Chris, here's a question for you. (I'm assuming that you are working
with FSK TTY.)

Is the classic 850-Hz shift still the current standard as it was during
the 1960s when I was still involved in TTY? I had thought that it had
been reduced to something like 75-Hz during the 70s due to the problems
with propagation path differences over a 850-Hz frequency spread.

Also, back in the mid-60s, it was sort of presumed that AFSK would soon
replace FSK... Did that ever actually happen?

By the way, in those days we tested our terminal units by printing NSS
transmissions for hour after hour. You could then visually scan down
the pages of printed code groups to determine how often your system
produced a glitch.

I was then among the more fortunate, because I owned a Model 26 TTY, a
model 14 Transmitter/Distributor, plus the holy of all holys, a Model
14 typing reperforator. Today all of these have been replaced by
computers! :-) Still, hearing those old machines hammer and click
away provided much more gratification than does a computer!

Have fun, Harry C.