Re: [Discuss-gnuradio] Decoding 2FSK Compensating for carrier jitter/skewing (CFO)

[Andy Walls]

> Date: Fri, 7 Jul 2017 19:50:55 +0300
> From: HLL

> Hi all,
> 
> I'm relatively new to DSP and gnuradio but I tried tons of stuff and
> I couldn't decode a fairly simple FSK data.
> baudrate seems around 600-700 bps and fsk deviation is less then 3k.


Hmmm.  I took a look at your signal and tried building a coherent 2-FSK 
demodulator.  Under the assumption that it was straight 2-FSK, the
signaling tones looked to be at +/- 1200 Hz when properly centered. The
fastest bit rate appeared to be 1880 bits/sec.

But in reality that doesn't work.  I could never get good symbol timing
recovery as the "FSK" signal appeared to have two different baud rates.

After some reflection, the signal you have appears to actually be AFSK
inside of FM.  Zoom out a little on the output of the quad demod, and
your eye can see the two tones.  The two tones appear to be at 350 Hz
and 940 Hz.  The tones are unusual in that they are square wave tones
vs. sine wave.

I haven't worked you the baud rate yet.  I'll hack away at it more
tomorrow. 

Regards,
Andy

> 
> Thanks for the help
> HLL.