[RTTY] MMTTY receive problems

[Richard Ferch]

Jim,

>From your description it is likely that there is nothing you can do inside
MMTTY. At least, it sounds to me as if the AGC in your receiver is knocking
down the strength of the signal before it ever gets to MMTTY. If that is the
case, what you want to do is put the offending strong signal outside your
receiver's IF bandpass.

If you are transmitting using FSK (keying from TxD in MMTTY) you can't move
your audio frequency, but you can use your radio's IF SHIFT or IF WIDTH or
similar controls to block out the offending signal, assuming you have narrow
filters inside your receiver's AGC loop, such as crystal filters in the IF.
Audio DSP filters outside the AGC loop (just like the ones inside MMTTY)
won't do any good, because the goal is to stop the AGC from reacting to the
unwanted signal, not to filter it out after the damage is done.

If you are using AFSK (using the sound card to transmit) you have the
additional possibility of tuning your radio so that the desired signal is
near the edge of your radio's bandpass and the strong unwanted signal is
outside the bandpass. Depending on which side the strong signal is on, that
may mean tuning near the upper or the lower edge. That should at least knock
the big signal down far enough to keep the AGC from killing the wanted
signal. If that still doesn't work, you may have to resort to turning the
AGC off, backing off the RF GAIN control, or other measures to try to keep
the strong signal from desensing your receiver.

Hope this helps.

73,
Rich VE3IAY