-- 
Have Fun,

Brooke Clarke
https://www.PRC68.com
axioms:
1. The extent to which you can fix or improve something will be limited by how well you understand how it works.
2. Everybody, with no exceptions, holds false beliefs.

Date: Tue, 28 Oct 2025 15:11:35 -0400
From: Nick England <[email protected]>
To: Greenkeys <[email protected]>
Subject: [GreenKeys] 1949 time division multiplex demo
Message-ID:
	<CAB55hNcZ46hJJsbXptVk1UtRiGhW-Z-vOu0amGBYxoEJuXapDg@mail.gmail.com>
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https://www.navy-radio.com/rtty/fgc5/fgc5-proto-4901.jpg

photo caption - Electronic Time Division Multiplex Unit with attached
battery of four Teletype transmitters. The Electronic Time Division
Multiplex rearranges the output of two to four teletype machines so that
the signals originated by those machines are transmitted over a single
radio channel by a single radio transmitter, simultaneously for all
practical purposes. The apparatus is divided into transmitting and
receiving units. As messages are fed into a battery of four teletype
transmitters hooked into the ETDM each is compressed in time, sorted into
the proper time channel, mixed with the other signals, and fed into the
radio transmitter. At the receiving end, the process is reversed and the
signals, unscrambled, are fed into the teletype printers essentially at the
same time as they are transmitted. Since each teletype transmitter can send
 at speeds of 75 words per minute, this means a total of 300 words per
minute transmitted. The Electronic Time Division Multiplex is calculated to
make the best possible use of available radio frequency channels in
military operations.

The sign in the photo says that it is being tested on a 6000 mile RTTY loop
DC-SF-DC.

More info on this AN/FGC-5 system is at
https://www.navy-radio.com/rtty-mux-fgc5.htm

Nick England K4NYW
Chapel Hill NC
www.navy-radio.com