Hi, Lynn

The oscilloscope monitor on an A.M. transmitter output
doesn't show the carrier (except during periods
of no modulation). The scope shows the resultant
of the carrier and both sidebands added together vectorially.
A spectrum analyzer would show a constant amplitude carrier
in the center of the A.M. spectrum.

There is a good description of the process at the Agilent site.
Google a.m. phasor diagram
Click on "Spectrum analysis AM and FM HP T&M Application Note 150-1"
Beginning on page 48 of the pdf file is a description of the a.m.
spectrum, based on phasor diagrams.

73,
Ed Knobloch

Lynn Coffelt wrote:
Wohoooo here, maybe, since I caught this thread in mid stream, I am out
of place, but Don, your last sentence, "Do remember that the carrier
amplitude does NOT vary with modulation." doesn't sound like high level
amplitude modulation.

When I was young(er), amplitude modulation meant exactly that: carrier
amplitude varying with modulation. In fact, when working out the bugs of
home designed and built AM transmitters, one favorite test was with an
oscilloscope, measuring the amplitude of the carrier, making sure that the
carrier amplitude did actually approach zero and rise to twice the
unmodulated carrier level. (voltage, not power, of course)

Now, for sure, the carrier average POWER didn't vary (much), but the
audio power was added. Now, PEP, peak envelope power, is a whole different
thing for us old timers, and maybe that's what is being discussed here. In
that case, please excuse Mr. Buttinski!

Old Chief Lynn, W7LTQ