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259 points zdw | 1 comments | 13 Oct 24 22:32 UTC | HN request time: 0.204s | source

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massysett ◴[14 Oct 24 00:39 UTC] No.41833059[source]▶

What I’ve never understood is how the FM receiver can lock on to the signal if its frequency is always changing. Doesn’t the receiver need to lock on to something? If the answer is “it locks on to the amplitude, which doesn’t change,” well AM is bad because the amplitude is subject to interference, so wouldn’t FM have the same problem?

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1. jedimastert ◴[14 Oct 24 01:12 UTC] No.41833231[source]▶

>>41833059 #

I'm actually studying for my general ham radio license right now! Most FM receivers use something called a "mixer" to modulate the frequency to a known constant, then they use a circuit called a "discriminator" or "quadrature", both of which are "detectors".

Typically they're not measuring the frequency or phase itself, but rather the change in frequency or phase.

Edit: I should note that's only for analog circuits. DSP is also common.

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Why does FM sound better than AM?