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

Latest page update: 31 January 2017

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Siemens-Hell-Schreiber 80, or simply "Hell-80", is the latest & last model Hellschreiber that was developed and produced by the Siemens-Halske company. Development of the Hell-80 started in 1958. It is the world's first fully electronic teleprinter: only the keyboard, punch-tape reader, and the Hell-printer have moving parts. Ref. 1-10.

The Hell-80 can be operated in two modes:

  • Synchronous - like the 1930s-1940s Presse-Hell and the 1935-45 Feld-Hell. Note: "synchronous" does not mean "synchronized".
  • Asynchronous - this is start-stop operation, with a start-pulse sent as part of each transmitted character, like Hell-72/73, 39, 40, and 44.

Both modes are selectable when operating from the built-in punch tape reader. For keyboard operation, only the start-stop mode is available. As Hell-80 can operate in synchronous mode, its printer has a two-start spindle, prints two identical lines, and uses 15 mm wide paper tape.

The Hell-80 operates at exactly twice the speed of the traditional Feld-Hell. So, if you print Hell-80 signals with a Feld-Hell machine (or software), you will see four lines of text instead of two!


Hell-80 signals printed with Feld-Hell - tuned to the "mark" tone

As Hell-80 is FSK, you can actually select between printing white-on-black and black-on-white ("reverse video"), by tuning to the "black" tone or to the "white" tone (300 Hz shift).


Hell-80 signals printed with Feld-Hell - tuned to the "space" tone

Hellschreiber-capable software is available for sending & printing synchronous Hell-80 signals, and for sending asynchronous (start-stop) Hell-80 signals, but not (yet) for printing the latter.


The initial model ("T. typ. 80a", "Hell-80a") was intended for both the West-German military (the Bundeswehr) and commercial customers. Its development started in 1958, and a first batch of 15 units was produced early 1961 (ref. 1). This model was only suitable for use over teletype/teleprinter lines - not for use over phone lines and via radio.



(source: ref. 1)

MODEL "T TYP 80" / HELL-80

The Siemens Streifen-Fernschreiber Satz (tape-teleprinter set) model T. typ. 80 was developed exclusively for the Bundeswehr (Bw, the armed forces of what was West-Germany at the time). After a three-year development period, production started in 1965 at Siemens in Munich. Some 225 units entered service between 1965 and 1975 (ref. 11). The system was used by the Bundeswehr until around 1985, when it was decommissioned due to lack of compatibility within NATO. As the Hell-80 was designed for military field operations, it is also referred to as a "Feldfernschreiber" (field-teleprinter), just like the 1935-45 Siemens Feld-Hell.

Contrary to the initial model T. typ. 80a, the T. typ. 80 was could be used for communication over phone lines and via radio, but not over teletype/teleprinter lines.


Equipment label on my Hell-80 machine from 1970


Front-view of my Hell-80

Here is a summary of the characteristics of the Hell-80 (ref. 12):

