Hell - Schreiber

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überarbeitet am 13.5.2013

When it turned out, that many of the morse code wireless operators of the Swiss Signal Troops were too slow in transmitting messages, the Signal Troop Command decided to introduce the Siemens Hell printer system in the high power stations.
Because the performance of the receiver Lorenz Eo509/I used in the G1,5K-Station was too poor for reliable transmission results, and because of unexperiences wireless operators, the Siemens Hell printer system was faded out after a few years and was replaced by the Moser Baer high speed telegraphy system. But as even this technique required sufficient knowledge of morse code for the transcription of the printed morse code stripes, the Signals Command decided to revert to simple morse code operation and improved the porse code training of the signalmen.

It was not before the introduction of the ETK printer and the much improved KFF 58, when the Swiss Army returned to printed plain text message transmission.

Siemens Hell printer

Rudolf Hell developed the Hell printer System in the year 1929, the Hell printers produced by Siemens & Halske found widespread use for press and financial informations transmissions in Germany. The messages on a punched paper tape are coded by the Hell transmitter in a 7x7 dot matrix, the coded audio signal is fed to the transmitter.
The audio signal coming from the receivers audio output is amplified and fed to the Hell printer. A printing spindle prints the letter twice on a paper tape. If the synchronisation is failing the text is printed diagonally, the synchronisation has to be corrected until the text lines are horizontal. But even if the synchronisation is not optimal, the message is still legible. This is even the case, when single dots are failing due to poor propagation conditions, in contrast to teleprinters using the Baudot code.
This is the reason that the Hell system was quite popular because of its good reliability even under poor propagation conditions.

Handlocher The messages are transferred to a punched paper tape with the "Handlocher", a manually operated tape puncher.
Hell - Lochstreifenleser The punched paper tapes are read with the "Lochstreifenleser" to generate the Hell audio signal.
Röhrensummer An audio frequency signal of 900 Hz from a "Röhrensummer" (an audio frequency generator) is superimposed to the signal which is fed to the transmitter. It is rectified and modulates the transmitter output via the control grid of the modulator tube, the signal itself is unmodulated.
Hell - Schreibverstärker The signal has to be converted back to an audio signal by means of a beat frequency oscillator of the receiver. When operated with the slightly outdated Lorenz Eo509/I receiver of the G1,5K, a heterodyne had to be generated with adjusting the reaction control of the receiver over the point of self-oscillation.
This audio signal then will be amplified in the "Schreibverstärker" (printer amplifier) and fed to the Hell printer.
Hell - Schreiber A double printing spindle will be pressed to the paper tape using a solenoid, the message will be printed in two identical lines which run horizontally in parallel when the printer is in synchronisation.
With poor speed synchronisation, the message is still legible, but the two lines are oblique. The speed can be adjusted using the speed control until synchronisation is reached and the two lines are in parallel.

The high power wireless stations G1,5K, G3L and C-Station of the Swiss Army were equipped with Hell printers after 1935. Because of quite poor performance of the Lorenz receivers used of the lack of experienced wireless operators, the use of Hell mode turned out to be unreliable and the transmission mode was abandoned in 1944 and the decision was made to improve morse code skills of the wireless operators. The Hell printers have been withdrawm from the stations in 1944.

The Hell system shown on the images was demonstrated at the Uster Day of IgUem in full operation, many thanks to Werner Gebauer for some original printed tapes.

further literature:
d: Das Fernmeldematerial der Schweizerischen Armee, Band 14, Die Endgeräte vom Morseschreiber bis zum Laptop, Merker Verlag, Luzern

© Martin Bösch 23.5.2013