blinry on Nostr: 6: Listen to *stereo* FM radio How stereo audio is transmitted is really interesting, ...

6: Listen to *stereo* FM radio

How stereo audio is transmitted is really interesting, because it's backwards-compatible to receivers that don't support it:

Here, you see the demodulated audio frequency spectrum. Below 19k Hz, it's just mono audio. Then, to mark a stereo station, there's a constant "pilot tone" at 19k Hz! (Outside of what most humans can hear.)

Then, if you double the frequency of the pilot tone, you can derive the sections where the left & right channel is transmitted!