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August 18th 04, 06:39 AM

In article ,
(Clay Denski) wrote:

I have a very technical fundamental question about how radio works.
And no, I'm not ignorant of physics or the basics (I don't think,
anyway).. Here goes:

Say you have for simplicity two radio stations (AM for simplicity).
One is talk radio and the other plays Led Zeppelin all day. I
understand that "Talk" uses a different carrier frequency than
"Zeppelin" and that this allows my radio to tune in and detect one
without the other interfering. I also understand how a carrier wave
is modulated in AM and FM..

BUT, what I don't get is why the two do not interfere. Let me
explain.. Take a timeslice of EM radiation hitting my recieving
antenna at some moment. Some electrons in the antenna move up in
response to experiencing some energy from "Talk" station that
corresponds to a high point in the sine-wave. The same electron,
though, is pulled down a bit in response to some EM hitting it from
"Zeppelin". How does "Talk" not affect "Zeppelin" if both are shoving
the same electron in my antenna? How does my radio figure out that an
effect at the antenna is NOT an ordinary modulation of the "Talk"
carrier wave but rather of some other one and therefore to be ignored?

Thanks for answers folks!

The induced "Talk" electrons are separate from the "Zeppelin" electrons.
The two different EM waves generate two different RF currents or two
different flows of electrons in the antenna wire. If you look at the
generated voltage on the wire with a oscilloscope in the time domain
then you are going to see the sum of both generated RF currents.
However, if you looked at it with a spectrum analyzer you would still
see them as separate signals in the frequency domain. The radio receiver
is designed to see one narrow band of frequencies at a time so only one
of the two is received while the other is rejected.

--
Telamon
Ventura, California

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