Some FM chips might have a pin to provide signal strength indicators by
measuring saturation of the IF, but I have never seen this line controlling
the gain of the RF. Don't forget, we're talking about a Part 15 transmitter
outputting in the milliwatts, and I can't see this level coming anywhere
close to overloading the input. And even if there were ample RF energy, it
would probably overload every stage of the receiver and do more harm of
environmental exposure rather than attenuating the audio level because of
IMD. I've taken a walkman up to the base of a 50,000 watt FM tower and never
had an audio attenuation problem unless I was listening to an adjacent
channel. ;-)

If you reference me to a domestic (consumer type) FM receiver model with AGC,
I would like to know so I can change my statement as to never seeing an FM
AGC circuit.

Rick

"Alan B. Pearce" wrote:

> >I've never seen an FM receiver with AGC. RF intensity
> >should have no effect on FM audio levels. AM however,
> >this would be true. FM receivers do have AFC to
> >keep the receiver from loosing lock.
>
> Post mixer I would agree with you, but I have seen gain control on the RF
> stage to get good IM performance. I seem to recall some early FM IF chips
> had a signal strength output to do this.
>
> If there is no AGC at all that may even exacerbate the problem if he is
> feeding a very strong signal into the receiver. The IM resultant may be
> producing a similar problem.
>
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