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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
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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.
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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:
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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.
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TBs = Typenbildschreiber (typeface printer), yet another name
for the hellschreiber.
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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.
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.
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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.
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.
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].
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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].
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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.
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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.
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- Line (A), Input (A)
- Input (B)
- Center contact of socket
- Line (B)
- 12V (+) when switched on
- 12V (+) when switched on
- 0V (- terminal of battery)
- Output
- ? +12V, -165V return
- HT voltage
- 12V (+) in standby
- LT voltage
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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)
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Document obtained from [1].
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- Frank Dörenberg, Hellschreiber website
Retreived June 2013.
- Unknown protographer, Photo of two German soldiers using a Feldhellschreiber
Genuine (pre) 1945 photograph. Date unknown. #CM301749. Digitally enhanced.
- Unknown protographer, Photo of 5 German soldiers around a Feldhellschreiber
Genuine WWII photograph. Date unknown. #CM300530. Digitally enhanced.
- Hans Evers (PA0CX, DJ0SA), Hellschreiber - een herontdekking
Electron, June 1977 (Dutch).
- Hans Evers (PA0CX, DJ0SA), The Hellschreiber, a rediscovery
Ham Radio, December 1979 (English).
- Helmut Liebich (DL1OY), Nostalgie oder Realität?
Funkschau, November 1990 (German).
- Feld Hell Club (website)
Founded in 2006. Retrieved June 2013.
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© Crypto Museum. Created: Saturday 09 July 2016. Last changed: Thursday, 16 April 2020 - 09:27 CET.
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