Hi Steve,
I wouldn't be too concerned, spectrums move in mysterious ways.
Couple of ideas:
1/ Try the same test on an x86
2/ Measure the BER of the transmitted signal with calibrated noise,
that's the ultimate test of any modem.
Cheers,
David
On 14/06/18 05:57, Steve wrote:
In modulating the 4FSK using a random number (rand() % 4) I get this
spectrum:
4fsk-rand.png
Looks good. Now if I modulate it with the vocoder bits instead:
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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