  • Technology:
  • Fully transistorized / solid-state (a "world's first"); modular design
  • Magnetic core memory for the character font.
  • Modulation: two-tone FSK with 300 Hz shift
  • 1625 Hz (white pixel / no pixel, "space" tone). When no characters are transmitted for a certain amount of time, the amplitude of the 1625 Hz tone is reduced.
  • 1925 Hz (black pixels, "mark" tone)
  • Equivalent FM modulation: center frequency of 1775 Hz and a deviation of 150 Hz.
  • Signaling: 1260 Hz, for remote control of (or by) the machine at the opposite Hell-80 station.
  • Keyboard: same character set as Siemens-Hell 72/73 ("GL"/"AG"), with additional possible characters Ñ Á Ä Ö
  • Modes:
  • Asynchronous (start-stop; uses start-pulse in first column of character matrix, like Hell-72/73); from built-in punch-tape reader or from keyboard.
  • Synchronous (no start-pulse, like Feld-Hell): only from the punch-tape reader. It is technically possible to use this mode from the keyboard, but few operators achieve sustained 5 cps typing speed. As the paper tape moves fast and continuously, this causes large spaces to appear between printed characters, which is impractical.
  • Font raster: 7x9 (vs. 7x14 for Feld-Hell and Hell 72/73)
  • Data rate: 315 baud (3.175 msec minimum pulse width)
  • Transmission rate: 5 characters per sec (2x Feld-Hell)
  • Telegraphy speed: 50 WPM
  • Channel bandwidth: 2000 Hz recommended (1100 Hz minimum); "necessary bandwidth" per ITU: 945Hz. However, the "Schrittfrequenz" ("Bildpunkfrequenz" = pixel rate = 1 / time required for "1 white pixel + 1 black pixel") is 157.5 Hz. This implies a necessary bandwidth of 3 x 157.5 = 475 Hz.
  • Duty cycle: 100 % (in both asynchronous and in start-stop mode)
  • Phone line interface: 2- and 4-wire
  • Allowed signal path attenuation: 35 dB / 4 neper (same as Siemens-Hell 72/73/39/40/44)
  • Punch-tape reader: built-in. Uses International Telegraphy Alphabet No. 2 (ITA2) standard (5-bit, superseding the 1901 Murray-code and 1874 Baudot-code). Uses standard 11/16 inch punch-tape.
  • Remote control: remote (de-)activation via the 1260 Hz signaling tone. Automatically reverts to standby mode if no signals are received for more than 40 sec.
  • The receiving machine can also remote control the sending station, e.g., to stop transmission from punch tape while in start-stop mode. However remote control in this direction requires full duplex operation (4-wire), and is not available during normal communication via radio (unless full duplex via split-frequency operation).
  • Power:
  • 24 volt DC nominal; 21-30 volt DC max. 1.6 amp nominal; or
  • 110/127/220/240 volt AC (±10%), 40-60 Hz.
  • Reduced dissipation when in standby mode
  • Weight: 30 kg (≈ 66 lbs)
  • Dimensions: 47x51x29 cm (WxDxH) (≈ 18½ x 20 x 11½ in)
  • Carrying case: aluminium. The case is waterproof (not just watertight!). Note: the Hell-80 unit remains in the case, only the front cover is removed.


The Hell-80 - opened, showing its modular design

(cover of the box with the circuit cards removed)


Looking down into the opened Hell-80

(cover of circuit cards removed; click here for full-size image)

3D/stereoscopic photos of my Hell-80 machine are on this page.

The easiest way to hook up a Hell-80 machine to a transceiver, or to the soundcard of a PC, is to select "4 Draht-Betrieb" (4-wire operation) on the machine's interconnect panel. This configures the interface as a 2-wire audio input, plus a separate 2-wire audio output. The interfaces are transformer-coupled, so no issues with DC offsets. I checked the input and output with my scope, just to be safe. No signal on the input, and 1.8 Vpp on the output ("Sendepegel" (output level) selected to -1 Neper, next to the 2 vs. 4 wire selector button). Obviously this output level needs to be reduced via a simple voltage divider (e.g., a potmeter), before connecting it to the microphone input of a transceiver or PC soundcard (though it is OK for the line-input of a soundcard).


Signal and power interfaces of the Hell-80

A transceiver can also be hooked up via the round receptacle marked "Funkgerät" - transceiver. It has 10 spring-loaded contacts, and is located at the top left of the front panel. This is a type U-79/U chassis-mount receptacle. It mates with the standard NATO (MIL-C-10544) audio connectors U-77/U and U-127/U (90º angled connector). U-78/U is the connector equivalent of the U-79/U receptacle. Surplus U-77/U connectors are still readily available (e.g., here). This connector provides access to the 4-wire interface, plus PTT. There are two PTT pins. They are floating (interconnected via two relay contacts in series), so they can be used with any type of PTT input (pull up, pull down,..). Note that the PTT is not accessible via any of the other connectors.


