[GreenKeys] Differences between US Army & Navy TTY communications

[Duncan Brown]

In digging into a M28 ASR, I think I have stumbled across some of the 
differences between Army & Navy TTY communications.  All the schematics 
for M28 KSR & ASR units that I have seen, show just one loop, tying the 
TX & RX circuits together. (Aux reperf in a M28 ASR typically has its 
own loop.)  M28s are wired such that they are very flexible and can be 
wired to separate TX & RX circuits, but that is typically not how they 
are shown on system drawings.  Th AN/UGC-6 (M28ASR w/aux reperf) 
schematic (fig 12-38 from the Navy manual ) does not show an option for 
full duplex (separate TX & RX loops) operation.

Nick says that full duplex was not used much (if any) in the Navy TTY 
comms, but his page, https://www.navy-radio.com/circuits.htm does 
mention full-duplex operation.

In 1950, the Army (and Army-Air Force) started buying Kleinschmidt 
equipment exclusively (although they did buy some  M28s later.)  All the 
Kleinschmidt units, TT-4, TT-76, TT-98, AN/FGC-25 were set up for full 
duplex operation with separate cables or jacks for TX & RX. The standard 
Army wire-line modems (TH-5 & TH-22) used with the TTYs were capable of 
both simplex (2-wire) and full duplex (4-wire) operation.  Mobile RTTY 
huts (AN/GRC-26, -46, -122) could all be operated full duplex, though 
simplex was the norm. (the AN/GRC-142 is a simplex GRC-122.)

I was a TTY repairman in the Army Security Agency. In Viet Nam in 1967. 
I was in the 337th Radio Research Co., supporting the 1st Infantry 
Division. We were located near the Division HQ and had outstations 
(AN/GRC-46 huts) positioned with the forward located 1st ID Brigades.  
We also had a link to our battalion HQ and that link carried a lot of 
traffic; so much so that it was run in full duplex mode, with messages 
going in both directions, simultaneously.

The outstations had tape facilities (TT-76s), but our company comm 
center just consisted of a hut (AN/MSA-?) with four TT-4 printers, 4-5 
KW-7 crypto units and four TH-5 modems in it. So all outgoing messages 
had to be typed on-line.  Imagine typing a message on a printer while 
another message is being printed!

The Army did have medium-sized comm centers in trailers or vans and big, 
fixed station comm stations, but I never saw them. I did work on a 12 
channel tape-relay center that was in a 38 ft trailer..

So maybe some of the difference between Army & Navy operation was due to 
the Army units being smaller and more spread out; vs. the Navy with 
concentrations of operations on big ships. The Navy's use of multiplexed 
RTTY may have given them enough channels that they did not need to 
operate full-duplex.

Just some thoughts.

Have fun,

Duncan
K2OEQ
31J30



On 08-Apr-23 16:24, Nick England wrote:
> See also
> https://www.navy-radio.com/circuits.htm
>
>
> On Sat, Apr 8, 2023 at 4:13 PM Nick England <navy.radio at gmail.com> wrote:
>
>     They just weren’t used in full duplex (except if the aux typing
>     reperf was independently connected). Normal installation was to
>     the C-1004 box that you manually switched from CFS REC to CFS
>     SEND. (The TONE position was for hookups that automatically keyed
>     the xcvr, usually UHF).
>     https://www.navy-radio.com/rtty/c1004.htm
>
>     I guess I just don’t understand when you would run full duplex
>     using a single TTY.
>     If you wanted to receive while transmitting you just used an
>     additional TTY printer or reperf.
>
>     Read more about the Navy’s view of RATT
>     https://www.navy-radio.com/journal.htm
>
>     And
>     https://www.navy-radio.com/commsta/circuit/THE20GOLF20SYSTEM.jpg
>
>
>
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