Ive been asked this several times recently - why go to all the trouble of taking control of the PRC-320s synthesiser, with all the attended difficulties of isolating the decade switches when in remote etc, rather than simply replacing the sythesiser in its entirety with an AD9850 or Si5351 DDS module and Arduino controller?
So i'll explain. Yes, I could remove the synthesier module 9, and VFO unit 3h and replace it with a DDS, using the Arduino to read the decade switches directly....
... and the radio will never work properly again!
Sadly, study of the service manuals reveals that the synthesiser not only controls the VFO, but it also provides the variable control voltages that tune the RF stages, generate the out of lock tones, phase error outputs etc. Recreating those control voltages would likely be a very difficult task. I suppose it could be done, but its not something I have the time to do im afraid.
Im hoping the Arduino stuff arrives soon, as its about time I made a start with the control code anyway!