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 added a degree tick-mark at the top of every single pixel-column, instead of every third column (p. 4 ( = Blatt 3) of ref. 198A).


"BERNHARDINE" PRINTER MODEL "HS 120"

The "Spezial Hellschreiber HS 120" printer of the FuG 120 "Bernhardine" system was designed and built by the Rudolf Hell company in Berlin. It comprises the following principal components, see Figure 30:

  • 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,
  • potentiometer 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.

principle diagram HS120

Fig. 30: Principle diagram of the HS 120 dual Hellschreiber printer


The same basic design applies to the Psch120, and DFS120/Psch120a.

I have documented three HS 120 Hellschreiber machines: one in the collection of the Imperial War Museums in the UK (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) and ref. 212 state 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. 31). 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 stationary equipment room of every "Bernhard" beacon.

HS120 front view

Fig. 31: Front view of an HS120 Hellschreiber - protective cover down

(printer with Werk-Nr. 70206; IWM catalog nr. COM 493, photo used in accordance with ref. 169)

HS120 front view

Fig. 32: Front view of an HS120 Hellschreiber - protective cover up

(printer with Werk-Nr. 70206; IWM catalog nr. COM 493, 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 (see Fig. 40 below).

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:

HS120 front view

Fig. 33: 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.

HS120 front view

Fig. 34: 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)

HS120 front view

Fig. 35: 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:

HS120 front view

Fig. 36: 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:

Label on HS120

Fig. 37: 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.

Label on HS120

Fig. 38: 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:

BAL378 on HS120

Fig. 39: "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)

BAL 378 number has also appeared on products of Fernmeldetechnisches Entwicklungslaboratorium Dr. Ing. H. Kimmel ("Development lab for telecom equipment") in Munich, later Münchener Apparatebau für Elektronische Geräte Kimmel GmbH & Co. KG. 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.

HS120

Fig. 40: HS120 Hellschreiber - housing removed, top of front panel flipped down

(source: Figure 14 in ref. 203; similar: Figure 8 in ref. 183)

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:

HS120 top view

Fig. 41 Top-view of the inside of an HS120 with Werk-Nr. 70346

(original unedited photo: ©2010 L. Hunter, used with permission)


HS120

Fig. 42: Top-view diagram of an HS120 Hellschreiber

(source: adapted from Figure 13 in ref. 15)

HS120

Fig. 43: The plug-in printer module of the HS120 Hellschreiber

(source: Figure 52 in ref. 181)

6-start HS120 spindle

Fig. 44: 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 beacon 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.

HS120 rear view

Fig. 45: Rear-view of the HS120 Hellschreiber

(source: Fig. 15 in ref. 200)

The HS120 is powered by a 24 Volt DC motor, running at 3000 rpm. It was a model SMK0, 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.

Label on Stark-Motor

Fig. 46: Label on the motor - 24VDC, 12 watt, 3000 rpm

(Motor type "SMK0", as specified in ref. 15)

The company was owned by Hans Stark:

Hans Stark phone book entry 1943

Fig. 47: Listing in the electric motor section of the 1943 Berlin phonebook (Teil II, p. 165)

(with advert for "small rpm-controlled electric machines"

XXXXX

Fig. 48: Listing in the electric motor section of the 1951 Berlin phonebook

(still at the same address as in 1943)

Right-hand sode of an HS120

Fig. 49: Right-hand side of an HS120 Hellschreiber - Werk-Nr. unknown

(two stacked felt ink rollers left of center; synchronization mechanism for the upper printer channel removed, adapted to 2 narrow tapes)

The bottom of the HS 120 shows how the single motor drives the shaft of the printer spindles and the paper tape transport (Figure 50). All capacitors and inductors are also located here. The spool for the printed paper tape is driven via a spring belt that can slip (top right in Figure 50); this tensioning mechanism is needed, as the speed of the spool depends on how much paper tape is wound onto it.

HS120 bottom view

Fig. 50: Bottom of the HS120 Hellschreiber

(original photo: ©2010 Leonard Hunter, used with permission)

HS120

Fig. 51: 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), "Deutsches Reichspatentamt" (the patent office), and angemeldet: "applied for" ("pending"). This implies "registration without patent protection".

