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MRAM mentioned checking the stereo subcarrier, and I want to explore that idea further.
The FM subcarrier, centered on 38kHz, is the carrier for the L-minus-R signal, which gets decoded at the receiver where, mixed with the L+R Mono signal, gives a proper left and right set of channels.
The 19kHz signal tells the receiver to turn on the stereo light, but this “pilot tone” is not a stereo carrier.
Here is a useful description of how it all works
