"Mark" wrote in message
m.

The sidebands do look like FM. They also look like IM which I presume
you are calling AM.

Agreed

Note that both FM and AM produce symmetrical sidebands.

Agreed.

However when both AM and FM are present together, the
combination usually produces asymmetrical sidebands. This is because
the AM and FM sidebands have different phases above and below the
carrier. Since the sidebands in your experiment look pretty
symmetrical I would say that if AM and FM are present together, they
are not close to equal.

Agreed.

If they were close to equal, the sidebands would be very asymmetrical.

Agreed.

So how do we tell if the sidebands are FM or AM?

Suggestion. Send the signal through a 4 kHz BPF that is wide enough
to pass the sidebands but not wide enough to pass the 50 Hz or it's
harmonics.

That's an idea.

You should then be able to analyze this BP signal to see
if it is AM or FM. If it is AM, the envelope will vary at 50 Hz. If
it is FM, the envelope will be constant.

Its a mixture. Now the fun begins. There is an envelope, quite clearly at 50
Hz.

However, if we limit it heavily to forcably eliminate the envelope, there
are still 4 sidebands left.