Hell-80 has a standard NATO audio connector type U-79/U


Inside of the cover - spare paper rolls and a compartment for spares/accessories


The list of spares/accessories

(110/220 Vac power cable, 24 Vdc power cable, transceiver patch cable, soft cotton cloth, dust brush (goat hair!), ink roller set, fuses, rolls of paper tape)


Accessories of the Hell-80

A small weak point in the design is the choice of the timing belt (a.k.a toothed, notch, cog, timing, or synchronous belt; D: Zahnriemen, F: courroie dentée) between the speed control knob on the front panel, and the speed regulator in the motor module at the back of the machine:


Location of the timing belt inside the machine, and the broken joint of my original belt

The original belts have a joint that is glued, instead of fused. Sooner or later, such glued joints become undone, as the glue creeps and dries out, and the belt is flexed. There is no spare belt... The belt has a standard T-profile, a pitch of 5 mm, has 100 "teeth" (hence, 500 mm overall length), and a width of 6 mm. So it is a regular "T5 500 6" belt, and modern replacements either have a fused joint or no joint. I have replaced my broken belt with an Optibelt ALPHA "T5 500 6".

Arie van Ooijen (PE1AQB) has constructed several Hell-80 compatible printers (start-stop). I have posted pictures and info on the Homebuilt Hell-printers page. He also modified his Hell-80 machine to be compatible with Feld-Hell (ref. 13).



Print-out of the Hell-80 character set on my machine

The Hell-80 uses a font raster that is slightly different from the one used by the Feld-Hell and the Hell-72 "GL"/ 73 "AGL". The Hell-80 raster is 7x9, rather than 7x14. During start-stop operation, a start-pulse is transmitted in the first column - as for the Hell-72/73. The binary form of the Hell-80 font is here.


The 7x9 font of the Hell-80

(the 5-pixel start-pulse in the first column is only transmitted during start-stop mode)

The "Video and Sounds" section below has a number of audio recordings of Hell-80 signals (incl. actual shortwave communications).

Like the Feld-Hell and Hell-72, the Hell-80 font is stored in non-volatile memory: without power, the memory contents is retained indefinitely. However, the Hell-80 memory is not a mechanical character-drum, but consists of magnetic core memory. This technology dates back to the early 1950s. It uses 35 pairs of small ceramic magnetic rings (the "cores", D: "Ringkerne"). Several wires are treaded through each of the cores, to provide read/write access. Addressing signals are provided by the decoder-card shown further below.


Magnetic cores, used in the Hell-80 character generator memory

(source: Fig. 2 in Rudolf Hell's German patent 1086738 and US patent 3255313)


The pixel-memory card ("Bildpunktregisterkarte") of the Hell-80

(also shown in 3D on my "3D stereoscopic photos" page)

The above pixel-memory card has 80 magnetic cores, 56 glass-encapsulated germanium diodes of type OA5 (Siemens; the datasheet is here), and 3 germanium PNP transistors of type Siemens ASY11-1 in a TO-1 package.

The photos below show the address-decoder card that is associated with the above pixel-memory card. It generates a pulse sequence, based on the selected key of the keyboard or the 5-bit code received from the punch tape reader. It contains 16 magnetic cores, and as many switching transistors. The latter are of type OC123, made by Valvo Radioröhrenfabrik GmbH (Philips) in Hamburg. Mullard (UK) also made this type. The OC123 is a bipolar germanium PNP junction transistor, with a max power dissipation of 300 mW, max Ic of 500 mA, a typical static gain hFE of 160, max Uce of 50 V, f(T) of 1.5 MHz, and a TO-7 metal-case package (h=9 mm, Ø = 8 mm, ≈ 0.3x0.3 inch). Official equivalents are the ACY24, ASY48, ASY77, and BFX87. The AC128 has been used successfully as replacement.


The decoder card ("Decodierer") of the Hell-80 - 16 ceramic magnetic rings


Close-up of the decoder card


The documentation of the Hell-80 does not reveal parameters of the start-pulse detection, nor when (and for how long) the printer is enabled upon detection of a start pulse. Some time after detection of the start-pulse, the shaft of the printer spindle is engaged via an electro-magnetic clutch mechanism, and the printer is enabled via a notch and associated contacts. After 6 revolutions, this shaft is halted. Clearly, the speed of the printer shaft depends on the speed of the local motor. However, the speed at which pixels are transmitted, is entirely independent of the motor speed! Instead, it is driven by a very accurate and stable crystal-clock time-base. This means that the slant of the printed text can be adjusted locally, without receiving text from an other machine!

