[RTTY] MMTTY, permanently disable AFC

[Joe Subich, W4TV]

On 2014-06-17 1:07 PM, Bill Turner wrote:
> A further complication with MMTTY is when AFC is on, the Mark tone
> tends to wander around with no signal present. This can be a problem
> when S&P'ing because as you tune across the band with AFC on, it will
> reach out and lock on to a signal before the signal is correctly
> tuned in.

Again, there is a solution to this if one takes time to study the MMTTY
documentation (help files).  AFC (on the AFC/ATC/PLL tab) has a "SQ"
setting - the default is 32.  By setting SQ higher AFC will not lock
on/track weaker signals (noise) while setting SQ too low will result in
AFC wandering with noise.

There is some interaction with digital AGC (Limit Amp on the Demodulator
tab), the audio level going into the sound card, and sound card gain.  I
generally reduce AGC from 200 to 100 and set audio into the sound card
so the noise is just visible on the audio spectrum (FFT) with View | FFT
Sensitivity set to Low with the antenna connected and just noise (no
signal) on a given band.  Coupled with a limited AFC range and a higher
than default SQ setting, AFC behavior is quite good (and tends to mimic
that of 2-Tone) for FSK operation (fine tuning only) in both S&P and
Run.

73,

    ... Joe, W4TV