¿ªÔÆÌåÓýHere is a high-level explantion:
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Sound is nothing more than compressions and
decompressions of air.? Look at a speaker and?think of the way if
pulsates back and forth.? This is producing these compressions and
decompressions.? Since there is nothing to compress in a vacuum, sound
cannot travel through it.
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Electromagnetic waves are different.? These
are not compressions and decompressions (of air at least).? In fact, no-one
truly knows who the electromagnetic waves really work.? They can travel
through a vacuum at the speed of light (3 * 10^ 8 m/s).?
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Now, to get an idea of how sound is converted to
electrical impulses, think of this scenerio.? Think of a big woofer speaker
and remember how it works.? In its simplicity, it is a magnet moving back
and forth in a magnetic field.? Now reverse this and think of this woofer
as a microphone (although this would be a terrible microphone, but it
demonstrates the principle nevertheless).? As I talk into this woofer, I am
sending compresssions and decompressions of air which will move the woofer back
and forth.? This moving of the woofer, will cause the magnet to move back
and forth, thus generating alternating current.? This current is a
representation of sound.? You can amplify this and then send it back to
another speaker where it will produce the same back and forth movement and
therefore produce the same compressions and decompressions of air
(sound).
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Radio waves are?electromagnetic waves.? A
radio transmitter will simply take this alternating current and mix it up with
an electromagnetic wave.? AM is short for amplitude modulation, and FM
short for frequency modulation.? These are 2 different ways to combine AC
and an electromagnetic wave, there are more however.? The receiver will
then have to remove the electromagnetic?wave to recover the original AC
signal.?
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Bandwidth refers to the amount of data that can be
transmitted over a medium.? In this case, it would be the frequency range
(difference between highest and lowest frequencies transmitted).? I may be
wrong, but when someone refers to purchasing bandwidth, I think they are
referring to purchasing a licence to broadcast on a specific
frequency.
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Shaun Phelps
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? ----- Original Message -----
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