On Jun 30, 7:43 pm, Jeff Liebermann wrote:

The carrier does NOT vary in amplitude. If
it did, that would be modulating the carrier, which is the job of the
modulator, not whatever is producing the carrier.

Exactly. The modulator signal modulates the carrier wave. If there is
no modulator signal, then the carrier does not vary by amplitude or by
anything.

One poster stated that the signal with the higher-frequency is
automatically the carrier wave while the signal with the lower-
frequency is automatically the modulator wave. This is not true. What
I was trying to say is that an AM radio carrier wave cannot vary
significantly by anything other than its amplitude [though, as one
poster pointed out, the AM carrier can experience extremely-negligible
variations in frequency]. If an AM radio signal has that restriction,
it is the carrier wave. If an AM radio signal does not have that
restriction, then it is the modulator wave. This is true, even if the
AM carrier wave is of a lower-frequency than the modulator wave.
That's what I was trying to say.

In AM radio, determining which is the carrier wave and which is the
modulator wave is not by which has the higher frequency but rather by
which has the restriction that I stated.

If there is no modulator signal, then no carrier signal of any type
[AM, FM, etc.] will vary by any quality [frequency, amplitude, phase,
etc.]