[GreenKeys] Northern Radio 152/2

[Duncan Brown]

The MD-522 AFSK modem used in the AN/GRC-142 (successor to the AN/GRC-26 
& -46) operates at 85 or 850Hz shift.  There is an option to run 
in-channel diversity with two 85 Hz signals spaced out in the normal SSB 
audio passband. Another option is voice-plus-RATT:  The 85Hz AFSK signal 
is centered around 2805 Hz (as I remember) and notched out of the 
speaker RX audio.  This way you get a TTY circuit plus voice order wire 
in one voice channel.

I think you would need a strong & stable (frequency) signal for 85 Hz 
shift to work well.

I've never heard of 240Hz shift, either.  The AWA Museum has a Collins 
diversity FSK converter that will operate on 425, 600,  or 850 Hz shift. 
I had never heard of 600 Hz shift before.

Duncan
K2OEQ


On 21-Jun-15 20:08, Jim Haynes wrote:
> 85 Hz shift is standard for carrier telegraph systems up to 75 baud.
> Transmitting a bunch of channels on either a voice grade wire line or on
> a SSB voice grade radio circuit.
>
> At one time some of the MARS services also required that shift be either
> 850 or 85, no 170 or other shift allowed.
>
> I've never been able to try 85 Hz for single-channel RTTY, but would
> like to.
>
> I don't know anything about 240 Hz shift - maybe that was for higher
> telegraph speeds.
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