The Equipment

Early Developments In 1929 Hell demonstrated an electrochemical character scanning device for transmitting the text. This used fingers to measure the characters on moistened paper, but for that reason was not practical. In 1931 the helical worm and hammer electromechanical scanning device first appeared. Another early system used an electrochemical printing system. In 1935 Hell supplied portable Hellschreiber machines in "kit bags" to the German Army (the Wehrmacht). By 1940 when the landmark paper Die Entwicklung des Hell-Schreibers (The Development of the Hell-Printer) was published, all the important technology had already been developed. (Picture of experimental electrochemical device from Die Entwicklung des Hell-Schreibers, 1940 by R. Hell)
F-Hell The F-Hell machine was a synchronous machine which operated at 5 characters/sec (245 baud), and used ITA2 code punched tape as a transmitter source. This machine was intended for press service and was widely used before, during, and after WWII. The F-Hell machine was receive only, as the transmissions were from paper tape. The F-Hell equipment was introduced in 1932, and incorporated the double line printing technique. Nothing is yet known about the companion transmitter, although the system was known to be still transmitting sports news on 44.25 kHz as late as the mid 1980s. (Picture courtesy of Arie PE1AQB)
Feld-Hell The now well known portable military machine, the Feldfernschreiber or "Field Text Writer" dates from 1932. It is a four-valve, motor driven, 12V DC operated unit with a drum based transmitter and a worm and hammer receiver system. The Feldschreiber operates at 2.5 characters/sec, probably because of the limitations of the keyboard mechanism. The machine was designed for field-telephone land-line and radio use. The keyboard is very limited - only upper case letters, numbers and the symbols + - ? /, and a special technique is required to press the keys to maintain correct typing speed without gaps. The Feldschreiber uses double row printing and a specially designed 14 x 7 font with minimum possible bandwidth. The on-off keyed tone is 900 Hz. The techniques, protocol and font used by this machine are still in use today. (Picture courtesy of Ko Versteeg NL9222)
GL-Hell The GL-Hell machine (Siemens model 72C) is a post-war asynchronous machine (1950) intended for land-line press service. It operates at 6.1 characters/sec (300 baud), and includes a paper tape reader. It transmits a single tone, 1000 or 3000 Hz, on - off keyed. The purpose of the 3000 Hz tone was to allow the GL-Hell and a voice telephone to share the same circuit. The transmitted signal has a start pulse up the left edge of each character, and although text no longer slopes if the speed is in error, individual characters can slope. The GL-Hell featured automatic call answering, signalling and clearing, so could be used on a common public telephone line. The system is not suitable for use on HF due to serious garbling of text caused by received noise. The machine prints a single row of text, and the keyboard is normal typewriter style. (Picture courtesy of Arie PE1AQB)
L-Hell The L-Hell machine (Siemens model L) dates from about 1950, and is an asynchronous receive-only unit for land-line press service. The L-Hell is believed to operate at 6.1 characters/sec (300 baud). The machine prints a single row of text. More information required. (Picture courtesy of Arie PE1AQB)
Hell-80 The Hell-80 machine is a portable transistorised machine for military service, introduced about 1960. It will operate from -20 to +50°C in both synchronous and asynchronous modes, at 5 characters/sec (315 baud), and includes a CCITT No. 2 code paper tape reader and NATO standard line interface. This machine uses a different (9 x 7) font to all the others, and was the first Hell machine to use FSK. It uses 1625 Hz white, 1925 Hz black, and 1260 Hz signal tones, and the receiver uses an AM technique. In asynchronous mode, this machine is ideal for unattended operation. (Picture courtesy of Arie PE1AQB)
LMT The French company Le Matériel Téléphonique developed a concurrent tone system using seven wide spaced tones. Using a largely mechanical technique, this equipment used seven tone generators and generated characters as horizontal vectors. The receiving equipment used seven separate matched filters and amplifiers, each with independent AGC, driving seven stylii to write on carbon strip paper. The input to the transmitter was from punched tape or buffered parallel keyboard, both using the ITA2 code. The equipment was demonstrated on a path from Algiers to Paris in July 1937, but apparently never used commercially.
Bernhard The "Bernhard" radio navigation system was developed to counter the Allied jamming that made the earlier "Knickebein" beam navigation system unusable. Bernhard and the companion "Bernhardine" and "Hermine" receivers were developed by Telefunken and first deployed in 1941. This system used Hellschreiber technology to transmit the current azimuth of a huge rotating antenna, as it rotated. The small "Bernadine" receiver printed the bearing to the ground station on paper tape in the aircraft twice per minute, at a range of 400 km with an accuracy of ±1°. As well as having remarkable accuracy, later improved to ±0.5°, this system, unlike "Knickebein", used a rotating beam which gave no clue as to the course of the aircraft using it.
Hell Myths and Legends A number of stories have gone around about the magic of Hellschreibers, their history, and their performance in the field. Are they true? The wartime Feldfernschreiber was used to transmit Enigma coded messages. It was common for troops at the front to send messages back to base using a Felsdchreiber and radio transmitter with only a barbed-wire fence antenna. During WWII the 6th German Army at Stalingrad was completely surrounded by the Russians, and the only link back to Hitler's headquarters was a radio Hellschreiber link. Stan Cook G5XB claimed in an article in Radio Communication 1981 to have built a Feldschreiber receiver from Meccano (an Erector-like construction kit) as early as 1942. (Stan apparently worked for the BBC during the war, receiving German Hell signals at their Beaconsfield receiving station). The Japanese built copies of the Hellschreiber machine which they used during WWII (Sony did make 10 - 20 units from about 1947 - see the interview with Nobutoshi Kihara).

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