I have an MTR-3000 VHF and interfaced it to the VOTER board. First keyup, horrendous noise on the TX. I decided to put in a voltage divider on the input and use the high voltage on the output op amp. The noise is still there but more subtle(I really want good TX audio). I tried 3 different VOTER boards thinking it was an assembly issue. Anyone know what this noise is from? Almost sounds like its oscillating. I am using the 25 pin connector to feed audio to pin 22 and gnd to pin 18. I tried changing TX to pin 1 and moving the audio gnd to pin 9 and same noise. Sounds like a bad imitation of a British dial tone. If there is a better, way, I am all ears. Thanks,
Since moving the tx audio to pin 1, I needed to switch asterisk to pre emph the audio by turning on a tone in the voter.conf. That code needs some love. Anyway after doing that I turned the tx tone off on CPS and the noise vanished.
I was using pin 22 before because it sounded best with the PAUL interface.
I will need to undo my modifications to the output of the voter too, I padded it heavily and used the rail voltage on the op amp with jp3 set to 2-3. I did that to get the voter audio up and the noise to a minimum. But after a few months I couldn't stand to hear it in the background anymore.