[GreenKeys] TGC-1

[Jim Haynes]

Thanks for the detailed explanation of how that system operated.

I'll add one comment from one who was not involved in that kind of
work at all.  As you say, the AN/TGC-1 was awkward in having the
transmit and receive machinery in the same cabinet.  However the
advantage of this was to make it very easy to move or rearrange
or expand or contract a message relay center, since you just put
in a TGC-1 for each telegraph line you need to handle.

Other kinds of torn-tape message centers had all the receivers
grouped in an aisle and all the transmitters grouped in another.
There was a six-headed TD as well as a 3-headed one made for this
purpose.  And the disadvantage is that it is harder to build and
configure a message center, so this would be used where a message
center was more likely to stay put.

These systems were used in commercial telegraphy as well as in
military systems.  Postal Telegraph Co., the pre-WW-II competitor
to Western Union, had such a system.  In theirs the multiple sending
TDs did not send directly to the outgoing lines, but were buffered
from them by a stage of reperforators and TDs.  This was so that if
traffic for a destination was heavy it would be buffer stored beyond
the TDs that the operators were feeding.

It was common to have a pair of TDs feeding the same destination, each
one starting when the other stopped.  This was sometimes called flip-flop
operation.  I have a relay box I found on ebay with the Postal Telegraph
nameplate on it and appears to be designed for just that operation,
as there are pairs of relays wired so that only one of the pair can be
energized at any one time.