[RTTY] A thought on FSK timing

[aflowers at frontiernet.net]

Peter's question about 75-baud brought to mind something I've been pondering for a while....I'm not convinced that the "MMTTY + UART" is always optimal from a timing perspective, though it probably is much better than EXTFSK by itself.  The question in my mind is that since MMTTY is pacing the characters every ~165ms you are still at the mercy of it's timing jitter at the character level. There are more than a handful of people with strange or varying stop bits, including many big-gun contesters.  My hunch is that this is a result of MMTTY's "pacing" not being completely stable or accurate in some systems or configurations out there in the wild, but maybe it's something else.  Surely this matters to pseudo-synchronous demodulators that rely on tracking the start-stop bit timing to get a bit more SNR than asynchronous demodulators. I suppose how much is going to depend on the demodulator implementation at the receiving end.
 
Anyway, I'm curious if anyone has another explanation for the funny-stop-bit phenomenon.
 
Andy K0SM/2