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Why is it spelled...?

What do the AM and FM mean in radio?
AM is an acronym for "amplitude modulation"; FM is an acronym for "frequency modulation." When an AM radio signal is broadcast, a steady carrier wave is sent out, and the message that is being broadcast is carried on the carrier wave by modulating, or varying, the amplitude of the carrier wave -- that is, the vertical size of the wave, top to bottom. In FM radio the message is carried by modulating, or varying, the frequency of the carrier wave -- that is, the number of cycles, or repetitions, of the wave per unit of time. (The frequency of the carrier wave is what the numbers refer to on your radio dial.) One advantage of FM is that unwanted noise, or interference, affects the amplitude of the carrier wave but not the frequency. So FM comes through with less static.
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