Robert11 wrote:
I understand that fm signals in the 150 MHz and higher range propagate
pretty much as line of sight.

Yes. (there is some limited refraction)

But, is this also true for AM signals in this frequency range ?

Yes.

It's the frequency of the signal that determines what path that signal
will follow to get from Point A to Point B. Signals on nearby
frequencies will follow the same path.

So, a "dead air" signal - a pure, unmodulated signal carrying no
intelligence - transmitted on 150MHz will cover a given path. If you
adjust the transmitter to 149.9MHz, the signal will cover the same path;
likewise if you adjust it to 150.2MHz.

Now, if you put some information on this signal... if you use FM, the
information - the voice, or data, or whatever - causes the frequency of
the signal to vary between limits. Say, between 149.95 and 150.05MHz.
The signal will cover the same path as it did when it wasn't carrying
any information at all.

If you use AM instead... the signal will still spread out near 150MHz.
It'll spread out over a narrower range, maybe between 149.995 and
150.005MHz. Still, since the frequency at any given moment is still
pretty close to 150MHz, the signal will follow the same path.

--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com