[GreenKeys] Old Army Portable Communication Truck

[Duncan Brown]

Roy,

I don't remember seeing anything in the AN/GRC-46 manual about 
simultaneous voice and RTTY and was surprised at the mention of it in 
the film.  But the T-195 is AM and you could probably talk and send RTTY 
at the same time (the T-195 used true FSK).  On the receive side, you 
might hear a little low frequency "hum" from the FSK; and the FSK 
converter (being FM) would strip off most of the AM and probably copy 
the TTY signal OK.  The voice "circuit" was probably just used for 
"order wire" while the TTY was the major circuit.

This was before the Army had SSB radios and ISB was not typically used 
in tactical communications systems.  The AN/GRC-46 was replaced starting 
in the mid /late 1960s with the AN/GRC-122 & -142. It was SSB and was 
modulated by an AFSK signal for RTTY. It did have a "Voice plus TTY" 
mode.  It was done by using 85 hz shift at the high end of the audio 
spectrum (around 2800 hz as I remember). But no ISB.

have fun,

Duncan, K2OEQ
USASA 31J


On 05-Feb-12 17:33, Roy Morgan wrote:
>
> Greenkeyers,
>
> I watched that movie.. learned a bit, not having every used any of the
> gear shown.
>
>
> AN/GRC-36
> The movie says that simultaneous voice and RTTY signals can be carried
> by one RF signal, but it does not say if it is independent sideband
> operation, or if the FSK and voice (AM) are put on the same carrier.
> Anyone know?
>
> The movie shows the operator running the CW key left handed!
>
> Roy
>
> Roy Morgan
> k1lky at earthlink.net
> K1LKY Since 1958 - Keep 'em Glowing!
>
>
>
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