BAJANZ marking inside HS120

Fig. 52: Marking of the manufacturer of the Plexiglas front panel



"BERNHARDINE" PRINTER MODEL "Psch 120"

The paper-tape Psch 120 "Peilschreiber" (bearing printer) was built by Siemens & Halske A.-G in Berlin (p. 188 in ref. 44, ref. 212). Their military manufacturer code was "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.

Psch 120

Fig. 53: Peilschreiber (bearing printer) "Psch 120" of the FuG 120a - a compact paper tape printer

(source: Figure 2 & 3 in ref. 198A)

Psch 120

Fig. 54: Photo of another "Psch120" unit - without cover for gearing of the paper tape transportation drive

(source: ref. 7B)

Psch 120

Fig. 55: Reglerkasten (control box) "RgK 120a" of the Psch 120a

(source: Figure 5 in ref. 198A)

Ref. 198A, 199 - differences between the FuG 120 with Hellschreiber HS 120 and the FuG 120a with the Peilschreiber Psch 120 (paper tape printer):

  • Size of the Psch 120 is 18x12.2x15.3 cm (WxHxD, ≈7x5x6"), about half that of HS 120, as is the weight (3.8 kg).
  • Psch 120 has no spool for winding up printed tape; printed tape exits the printer; a sharp edge is provided to tear off the tape.
  • Psch 120 does not have a "Hell-Dunkel" bright-dim toggle switch, but a potentiometer for continuous variation of the lighting.
  • The "D" button of the Psch 120 not only resets the AGC voltage to the EBl 3 receiver, but also turns on the motor to advance the paper tape (e.g., to exit a section of printed tape that is visible in the viewing window and pass it on to another crew member).
  • The automatic start/stop function of the motor now has a delayed "off", such that the printed section of the tape automatically leaves the machine.
  • The pointer spindle no longer has 6 but only 4 starts (threads). I.e., it only prints 4 pixel-columns per revolution of the spindle. The cam wheel involved with generating the required sawtooth signal also only has 4 notches instead of six (one per spindle-start). This causes the amplitude of the generated sawtooth signal to be reduced. To compensate, the associated Pulse Width Modulation circuitry in the Schreibverstärker SV 120 printer-amplifier was modified to increase gain.
  • The compass scale Hell-printer still has 3-starts, but the synchronization catch has been moved away from immediately next to the spindle. In the HS 120, the spindle for printing the compass scale (or command message) can spin freely on the printer spindle shaft, and is held by a slip clutch. The Psch 120 drawing (Fig. 56 below) suggests that entire spindle shaft (i.e., both spindles) downstream of the slip clutch (item nr. 366) are held & released by the synch mechanism (notched disk, item nr. 302, and synchronization e-magnet, item nr. 336).
  • The "Empfindlichkeit" sensitivity gain control of the HS 120 has been moved to a small external control box, the Reglerkasten RgK 120a (Fig. 55).
  • The electro-magnets of the Psch 120 printer require a nominal DC current of 32 mA, compared to 40 mA in the HS 120 printer. Therefore, the RgK 120a control box also contains current-limiting resistors. Furthermore, the RgK 120a has a toggle switch, to turn the power control relay of the Umformer U 120 power supply on/off.
  • Like the HS 120, the 24 volt DC motor has a centrifugal speed regulator. However, the associated electrical contact is now stationary.
  • The printer has a die-cast housing ("Spritzguß") instead of sheet metal. The HS 120 does not have a mounting frame with shock mounts, but just four shock mounts.
  • The associated mounting frame is  RPsch 120a, with 3 captive screws.
  • System accuracy: +/- 0.5 deg, as with the HS 120.
  • The paper tape of the HS 120 is over 4 cm wide. The paper tape of the Psch 120 is about 3 cm wide (based on its relative size in Fig. 53 & 54.

Note that the above differences with respect to the HS 120 also apply to the Printator foil-disk printer Psch 120a.

The unit measured 18x18.5x12.2 cm (WxDxH, ≈7x7.3x5 inch; excluding the protruding connector block) and weighed 3.8 kg (8.4 lbs); ref. 199). A roll of paper lasted 8 printing hours.

