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Single-tone analogue telegraphy

The Feldhellschreiber (Field Hell Writer), or Feld-Hell (Field Hell), was an analogue telegraphy system for transmitting and receiving text-based messages via standard telephone lines or short wave (SW) radio channels. It is the Army variant of the Hellschreiber (Hell Writer), invented in 1929 by Rudolf Hell in Kiel (Germany), and was used heavily by the German Army during WWII. It is also known as Feldfernschreiber, as Siemens-Halske-Feldschreiber, and as S-H-Feldschreiber. The Siemens designator was T.typ.58 and within the Wehrmacht it was known as T Bs/24a-32. 1

The Feld-Hell format was first used 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 painted grey and came in various shades, depending on the army department (e.g. Luftwaffe) or the year in which they were built. The image on the right shows a typical Feldhellschreiber in a rather uncommon green colour, that was built for the Czech Army in 1936. The machine is part of our collection and was fully restored in 2013 by Arthur Bauer.

The machine is housed in a panzerholz transport case and consists of a keyboard, scanning drum, printer, motor and an amplifier. The amplifier is fixed in the top right corner, but the keyboard can be pulled forward for easier operation.
Fellhelschreiber in operational position

The system works by scanning each character line-by-line from a pre-defined character shape on a drum, and transmitting it as a single (on/off) audio tone of 900 Hz. When transmitted over a noisy narrow-band short wave (SW) radio channel, a Feldhellschreiber signal sounds like this:

The receiver then reconstructs the image 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.

  1. TBs = Typenbildschreiber (typeface printer), yet another name for the hellschreiber.

Closed case
Feldhellschreiber with front cover removed
Keyboard in operational position
Close-up of the helix spindle
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Closed case
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Feldhellschreiber with front cover removed
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Keyboard in operational position
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Close-up of the helix spindle
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The diagram below gives an overview of the controls and features of the Feld-Hell machine. At the rop right is the amplifier. Although it can be removed easily, it is the only fixed part of the machine. When receiving, it converts the line signal into an on/off signal that controls a solenoid below a moving paper strip, in such a way that characters are printed on the paper strip.

When transmitting, the selected character is scanned line-by-line from a rotating drum on which each character is represented by a series of pixels. These pixels can be seen as a series of ON/OFF signals that are then converted by the amplifier into a series of 900 Hz tones.

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The electromechanical subsystem is mounted on a rail, so that it can be pulled forward for easier operation. This is done by pushing the keyboard release lever to the left and then pulling the keyboard outwards. This also brings the motor and the printer forward. The text is printed onto a paper strip that is fed in from a storage compartment below the keyboard, routed in between an ink roller and a rotating helix spindle, leaving the machine at the left. A solenoid, or electro­magnet, pushes the paper strip against the helix spindle in the rhythm of the 900 Hz audio tone.

Feldhell in use
The photograph below was taken just before or during WWII and comes from a soldier's private photo album. It shows two German soldiers working in a message centre. At the center is a Feldhellschreiber, which is operated by the man on the left. The Hellschreiber is most likely used via land lines here, as it appears to be connected to the Army field phone to its right.

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Another phone is placed on top of the Hellschreiber. At the far left, behind the leftmost operator, is another Feldhelschreiber, which is partly obscured by a third field phone. The leftmost operator is reading a message from the Hellschreiber's paper strip, and writing it down on a message pad.

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Here is another image of a Feldhellschreiber in use during WWII. The picture was probably taken in a barn as we can see all kinds of attributes around the group of five soldiers at the centre. The soldier standing at the right is operating a German field phone, whilst the one sitting on a chair is typing a message on the keyboard of the Hellschreiber. The lid of the Feldhellschreiber is placed against the wall on the right. Click the image for an enlargement of the centre part [3].

Rediscovered by HAMs
After WWII, the Feldhellschreiber was no longer used and the machines landed in storage or, worse, on the scrapheap. Althoug press agencies world-wide continued to use the so-called Presse-Hell system, its use and its operating principle were largely forgotten by the mass.

