Then I abandonned software
timing by using an external interface (a PIC) on the serial port and
ended up with something very similar to the VE2IQ I/F.

A few days ago I was thinking on how to generate a programmable
frequency for an MFSK scheme (I did post a message on this reflector),
and the DDS was one the possibilities. Thinking again at it, after all we just
need the high order bit of the phase accumulator, as the TX is driven with a
square wave. This makes the DAC completely unnecessary.
Would it be possible then to implement a 32-bit phase accumulator with
a PIC, to generate a frequency on the 137 kHz band ?
My knowledge of PICs is quite limited, any PIC guru with an answer ?
If positive, then it would be possible to make a really inexpensive outboard
generator for such an MFSK modulation scheme.

73  Alberto   I2PHD