Psch 120

Fig. 56: The printer mechanism of the "Psch120" paper tape printer

(source: ref. 198A)


"BERNHARDINE" PRINTER MODEL "DFS 120" / "Psch 120A"

Peilschreiber 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 Telefunken/Lohmann 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. The tape was referred to as "Printator" tape. In 1928, Hugo Hahn, owner of the Printator G.m.b.H. company in Berlin-Weißensee (Lehderstraße 20-21), patented a 3-layer writing pad with a built-in layer-separation mechanism (US patent nr. 1,891,414 "Writing and drawing pad"). Hahn also held several patents related to stamping, and also one from 1925 for boots with built-in support soles for people with flat feet ("Plattfußstiefel").

The underlying erasable 3-layer technology actually dates back to April of 1920, when Daniel Evans of Highbury, London, England filed a patent for a quick-erase "Writing and Drawing Surface" pad. He received U.S. patent no. 1455579 in May of 1923. The original commercial implementation consisted of a piece of black waxed cardboard and a translucent grey plastic sheet. One would write or draw on it with a blunt plastic stylus, not unlike writing on a modern Personal Digital Assistants (PDAs). Over the years, it became world famous as the "Magic Slate" (a.k.a. magic board, mystic pad; in Germany: Printator, Wunderblock, Zaubertafel, Notizlöschblock; in France: écran magique, bloc chimique perpétuel; in Italian: lavagna magica). Some sources suggest that this pad was patented (or even invented) in 1923, by R.A. Watkins of Illinois/USA (later Watkins-Strathmore Co, until acquired by Western Publishing Co. in 1957). However, there is no trace of such a patent by Mr Watkins in worldwide patent databases...

Magic Slate

Fig. 57: A "Magic Slate" note pad or doodle pad

(source patent drawings: U.S. patent no. 1455579)

In the Telefunken/Lohmann patent 767513, there are two embodiments of a Printator Hellschreiber printer. In the second one, a section of Printator tape is mounted on a cylindrical "drum". 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 (pixels) 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 58. This is referred to as a "Wachsschreiber" or "Folienschreiber", i.e., a wax or foil (film) printer. In the USA, one can rather easily patent pre-existing devices, methods, plants, etc., so the Bernhardine Wachsschreiber was (re-)patented there in 2003 (US Patent 6,578,615) by the Hewlett-Packard (HP) company.

Erasable wax printer

Fig. 58: Concept of a "Bernhardine" erasable Printator-tape drum printer

(source: adapted from Figure 3 and 4 in patent 767513)

Whereas patent 767513 proposes an endless tape, the 1940 Telefunken/Lohmann patent 767536 proposes a triple-layer erasable disk. See Figure 59. 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) unavoidable imperfections in the drum surface (bumps, seams, out-of-round tolerances) cause tape ruptures, and, therefore, 2) spare "drum + tape" modules would have to be carried in the aircraft.

Erasable wx printer disk

Fig. 59: Erasable-disk "Bernhardine" Printator-foil printer

(source: adapted from Reichspatent Nr. 767536 , see patent table below)

Printator

Fig. 60: Entries in the Berlin phonebook and a 1941 Luftwaffe "Notizlöschbuch" of navigation practice set made by Printator

(source: Berliner Adreßbuch 1941 & 1943, Amtliches Fernsprechbuch 1941; Navigations-Lehr- und Übungsgerät, 1941)

Supposedly the erasable disk concept corrected these shortcomings. This is what was actually implemented in the Psch 120a "Bernhardine" printer. See Figure 61 and 62. It has the same shape and size as the Psch 120 paper-tape printer. Clearly, replacing an erasable disk module might not necessarily have been any easier than replacing a drum or installing a new tape. The disk printer proved inadequate in operation: too complicated and unreliable. It was taken out of service, and retrofitted back to the Psch 120 paper-tape printer (p. 96 in ref. 3).

Psch120a printer

Fig. 61: Prototype Nr. 2 Peilschreiber "Psch 120a" of FuG 120b - an erasable disk printer

(source: Fig.40 in ref. 181, October 1942)

The equipment label on the above Psch 120a reads Siemens & Halske, Peilschreiber, Werk Nr. - Muster 2 (bearing printer,  prototype number 2 ).

Psch120a printer

Fig. 62: 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)

The housing measures 17.9x11.3x15.3cm (WxHxD, 7x4.4x6.4 inch). The unit weighs 3.5 kg (≈7.7 lbs). Ref. 212.

