I will try this tonight. (lifting pin1 of audio IC chip to turn it off)
This noise is ONLY on AM
transmit only. SSB
is clean. Also RX
is clean, so this noise has got to be in the audio chip area, as looking at the schematics, the TA7222 chip is only for AM
audio, and the SSB
audio is diverted into the AN612 balanced moduator chip via TR21 (2sc945) AM
I know what you are wanting me to do, is turning off the audio chip circuit by removing the 13.8v going into it. Once thats turned off, and if the noise goes away, then we know its either the Audio chip or associated circuitry. If this "air" noise still persists then we would need to look towards the back end of the radio. But since it only happens in AM
mode, and the "mode switch" is before the final output stage, it MUST be in the AM
audio chip area.... because if the noise was also on SSB
, then we could rule in the output section....
Will let you know more later tonight.....
I think we are onto something here....