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#8
August 18th 04, 06:24 PM
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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. 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. 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. -- It's unfair to characterize Kerry as a flip-flopper. He's consistently in favor of marrying a rich widow and buying your way into the White House. -- Rex Tincher |
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