this post was submitted on 09 Jul 2024
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how the heck does FM work,? (lemmy.world)
submitted 4 months ago by Grumpydaddy@lemmy.world to c/askelectronics@discuss.tchncs.de
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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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[–] l_b_i@yiffit.net 9 points 4 months ago* (last edited 4 months ago)

RF only has 2 components, Phase (frequency) and its amplitude. For Analog FM radio, you have a center frequency you tune to. The variance from the center frequency (phase) is the amplitude of the carried signal. For digital signals, you will have specified offsets from the center that represent specific binary codes.

Edit: as others have said, the tuning and demodulating are 2 different steps. Step 1 tune, When you tune you take the signal centered at the carrier, what the dial on your radio says, and recenter it at 0. Step 1 is the same for pretty much everything RF. The output is "base-band". You aren't going in and out of tune because for each center frequency, there will be an agreed variance (band width) allowed for the channel. The tuner captures this entire range and this is what is then demodulated in step 2.