In modulating the 4FSK using a random number (rand() % 4) I get this
spectrum:
[image: 4fsk-rand.png]
Looks good. Now if I modulate it with the vocoder bits instead:
[image: 4fsk-voice.png]
Well, isn't that special. I have no idea where those harmonics comes from,
but there is always a pip at 1400 (center frequency). Plus the garbage on
the right. Heck, there are only 4 frequencies possible in the modulator.
I guess swinging from say F1 in one instant to F4 in the next, must be a
dirty process. More than likely, it's just a well hidden bug.
It's a puzzle so far :-)
Steve
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