[Discuss-gnuradio] FSK - newbie questions

[Fergus Noble]

Hi,

I'm currently working on implementing a 2-level FSK receiver with gnu 
radio and have
got a simple demo running which uses bandpass filters to isolate the 
mark and space freqs
and finds the difference in their amplitudes.

The input to the system is currently from the sound card, from an normal 
SSB radio reciever
but we were planning to switch over to USRP style hardware in the future 
but I was just trying
to get gnu radio working with out current hardware to smooth the transition.

Ideally I would like the software to work with the new hardware with 
little modification, so although
my input now is just a float stream, I think I should be working with 
quadrature signals from the start. In
which case passing the sound card input through a Hilbert filter will 
give me a quadrature signal,
is this correct? Also do you think this is the way to go about it?

Also I have noticed in some of the MSK examples use the quadrature 
demodulator block, is this applicable
to non-continuous phase FSK and if so is it more robust than the filter 
method?

Also, the next problem is bit recovery, I don't really understand the 
correlator block, could anyone
point me towards some documentation that would be grand. Am I supposed 
to be using this or the
clock recovery block?

Sorry for the naivety of these questions, only just starting up the long 
comms learning curve.

Many Thanks,
Fergus Noble