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, but generated by a PS 120 test signal generator. Also, the station identifier is "D+" or "DT", rather than the standard single letter. 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.

Psch120 print out

Fig. 63: Close-up of the Printator foil disk in the PSch 120a in Fig. 62



THE PRINTER OF "BERNHARDINE" FuG 120k

Towards the end of the war, a much simplified Bernhard/Bernhardine system was conceived, and possibly even 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. The printer-amplifier unit also only had one channel. Hence, the actual printer only had a single printer mechanism, printed on narrower paper tape, and had no cam wheel on the spindle shaft as part of the synchronization circuitry. 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 64. Clearly, the operator had to do some interpolation. 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).

High accuracy Bernhardine

Fig. 64: Separate signal-strength bar graph and azimuth scale - high accuracy


Reduced accuracy Bernhardine

Fig. 65: Azimuth data transmitted via the twin-lobe antenna system - reduced accuracy


This approach also implies a simplification of the Bernhard ground station: only one transmitter is needed, and the single-lobe antenna array is no longer needed. Note that this concept is already mentioned in the original 1936 Lohmann/Telefunken main patent 767354 and more explicitly covered by the Telefunken/Herbert Muth patent  767919 of December 1940.

No photos, diagrams, or other documentations of this printer model are available. It does not appear that this printer, and the associated modified "Bernhard" ground station modification, ever went into service.


PRINTER AMPLIFIER SV 120 (SCHREIBVERSTÄRKER)

The 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 66). It converts received tone-pulses into energization pulses for the electro-magnets of the printer. The audio input signal is amplified, band-pass filtered, rectified. A final amplifier acts as a power-switch.

Hellschreiber printer-driver basic schematic

Fig. 66: Simplified principle diagram of a standard Hellschreiber printer-amplifier channel


However, the SV 120 is much more than just two such channels - see Figure 69. 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).

SV 120 tubes

Fig. 67: SV120 tubes RV12P2000, LV1, and LG6 (to the same scale)


SV 120

Fig. 68: The SV 120 printer amplifier

(source: Fig. 10 and 11 in ref. 200; note the hinged cover on the three rectifiers, one is flipped down)

SV120 diagram

Fig. 69: 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.

FuG120 pre-amp filter channel

Fig. 70: 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 71:

  • 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 above.

FuG120 bar-graph channel

Fig. 71: 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 72:

  • 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.
FuG120 azim channel

Fig. 72: 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.


FILTER UNIT SG 120 (SIEBGERÄT)

The "Bernhard" navigation beacon has two AM transmitters. Their carrier frequencies were spaced 10 kHz (±1 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 was 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 73. 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.

RF and audio spectra

Fig. 73: Nominal RF spectrum of the "Bernhard" transmitter outputs

(source: frequencies taken from ref. 15, ref. 181)

The FuG120 "Bernhardine" is operated in combination with an EBL3 shortwave AM navigation receiver. The audio output of the EBL3 contains both the constant 1800 Hz tone from the "Bernhard" beacon's twin-lobe beam, the 2600 Hz Hellschreiber tone pulses that represent the azimuth symbology, and the 9-11 kHz (10 kHz nominal) difference between the carrier frequencies of the two "Bernhard" transmitters, ref. 15 (p. 10 = pdf p. 11):

RF and audio spectra

Fig. 74: 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 ("Siebgerät") audio filter unit. This unit has the Luftwaffe Gerät-Nummer 124-977-A (ref. 15). The unit measures 22.5x16.7x9.3 cm (WxHxD, ≈ 9x6.6x3.7 inch) and weighs about 7 kg (≈ 15.5 lbs); ref. 15, 212.

SG120 block diagram

Fig. 75: The SG120 2-channel audio filter unit - cover removed

(source: Fig. 12 in ref. 200; the three large metal-shielded boxes contain the seven inductor coils)

SG120 block diagram

Fig. 76: Block-diagram of the SG120 2-channel audio filter unit

(source: adapted from ref. 15)

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 (ref. 15) only list the values of all the capacitors, but not of the seven inductors. So the actual filter characteristics can not be reconstructed (unless an intact SV120 unit is found).

