Feld-Hell
This is a very old modulation type, invented in 1929 by a German
engineer, Rudolf Hell.
It is somewhat similar to the yesterday matrix printers, because each character is
made by a 14 rows x 7 columns dots matrix, where the columns are
scanned left to right and each column bottom to top.
Each dot is transmitted as 8.163 milliseconds of carrier or, if there is white space, 8.163 milliseconds of
silence, with the transmitter shut off. This makes Feld-Hell, also called Hellschreiber, quite similar
to CW and the same narrow filters can be used. The effective speed is thus
122.5 baud and there were also machines working at 245 baud.
Nowadays nobody uses mechanical equipments, but it is easy to transmit and receive Feld-Hell using
a computer and a standard audio card, with an SSB transceiver.
A unique feature of this old/new mode is that the transmitting side needs character fonts (not codes)
and the receiver can read whatever was transmitted. Thus it's easy to transmit characters of
whatever language, including chinese, japanese etc., or even custom drawings, without any modification
on the receiving side.
Moreover, the recognition of characters on screen is fuzzy, because is done by your eyes. Thus, is some
dots are wrong or disturbed, normally you can keep understanding the character and the whole message.
The Siemens A2 was built in 14,000 copies and
used exensively during World War II by the German army.
After the war it was used by Czech and Swedish armies
up to the sixties.
A QSO in Feld-Hell, that I received
using the program Hellschreiber, written by IZ8BLY.
Another QSO received with the same equipment. Please
note the duplicated rows, used to avoid syncro problems among
the different stations. This solutions was used also
on the original electromechanical equipment.
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