"Radium" wrote in message
ups.com...
On Jun 30, 3:46 pm, Jeff Liebermann wrote:

With AM, it's ALWAYS the high frequency
that acts as the carrier
and the lower that acts as the modulation.

In AM, isn't the carrier the signal which always maintains a constant
frequency and only varies by amplitude?

If a carrier signal varies by anything other than just amplitude, then
it isn't AM. Right?


Essentially correct. The sidebands either side of the central carrier wave
contain the modulation information.

If the carrier wave were to shift in frequency then that would be frequency
modulation.

Before you ask, yes it is possible to have an AM signal modulating an FM one
and several other wonderful combinations involving phase transformations,
variable pulse widths and sideband(s) only. It is all detailed in the ARRL
Handbook, RSGB Handbook and many other prestigious publications.

Mike G0ULI