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- AM and FM modulated signals for radio. amplitude modulation and frequency modulation are types of modulation . The electrical signal from program material, usually coming from a studio, is mixed with a carrier wave of a specific frequency, then broadcast. In the case of AM, this mixing is done by altering the amplitude of the carrier wave, proportional to the original signal. In contrast, in the case of FM, it is the carrier wave's frequency that is varied. A radio receiver contains a demodulator that extracts the original program material from the broadcast wave. (en)
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