RF and audio spectra

Fig. 77: Audio spectrum of the two SG 120 filter-channel outputs


The two separate tone 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. A mode switch controls the UG 120 switching unit. The UG 120 was built by Telefunken (ref. 44, 212). It measures 22.2x20x4 cm (WxDxH, ≈9x8x1.6 inch) and weighs about 0.5 kg (≈1.1 lbs).

This unit is basically a small box with a 4P2T relay (4 sets of changeover contacts):

UG120

Fig. 78: Umschaltgerät UG 120 - switch-box

(source: Fig. 16 and 17 in ref. 200)

UG120 diagram

Fig. 79: Principle diagram of the UG 120 switching unit

(source: adapted from Figure-7 and Appendix-e in ref. 15)

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.

The re-configuration is done with the SpKf 1a mode switch. This is a modified SpKf 1 "Sprechknopf" switch. The latter is used to switch a microphone on and off, like a push-to-talk switch (PTT). SpKf 1 has switch positions that are labeled "EIN" (on) and ""AUS" (off). Model 1a is a 3-position switch. A white pushbutton enables changing the switch position. The center position is labeled "NFF" ("Navigationsfunkfeuer" = Navigation Beacon). The left & right position are labeled "LFF" ("Landefunkfeuer" = Landing Beacon). 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.

SpKf1a

Fig. 80: The 3-position SpKf1a switch



SpKf1a

Fig. 81: The SpKf1a switch - manufactured by Frieseke & Höpfner

(source: ref. 44)


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). The switch measures 3.5x3.7x5 cm (WxHxD, ≈1.4x1.5x2 inch inch) and weighs 40 grams (1.4 oz.); ref. 212.


F&H letterhead

Fig. 82: Letterhead of the Frieseke & Höpfner company (1945)



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 normal charging voltage for 24 VDC lead-acid batteries, like 13.8 is for 12 VDC lead-acid 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 unit measures 34.2x22.5x16.4 cm (WxHxD, ≈13x9x6.5 inch) and weighs about 12 kg (≈26.5 lbs); ref. 15, 212.

U120 diagram

Fig. 83: The U 120 power supply - cover removed

(source: Fig. 23 in ref. 200)

The U120 has five outputs. They 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.

U120 diagram

Fig. 84: 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 secondary voltages 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.

U120 diagram

Fig. 85: LG6 tube and Metall Stabilovolt M STV 140/60 Z tube (without extraction knob)



FuG 120 EQUIPMENT MOUNTING FRAMES

The FuG 120 system comprised the following mounting frames:

  • RPsch 120a, Rahmen für Peilschreiber: mounting frame for a Psch 120(a)bearing printer,
  • This is the same as the 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.

As shown in Fig. 86 below, the HS 120 printer was not mounted on a frame: the four lugs on the back of the HS 120 were mounted directly onto four shock mounts, to mechanically isolate the printer from shocks and vibration.

The FuG 120 "Bernhardine" system includes the following interconnection items (incl. for connections with the FuBl 2 beacon receiver radio system):

  • ZLK VIII S 3, Zwischenleitungskupplung: splitter/coupler unit.
  • VD 120, Verteilerdose: junction box,
  • Eight custom cables (including connectors), with the following number ("Leitung-Nummer"), ref. 15:
  • 371F, 372F (1 conductor),
  • 373F, 378F (12 conductors),
  • 374F - 376F (8 conductors),
  • 377F (2 conductors).

The FuG 120 system test rack includes all of the mounting frames and interconnect items listed above, as well as test rack specific cables ("Prüftafel-Verbindungsleitung", "Hellschreiber-Prüfleitung"):

FuG 120 frames

Fig. 86: Prüfgestell PGst 120 without equipment set, front & back (1944)

(source: combination of Fig. 9 and 11 in ref. 203)

The test rack was made by Telefunken, measures 58x82 cm (WxH, ≈23x32 inch), and weighs about 22 kg (≈49 lbs), ref. 212. Note that through 1943 (ref. 181, 183), the test rack only accommodated an HS 120 printer, but the 1944 rack both an HS 120 and a Psch 120 printer (ref. 203):


FuG 120 frames

Fig. 87: Prüfgestell PGst 120 - FuG 120 system test rack with equipment set

(sources: Fig. 39 in ref. 181 ( = Fig. 6 in ref. 183), Fig. 10 in ref. 203)


The mounting from for the The RPSch 120a (also written as RP.Sch.120A) is the mounting frame for the PSch120(a) "Peilschreiber". The frame measured 16.7x18.6 cm (≈6.6x7.3 inch) and weighed about 320 gram (≈0.7 lbs); ref. 212. It has 4 shock mounts.