All that changed when, in the mid-1970s, several radio amateurs (HAMs) rediscovered it more or less simultaneously. After some experiments and obtaining the necessary permissions from the authorities, HELL appeared to be excellent for communication via the short wave band, and a new amateur communications mode was subsequently born. In the Netherlands, Hans Evers (PA0CX) wrote an interesting article about the rediscovery of the Hellschreiber [4] in Electron, the Dutch HAM radio magazine. It was later translated and published in Ham Radio [5]. It was soon followed by articles from all over the world, including an interesting one by Helmut Liebich in Germany [6].

Ever since the rediscovery, HELL has been a popular mode on the short wave bands and is still being used today. As original Hellschreibers are a rarity these days, people have found alternative ways of creating HELL, by means of a variety of home-made projects as well as with a modern computer. There is a group of enthusiasts that have set up the so-called Feld-Hell Club to promote the use of HELL [7]. For those that are interested, there is another group that organizes an annual HELL Meeting in The Netherlands as well. See Frank Dörenberg's website for details [1].

Power socket
The Feldhellschreiber should be powered by a 12V DC source, such as the battery of a car, or a mains power supply unit (PSU). The power source should be connected to the wide two-pin socket at the top right of the amplifier. The (+) terminal is 5 mm thick, whilst the (-) terminal is 4 mm thick. This is done to prevent the power plug from being inserted the wrong way around.

  1. 12V (+)
  2. 0V (-)
Peripheral socket
Some (but not all) Feldhellschreibers have a circular 12-pin socket for connection of peripheral equipment. When present, this socket is located at the bottom right of the amplifier. In some cases it is covered by a metal swivel plate. The pin-out of this socket is given below. Please refer to the circuit diagram [A] for a full description of the pins of this socket.

  1. Line (A), Input (A)
  2. Input (B)
  3. Center contact of socket
  4. Line (B)
  5. 12V (+) when switched on
  6. 12V (+) when switched on
  7. 0V (- terminal of battery)
  8. Output
  9. ? +12V, -165V return
  10. HT voltage
  11. 12V (+) in standby
  12. LT voltage
Detailed description
An extremely detailed description of the Feldhellschreiber and its operations, complete with many examples and animations, is provided by Frank Dörenberg in France. If you want to know exactly how the Hellschreiber works and what other variants are available, you MUST visit this site [1].

 Visit Frank Dörenberg's Feldhell page (off-site)

  1. Oberkommando des Heeres, Der Feldfernschreiber
    Original Wehrmacht Feldhellschreiber operator's manual (German).
    D 758/1. Berlin, 1 April 1941. 1
     Annotated English translation (off-site)

  2. Luftnachrichtentruppe, Der Feldfernschreiber
    Original Luftwaffe training manual (German).
    L.Dv. 702/1 Heft 213. Berlin, 21 November 1940. 1

  3. Feldhelschreiber, Betriebsanweisung
    Single sheet, to be placed in frame of case lid.
  1. Document obtained from [1].

  1. Frank Dörenberg, Hellschreiber website
    Retreived June 2013.

  2. Unknown protographer, Photo of two German soldiers using a Feldhellschreiber
    Genuine (pre) 1945 photograph. Date unknown. #CM301749. Digitally enhanced.

  3. Unknown protographer, Photo of 5 German soldiers around a Feldhellschreiber
    Genuine WWII photograph. Date unknown. #CM300530. Digitally enhanced.

  4. Hans Evers (PA0CX, DJ0SA), Hellschreiber - een herontdekking
    Electron, June 1977 (Dutch).

  5. Hans Evers (PA0CX, DJ0SA), The Hellschreiber, a rediscovery
    Ham Radio, December 1979 (English).

  6. Helmut Liebich (DL1OY), Nostalgie oder Realität?
    Funkschau, November 1990 (German).

  7. Feld Hell Club (website)
    Founded in 2006. Retrieved June 2013.
Further information
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Crypto Museum. Created: Saturday 09 July 2016. Last changed: Thursday, 16 April 2020 - 10:27 CET.
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