[GreenKeys] ITTY 850 shift?

[Jim Haynes]

On Sat, 4 Feb 2023, Harold Hallikainen via GreenKeys wrote:
>
> Anyway, I think there may be advantages to 850 Hz shift with selective
> fading and dynamic threshold control.
>
See QST April 1996 pp 78-79 "The Case for Wide-Shift RTTY by
Brian Beezley K6STI.  Brian is the author of the original PC software
RTTY terminal, RITTY.

It's my belief, without any solid evidence, that 850 shift was originally
chosen to get some tolerance for frequency drift in radio equipment of the
1930s-50s.  170 Hz shift for amateur RTTY came into wide use when we got
better equipment, thanks to the needs of SSB operation.

In amateur service it was tolerable to carry on a QSO with one hand on
the receiver tuning knob; but in commercial/government/military service
there was a need for reception without manual intervention over a period
of hours at a time.