FuG 120 frames

Fig. 88: RPsch 120a - mounting frame for the Psch 120(a) printer (same as RDFS 120)

(source: Fig. 4 in ref. 189A)

FuG 120 frames

Fig. 89: Top and bottom of an RPsch 120a

(source: eBay)

FuG 120 frames

Fig. 90: Label and manufacturer markings on the above RPsch 120a

(source: eBay art. nr. 201963118195)


The metal frame of the RPSch 120a was manufactured for Siemens & Halske AG by the Nürnberger Aluminiumwerke GmbH, tradename Nüral (esp. for engine pistons). This company was founded in 1924. In 1962, it merged with Aluminiumwerke Göttingen GmbH, to form Alcan Aluminiumwerke GmbH. During the 1990s, it was absorbed into US-based Federal-Mogul company. Ref. 213.

Feld-Hell

Fig. 91: advertising for Nüral die-cast engine blocks and pistons  (1940 and 1947)


In the three mounting frame photos below, note that besides two mounting hooks to hang the equipment, each frame as a keying pin ("Sperrstift"). Each pin is placed at a location that is specific to the equipment to be installed on the frame. That equipment has a hole at the corresponding location. This precludes inadvertent installation of different equipment that would otherwise fit on the frame.

FuG 120 frames

Fig. 92: Rahmen RSV 120 - mounting frame for the SV 120 printer amplifier

(source: Fig. 20 in ref. 200)

FuG 120 frames

Fig. 93: Rahmen SGF 120 - mounting frame for the SG 120 filter unit

(source: Fig. 21 in ref. 200)

FuG 120 frames

Fig. 94: Fußplatte UF 120 - mounting frame for the U 120 power supply

(source: Fig. 22 in ref. 200)

FuG 120 frames

Fig. 95: Verteilerdose VD 120 - junction/distribution box

(source: Fig. 18 and 19 in ref. 200)



FuG 120 TEST EQUIPMENT

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):

  • PS 120, Prüfsender: transmitter to test the complete functionality of the FuBL2 plus FuG120. This implies a full "Bernhard" beacon simulator.
  • PschMG 120, Peilschreibmgerät, for measuring paramters of Hellschreiber printers.
  • TOG 120, Tongenerator: an audio signal generator.
  • PV 120 and PV 64, Prüfvoltmeter: multi-range voltmeters.

The PS 120 "Prüfsender" is a complete "Bernhard" beacon simulator: it outputs 30-33.3 MHz radio frequency signals to the EBL3 radio receiver of the on-board FuBL2 radio-navigation system. Hence, it has an antenna connector on the front of the unit (labeled "Antennenbuchse" at the bottom right in Fig. 96). The unit measures 68x51.5x21.9 cm (WxHxD, ≈26.8x20.3x8.6 inch) and weighs about 40 kg (≈88.5 lbs); p. 347 in ref. 212). The unit was made by Telefunken (ref. 44).

FuG 120 test equipment

Fig. 96: Prüfsender PS 120 - test signal generator

(source: Fig. 3 in ref. 201)

FuG 120 test equipment

Fig. 97: rear view of the Prüfsender PS 120 - test signal generator - main cover and module-covers removed

(source: Fig. 4 and 5 in ref. 202: note the notched disk installation at the top center)


The next figure shows a printout that was generated with a PS 120. The paper tape is a little over 4 cm wide, so it was printed with an HS 120 printer.

azimuth track

Fig. 98: Print-out generated with a PS 120

(source: Fig. 2 in ref. 202; the tape is a little over 4 cm wide as the pages in ref. 202 are DIN A4 size paper)

The Hellschreiber pixel sequence for the compass symbology was generated with a rotating notched disk - a standard implementation for Hellschreiber senders. Note that the azimuth trace in the print-out above is repeated every 10 degrees. This is why the notched disk, which is clearly visible in Fig. 99 below, only has about 36 notches. They correspond to the vertical line segments of the letter R, the numerals 3 and 4, and the tick marks for 1, 5, and 10 degrees. As the "Bernhard" beacon rotated at 2 rpm, the disk rotated at 2 rpm x 360°/10° = 72 rpm. The diameter of the disk is about 15.5 cm (≈6 inch), based on photogrammetric analysis of Fig. 97 above.


