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how the heck does FM work,? (self.askelectronics)

submitted 4 months ago by Grumpydaddy to c/[email protected]

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Kind of an ELI5, but I tune a radion into a specific frequency to listen to a station. If that frequency is constantly being modulated (changed), how is the radio not going in and out of tune? I expect it is finding a way to measure multiple frequencies around the tuned station and decodes the data from it's deviation from the tuned frequency?

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[–] [email protected] 13 points 4 months ago

The FM tuner is a narrow band pass filter centered at the carrier frequency - it doesn't try to track the modulation. The FM demodulator then uses a VCO (voltage controlled oscillator) with a phase detector in a feedback loop, so that the output of the VCO tracks the modulated input signal. The input to the VCO then represents the baseband (demodulated) signal.