In article ,
"Ron Baker, Pluralitas!" wrote:

--snippage--

That doesn't explain why the effect would come and go.

I don't understand what effect you're referring to here.

When I was tuned to the 3rd harmonic sometimes
I would hear it and sometimes not.
It would come and go rather abruptly. It didn't seem
to be gradual fading.

Especially if the RF field is strong, there are a lot of mechanisms
which can create harmonics after the signal leaves the transmitter --
rusty fencing, or tooth fillings, for example. I can see how one of
those could be intermittent.

But once again you have surprised me.
Your explanation of the non-multiplied sidebands,
while qualitative and incomplete, is sound.

I'm a physicist/engineer, and have been for a long time. I have always

The you understand Fourier transforms and convolution.

I suppose so; I've spent over fifteen years poking around in the
entrails of MPEG...

I don't understand what you are saying here either. And in my
experience, the term "modulation index" is more likely to show up in a
discussion of FM or PM than AM; are you using it interchangeably with
"modulation percentage"?

As I suspected -- just different words for the same thing.

So:

It looks to me that the tripple frequency sidebands
are there but the basic sidebands dominate.
Especially at lower modulation indexes.

With well-designed gear (or theoretically), for AM there will be no
other frequencies present except for the carrier and the ones
represented by the Fourier spectrum of the modulation -- one set either
side of the carrier. That is only true, of course, as long as there is
no overmodulation; that creates a *lot* of other junk, because there are
periods where the carrier is entirely cut off.

So I still don't understand what you mean by "triple frequency
sidebands" or "basic sidebands".

As I said in another post, modulation is a "rate effect", so there never
should be any frequencies generated at multiples of the sidebands
surrounding the fundamental; instead they are always identically as far
from the harmonics as they are from the fundamental. Is that what you
are calling "triple frequency sidebands"?

Isaac