[Discuss-gnuradio] fsk mod-demod

[Bob Vincent]

I've been working with fsk_tx and fsk_rx between a pair of usrp boards.
I've noticed that the fsk_tx has widely different behavior for different 
settings.
On the nominal rx board, I run the fft display, expecting to see the same 
fft as in the tx window.
What I see instead is pretty much noise.
When I run the siggen, I've got a nice strong tone at the right frequency.
On an external scope, I see the waveform mostly looking ok for the nominal 
settings (looks a lot like a sine wave, and if you open it up, looks like 
two sine waves.
I've been running with a 4e6 cordic frequency.
I'm coming to the conclusion that perhaps something is broken in the usrp 
interp filter.

Any suggestions for settings, or places to look? I'm also trying to cut 
down the data rate through the USB, and that seems to have some similar 
problems.