[GreenKeys] RTTY receiver noise immunity?

[Harold Hallikainen]

The TU-170 just compares the level of either tone to a threshold. If
either is above the threshold, mark hold is released. This is also used
for autostart.

It would be interesting for it, instead, to look for a difference in tone
levels. Noise should be about the same, while valid RTTY would have
substantial difference in tone levels.

Once you move to software, you could look for framing errors. If there are
above a certain percentage of characters with framing errors, it's
probably garbage.

I remember a bpsk demodulator that would just keep flipping the phase on a
frame error hoping to get it right eventually.

Harold



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