In 2011, Arie van Ooijen ( PE1AQB) and I ran a number of tests, to characterize the timing of the start-pulse detection and printer of the Hell-80 machines. From his other Hell-80 experiments, Arie had a programmable Hell-80 character generator and an FSK tone generator. We defined several dozen very specific test characters, and Arie programmed the character generator and made audio files (zipped and downloadable here; 15 MB). He also added a 360º protractor disk to the shaft of the printer spindle, to be able to accurately measure shaft rotation versus opening & closing of notch-driven contacts:


The aim was to determine four parameters:

  • Time to detect the start-pulse
  • Time between detection of the start-pulse, and enabling of the printer
  • Time during which the printer remains enabled
  • Time between detection of the start-pulse and re-enabling the detection for the (next) start-pulse.

Obviously, the start-stop mechanism must still work, even when sending and the receiving machines have motor speeds that are at the maximum allowed difference. The nominal start-pulse has a duration of 5 pixels, that is: 15.87 msec. The start-pulse detection must trigger significantly faster than that. Our tests determined that the detection-time is only 4.4 - 4.8 msec. That is, about 1.5 out of the 5 start-pulse pixels! The detection is done by analog circuitry (an other electronic Hell detection method is described in ref. 14). The measured variation in the detection time is equivalent to a mere 1/8 of the nominal pixel duration. It is partly driven by the cycle time of the 1625 Hz pixel-tone frequency (0.6 msec) and the fact that pulse transmission does not start at a zero-crossing of the sine-wave of the tone. The pulse detection is disabled upon that detection, and remains disabled for 53.5 pixels. This effectively means that detection of the next start-pulse is enabled just before the printer is disabled. The printer is enabled 3.5 pixels after start-pulse detection, and remains enabled for about 52 pixels. That is, the printer is enabled 3 pixels before the first font-pixel is expected (i.e., the 2nd pixel from the bottom of the 2nd column), and remains enabled for 6 pixels after the last "official" pixel (i.e., 1 pixel before the top of the 6th column). The timing diagram below captures the conclusions of our tests:


Experimentally derived timing diagram of the Hell-80 start-pulse detection and printer timing


Timing diagram - transposed to the nominal Hell-80 font matrix


Printer of a Hell-80 machine in action

Below are several sound clips of actual Hell-80 transmissions. They are suitable for testing Hell-software and Hell-80 machines. These and other sounds from Hell (machines) are on this page.

Hell-80 QSO (multi-station)

Both start-stop and synchronous transmissions, recorded on 1-Mar-2010 around 7050 kHz.

Hell-80: synchronous mode

(basically double-speed Feld-Hell mode, not start-stop).

Hell-80: QSO in start-stop mode (Part 1)

Recorded on 24-Jan-2011. Click here for a scan of the associated paper tape print-out.

Hell-80: QSO in start-stop mode (Part 2)

Recorded on 24-Jan-2011.


Beginning of the first audio file above - printed with my Hell-80 machine in Start-Stop mode


The same audio file - now printed with Multipsk software in synchronous mode

(in synchronous mode, start-pulses are not used as such - they are simply printed just like all other pixels; the paper tape moves continuously)


Patent number Patent office Year Inventor(s) Patent owner(s) Title (original) Title (translated)
1086738 DPA 1958 Rudolf Hell Rudolf Hell Co. Verfahren und elektronischer Vorrichting zur Aussendung von Schriftzeichen im Hell-Code oder einem ähnlichen Code für Blattschreiberempfang (Faksimileverfahren) Method and electronic device for transmittal of characters in Hell-code or similar code, for sheet-printers (facsimile method)
3255313 US 1959 Rudolf Hell Rudolf Hell KG Electronic method of and apparatus for transmitting characters for facsimile sheet printing reception -

Patent office abbreviations:

  • BD = Bundesrepublik Deutschland, Deutsches Patentamt [German Federal Patent Office]
  • US = United States Patent Office

Patent source: DEPATISnet, the on-line public database of the Deutsches Patent- und Markenamt (DPMA, German Patent and Trademark Office).


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