FuG 120 test equipment

Fig. 99: Close-up of the notched disk module ("Tastgerät" = keying device) of the PS 120

(source: Fig. 5 and 6 in ref. 201)

The PS 120 also had to simulate the 1800 Hz signal of the twin-lobe beam, with its amplitude change during rotation of the "Bernhard" beacon. This could have been done with an appropriately shaped "propeller" in combination with a photocell. However, no such device is visible in the photos. It is not the 12-blade ventilation fan behind the strobe disk: it would have been turning too fast, there is no light bulb + photocell anywhere near it, and the blade shape would have been wrong. Possibly, the envelope of the signal amplitude was simply generated with a slow sine wave, with a large offset:

PS 120 test equipment

Fig. 100: Possible method that was used in the PS 120 to generate the twin-lobe signal strength envelope

(adapted from Fig. 2 in ref. 202)

The required clipping need not have been done in the PS 120, as this was already done in the SV 120 printer amplifier. The compass scale segment printed in Fig. 98 spans 50° and would be covered by two sine wave cycles. The beacon rotates at 12°/sec. Hence, the envelope-modulating sine wave frequency would have been 12°/sec / 50° ≈ 0.5 Hz.

The designator of the PschMg 120 "Peilschreibmeßgerät" suggests that it was used for measuring certain parameters of Psch 120 / Psch 120a printers. I.e., not for actively testing the printers (by injection of test signals). From the photos immediately below, it is not clear if the unit included any vacuum tubes (valves). The unit does not include any measurement instruments. Possibly it is primarily an interface box that was used in combination with other test equipment.


PschMg 120 test equipment

Fig. 101: Peilschreibermeßgerät PschMg 120 - bearing printer test set

(source: Fig. 7 and 8 in ref. 203)


The TOG 120 tone generator probably produced a selectable 1800 Hz or 2600 Hz sine wave with a manually adjustable amplitude. This would have sufficed to test the SV 120 printer amplifier, the SG 120 dual audio filter unit, and the HS 120 or Psch 120(a) printer. The printer would have printed two solid traces (i.e., without white pixels). The unit was made by Telefunken (ref. 44).

FuG 120 test equipment

Fig. 102: Tongenerator TOG 120 - tone generator

(source: Fig. 1 and 2 in ref. 203)


The test equipment set included two custom "Prüfvoltmeter" test voltmeters: the simple PV 64, and the multi-range PV 120. The latter has a toggle switch for selecting "with/without printer". The PV's were made by Telefunken (ref. 44).

FuG 120 test equipment

Fig. 103: Prüfvoltmeter PV 62 - multi range voltmeter

(source: Fig. 5 and 6 in ref. 203)

FuG 120 test equipment

Fig. 104: Prüfvoltmeter PV 120 - multi range voltmeter

(source: Fig. 3 in ref. 203)


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 (10th 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).

Apparently, a drawing exists that implies installation of a Psch 120 "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. Fig. 105 below shows a piece of equipment above the FuG 16 ZY (VHF telephony/telegraphy transceiver and transponder), between the pilot and the navigator/radio-operator behind him. Based on the size of the equipment, it could indeed be a Psch 120 paper tape printer. A piece of paper tape seems to leave the lower left corner of the equipment. The installation orientation of the equipment also makes sense: the viewing window of the Psch 120 is in its cover, and the printed tape would move right-to-left - as it should, to read the printed symbology.

Messerschmitt Me-262

Fig. 105: The night-fighter version of the Me-262 - with Psch120 ?

(sources: archives of the San Diego Air & Space Museum (SDASM); original photo 1 & 2: no ©, since US Gov't; Psch120: ref. 198A)

Messerschmitt Me-262

Fig. 106: RgK120a and Spkf1a of the FuG120a - to the right of the rear seat in an Me-262 B1


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 never entered 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).

