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Single-tone analogue telegraphy

The Hellschreiber was a telegraphy device for transmitting and receiving text-based messages via telephone lines or radio, invented in 1929 by Rudolf Hell in Kiel (Germany). The system works by scanning each character line-by-line from a pre-defined shape, and transmitting it as an on/off audio signal (tone). The system is also known as Typenbildfernschreiber (typeface teleprinter).
At the receiving end, the image is reconstructed by pushing a paper strip against an inked helix spindle in the rhythm of the on/off signal. As it is basically a non-synchronized system, the rotation speed of the receiver's helix spindle has to match the scanning speed of the transmitter.

If the speed does not match, the line of text will be sloped and appears to be 'running off the paper'. The spindle therefore has a double helix, which causes each character to be printed twice. This guarantees that the text remains readable, even if the receiver's speed is somewhat off.

The main advantage of this system is that the text can be transmitted over noisy narrow band radio channels without loosing its readability. Radio noise and interference from other signals, will be visible as random dots in the character image, but generally speaking, the human brain will be able to determine the actual text. This makes the Hellschreiber far more fault-tolerant than a 5-bit digital telegraphy system (telex).
Fellhelschreiber in operational position

Although strickly speaking the Hellschreiber is neither a teleprinter nor a facsimile device (fax), we have listed it under telex as it is used for the transmission of text-based messages. Like a teleprinter, it is a telegraphy system that is used for sending telegrams, but rather than using the digital representation of a character, it scans the character shape from a cylinder, much like a fax machine does. Is some ways, the Hellschreiber can be seen as a forerunner of the 1956 fax. 1

The most commonly known HELL company logo

Below, some aspects of the Hellschreiber are highlighted. For further information, please visit the website of Frank Dörenberg [1], which is a far more complete repository of information and backgrounds on the Hellschreiber, and contains many examples, photographs and further links. Not many people know that Hell also made cipher machines. Click here to learn more about this.

 More about Rudolf Hell
  1. The fax or facsimile was also invented by Rudolf Hell (1956).

The basic operating principle of the Hell transmission system is very simple. When typing on the keyboard, the image of the character that is entered, is scanned from a rotating cylinder. This image is then sent by means of a simple ON/OFF signal, where ON indicates the presence of a dot or pixel. The ON signal can be sent over telephone lines or via radio channels as an audio tone.

At the receiving end, the audio tone is used to drive a solenoid that presses a moving strip of paper against a rotating inked helix. By transferring the ink from the rotating helix to the paper, the image is rebuilt. In principle, this is a non-synchronized system, which means that the motor speed of the receiver has to match that of the transmitter. There are also synchronous variants.
  • Presse Hell
    First version of the Hellschreiber, also known as F-HELL. Uses a 14 x 7 pixel font 1 that is transmitted at 245 baud (5 cps). Initially current keyed, but later converted to 1000 Hz tone-keyed operation.

  • Feld-Hell
    Army variant of the Hellschreiber, made by Siemens & Halske for the German Army. Uses the same 14 x 7 pixel font 1 as Presse Hell, but transmitted at the half the speed: 122.5 baud (2.5 cps). The information is tone-keyed at 900 Hz.

  • GL-Hell
    Asynchronous version of the Hell system that uses a start bit before each 14 x 7 pixel character. Transmits at 300 baud (6.1 cps), using a single tone (1000 or 3000 Hz depending on the model).

  • Hell-80
    The last version of the Hellschreibers used asynchronous Frequency Shift Keying (FSK) with 1625 Hz (white) and 1925 Hz (black) tones, plus an additional tone (1260 Hz) for line signalling. It uses a different 9 x 7 pixel font and transmitted at 315 baud (5 cps).

  • ATF-Hell
    Post-war East-German asynchronous variant with start/stop signalling and a transmission speed of 225 baud (4 cps). Like with the Feldhellschreiber, the information is single tone-keyed at 900 Hz. Each character is defined in a 7 x 7 pixel grid.

  1. Non-synchronized HELL used a font with a raster of 14 x 7, but as each character is printed twice (i.e the spindle has a double helix) the raster is effectively 7 x 7, or 49 pixels.

Presse Hellschreiber
The initial version of the Hellschreiber was used by press agencies world-wide for sending news items around the world via telephone lines as well as via radio (HF and VLF frequencies). It is therefore also known as Press Hell or Presse Hellschreiber. It was introduced immediately after its invention in 1929 and was used well into the 1990s, when it was replaced by digital technology.

Presse-Hell is a quasi-synchronized system that transmits characters, defined in a 14 x 7 pixel raster, at 245 baud or 5 characters per second (cps). The intial version was current keyed and was suitable for use over land lines only. The system was later changed to tone-keying, using 1000 Hz to indicate the presence of a dot. Presse Hell devices were made by many manufacturers.
The Feldhellschreiber is arguably the most well-known and widely spread variant of the Hell­schreiber. The format was first introduced on the Siemens & Halske A2 Feldfernschreiber (field teleprinter), of which more than 30,000 units were built for the German Army. Feld-Hell uses the same 14 x 7 pixel character set as the Presse Hell, but transmits them at half the speed: 122.5 baud or 2.5 cps. Like Press-Hell it is single-tone keyed, but uses 900 Hz instead of 1000 Hz.

Feldhellschreibers were usually grey, but the image on the right shows a rather rare green variant that was made in 1936 especially for the Czech Army. It was restored in 2013 and is now fully operational again.

 More information
Fellhelschreiber in operational position

ATF Hell
Following WWII and the separation of East-Germany from West-Germany, the DDR developed its own variant of the Hellschreiber in 1954/55, using knowledge and parts that were left behind in East-Germany. As it was strickly forbidden in the DDR to use Wehrmacht nomenclature, the machine was designated ATF; the abbreviation of Abtastferschreiber (scanning teleprinter).
The ATF was an asynchronous system, similar to GL-Hell, and was based on the Siemens T typ 58 Feldfernschreiber that was used by the German Army during WWII (Wehrmacht). It used single-tone (900 Hz) ON/OFF communication with start/stop signals at 225 baud (4 cps).

ATF was intially developed for the Kasernierte Volkspolizei (KVP) and entered service in 1954. In 1956 it was also introduced at the Nationale Volksarmee (NVA), the National People's Army of the DDR. All ATF systems were phased out in the late 1950s probably for reasons of compatibility.

 More information
Click for more information about the ATF Schreiber

Although the HELL-principle was patented by Rudolf Hell, and the HELL company produced its own telegraph systems, the principle was used by a wide variety of other manufacturers. The following manufacturers are known to have used the HELL-principle [1]:
  • EMA (Meilen, Switzerland)
  • FIAT - Fabbrica Italiana Apparati per Teledomunicazioni (not the car manufactuer)
  • GPO - General Post Office (UK)
  • Hell
  • LMT - Le Matériel Téléphonique
  • PTW - Post- und Telegraphen Werkstätte (Salsburg, Austria)
  • RCA
  • RFT (ATF Schreiber)
  • Siemens & Halske
  • Teletype (Model 17)
  • Thomson
  • Toho Denki KK
  • TTK/Sony
  • US Signals Corps (RC-58-B, BC-908/BC-918-B)
  • Creed
  • Gretag (ETK 14-bit teleprinter)
  1. Frank Dörenberg, Hellschreiber website
    Retreived June 2013.

Further information

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© Crypto Museum. Created: Wednesday 29 June 2016. Last changed: Saturday, 09 July 2016 - 10:40 CET.
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