So I was showing off my HackRF to my daughter, and we built an FM receiver
and listened to the music, and we also had it receive two channels at the
same time and built a fader to move between one or the other (or mix) on
the output. But the next step didn't go as planned, what I was trying to do
was pull out the sub carriers for the left and right channels. So the spec
tells me there is a subcarrier 19khz to the 'right' of the center frequency
and one to the left.
So took the output of the 100khz low pass filter coming off multiplier,
and multiplied it by 19k and -19k and took those outputs as the left and
right channels. Not what I expected. Both sides "sound" the same (I put
them through my fader into the sound sink) and even putting the subcarrier
frequency all over the map it doesn't change, so I'm clearly not doing what
I think I should be doing.