[GreenKeys] RTTY in WW-II

[Jim Haynes]

As Duncan says, the best-known WW-II FSK system used the AN/FGC-1 dual
diversity FSK converter.  This is a Western Electric item in a 7 foot tall
cabinet, built telephone style, which is to say flat panels in the rack
with the parts sticking out the front, rather than panel-and-chassis
construction.  These were sometimes used with the companion receiver
AN/FRR-3 of similar construction, but also with more ordinary receivers.

The transmitter technology of the time usually involved a 200 KHz
oscillator that was frequency modulated by a reactance tube and then
beat against a crystal or VFO to get the desired output frequency, or
a sub-multiple thereof.

Press Wireless Co. was using RTTY in WW-II and their work is documented
in the November 1944 issue of Electronics magazine.

The standard shift in those days was 850Hz.  This was used not because
the signaling speed demanded it, but to accomodate the drifty transmitters
and receivers of those days.  Even then there was some use of AFC in
receivers to compensate for the drift and make it unnecessary to have
an operator constantly retuning the receiver.

There is an article in Communications magazine for September 1946 about
the AACS (Army Airways Communications Systems) used during the war for
weather transmission.  The writer mentions that 850 Hz shift was used,
but that some other units used shifts of 170 and 340 Hz.  He says that
at first they used Hammarlund Super-Pro receivers with an external HF
oscillator common to both, but that they were later replaced with Wilcox
and Press Wireless equipment.  He shows a block diagram of the receiver,
including the tube types used.

Now if you want some ancient history, there is an article "Teletype Now
Used on Radio Circuits to Hawaii by R.C.A. Communications, Inc., for
All Its Messages" in Telegraph and Telephone Age for Oct 1, 1932.
and "Application of Printing Telegraph to Long-Wave Radio Circuits" in
Bell System Technical Journal for October 1931.

"Printing Telegraph by Radio" in Journal of the Franklin Institute,
January 1922.

"Multi-Channel Two-Tone Radio Telegraphy" in Bell Laboratories Record,
December 1946.

"Frequency-Shift Radio Teletype in World War II" Bell Laboratories Record,
December 1947.

There was even time-division multiplex way back then.  "Time-Division
Multiplex in Radiotelegraphic Practice" Proceedings of the IRE,
January 1938.


jhhaynes at earthlink dot net