In article ,
clifto wrote:
Telamon wrote:
(Clay Denski) wrote:
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?
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.
"Pushing the electrons" is a red herring. All electromagnetic and
electrostatic forces in the universe contribute to pushing those
electrons. Remember that those electrons come from your antenna wire,
not the distant forces; the forces move *your* electrons, they don't
send electrons to your antenna.
Where did I say that the electrons came from the EM wave? I used the
word "induced." This discussion is about two forces acting on electrons
in a wire. Let's not make it more complicated than necessary to convey
the concept of how they simultaneously interact.
Remember also that electricity isn't electrons, it's a flow of energy
that can move electrons. So it's not necessarily the electron movement
that we're interested in, it's the flow. Overquantize this concept and
you won't recognize the forest because you're looking at a few trees.
DC or AC a "current" is a flow or movement of electrons.
Two stations, "Talk" and "Zeppelin", induce flows of two different
frequencies in your antenna. We use the principle of resonance to
separate them; we tune a resonant tuned circuit to one frequency or
the other. Hold a 600 Hz tuning fork to an electric razor, and if
there's any 600 Hz component in the vibration the tuning fork will
show the principle; you'll hear 600 Hz louder than most other
frequencies in the resulting co-vibration. All the other frequencies
sort of disappear in the noise.
Tuned to "Talk", we get a whole lot of "Talk" frequency flow, just
like with the tuning fork. Other frequencies like "Zeppelin" aren't
resonated here; they get lost in the noise.
--
Telamon
Ventura, California