> Just out of curiosity, how are the existing tones generated? It's PWM
> from PTB6, right? Couldn't you just vary the min and max values up &
> down to control the volume, sort of a scaling concept...? Would that
> work? Should save adding hardware if it does...
They're PWM, trouble is it's only 16 levels. Adding level control there
means either reducing the resolution further, or stretching the PWM cycle
period and lowering the carrier frequency. Plus, all of the timing is tied
to the cycle time.
The BPSK modulator does manage to get by with a longer PWM period and 256
levels, and it's got a scaling system built in because of the need to do
envelope shaping. It's only doing 31.25 bps, though - I'm really not sure
the same thing will work at 1200 bps. I do intend to have another look at
it when I get a chance, though.