Dornier Do-335

Fig. 107: Dornier Do-335 "Pfeil" with push-pull propeller arrangement


Arado Ar-234B

Fig. 108: Arado Ar-234 "Blitz" - the world's first operational jet-powered bomber


Junkers Ju-388

Fig. 109: Junkers Ju-388J night fighter


Junkers Ju-88

Fig. 110: 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" beacon Be-8 at Schoorl (Bergen) in The Netherlands (ca. 155 km to the northwest) and Be-13 at Buke in Germany (ca. 155 km to the southeast ). It is also ca. 330 km southwest of the "Bernhard" Be-9 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).

Junkers Ju-388

Fig. 111A: 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)

Junkers Ju-388

Fig. 111B: Translated transcript of Fig. 110


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, 217. The airborne part of the FuBl 1 system is the EB.3, a militarized version of the Lorenz EB.2. This system was invented in the early 1930s by Ernst Kramar, Walter Hahnemann, et al (Lorenz Co., e.g., US patent 2,072,267 and 2,217,404) 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 RV 12 P 2000 (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.

Note that the EBl 3 receiver does not contain audio amplifier stages, see Figure 112. The AM envelope-detector of the EBl 3 is an RV 12 P 2000 tube that is used as rectifier diode. Its output is passed straight to the EBl 2 receiver (and, when used with the FuG 120, via the UG 120 switch box to the SV 120 printer-amplifier). The input of the EBl 2 has the DC-blocking capacitors, an isolation transformer, and amplifier/filter stages for a headset output, to generate the normal AGC-signal for the EBl 3, and signals for the AFN2 indicator.


EBL2 EBL3

Fig. 112: Block diagram of the EBL3 and EBL2 receiver

(source: adapted from ref. 72)

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 an optional 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.

EBL 1 receiver

Fig. 113: Receiver model "EBl 1"


EBL 2 receiver

Fig. 114: 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. The EBl 3 measures 23x14.3x15.6 cm (WxHxD, ≈9x5.6x6 inch).

EBL 3 receiver

Fig. 115: Receiver model "EBl 3H1"


EBl 3H turning

Fig. 116: Receiver model "EBl 3H"

(courtesy Erich Werner, used with permission)

EBl 3H  receiver

Fig. 117: Receiver model "EBl 3H"

(source: Figure 5.2 in ref. 78)

EBL 3 receiver

Fig. 118: "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) in 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).

AS503-OS receiver

Fig. 119: 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 standard 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):

  • The printer Psch120"k" of the FuG 120k, and its manufacturer.
  • Involvement in the development of the Psch120/FuG120a by the Lorenz company in Falkenstein/Thuringia.
  • Was the original April/May 1941 RLM order for 2000 HS 120 printers maintained, or modified to a smaller quantity when 2400 Psch120 were ordered in August 1941?
  • Confusion Psch 120 vs. Psch 120a.
  • Functionality/purpose of the PschMg 120.
  • On-board aircraft system Flugzeugbordanlage "Ulrich" (including modified "Bernhardine" printer and tone-filter), which was to be an improvement for the "Knickebein" beam system.
  • Hellschreiber of the FuG 139 "Barbarossa" and of the FuG 126k "Baldur K / Bord".
  • Hellschreiber of the Lorenz "Sägezahn" command upload system.
  • The color of HB 50 printer ink.

If you have any additional information, please contact me!


PATENTS

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

Patent number Patent office Year Inventor(s) Patent owner(s) Title (original) Title (translated)
767354 RP 1936 - Telefunken G. für drahtlose Telegraphie m.b.H. Verfahren zur Richtungsbestimmung Method for direction-finding [this is the primary "Bernhard" patent]
730625 RP 1937 R. Hell Dr.-Ing. Rudolf Hell Verfahren zur Registrierung des Verlaufes veränderlicher Stromkurven Method for printing the trace of varying signals [pulse-width modulator, 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 [proposes 3rd beam, for AGC]
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 [print medium is erasable Printator foil disk instead of Printator tape]
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 - Marconi's Wireless Telegraph Co. Ltd. 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

REFERENCES


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

External links last checked: October 2015


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©2004-2017 F. Dörenberg, unless stated otherwise. All rights reserved worldwide. No part of this publication may be used without permission from the author.