"Giulia" wrote in message
...

OK... you have pin2 grounded for no input signal. Now use your scope
and trace backward from the RF output collector... moving back through
the audio chain... noting the origin of the 100Hz oscillation.
Normally those radios have only a single transistor buffer for the
mic... followed by a high power op amp (usually mounted to chassis
wrapper) for the audio. Your signal tracing should take long at all.
Hope that helps.

Changing in VR5 (some related to modulation) remove the noise ,
i put vr5 more near ground.

Noise seems generated from somewhere feedback at hight swr....
regulation of vr5 remove noise but what kind of effect can it have on
modulation (in am all semms right RF evelope in the scope and audio
received from another cb)?

Giulia

RF feedback into the microphone? If you feel it is due to high SWR - why not
check and reduce it? Try your tests again. What kind of mic are you using?
If you mentioned it, I didn't see it. I've seen D104s do that. On 2 meters -
I've seen RF get into the power source and do all kinds of weird things to
the signal.

Check your SWR then - go from there. IF it IS high, even if the mic/audio
issue isn't cured, at least another problem will be - and save you from yet
a future one.

Are you using an "Amplifier" with this set up?