Thanks for your detailed reply. To what I have studied yet polar
discriminator will be affected more by the amplitude variations during
transmission. Currently I do not know how to cater these variations, I
reading literature on it.
Currently, I am trying to implement correlation receiver using FIR
filters. I am looking into polyphase filterbank channelizer to
correlation, but currently unable to do so because I currently do not
how to assign taps for channelizer.
practical system, if your FSK shift is sufficiently larger than your
Oversampling at baseband ? I am currently sampling at 1Msps (usrp sink
sampling rate) for a tone spacing of 125KHz. You mean after the USRP
block I should upsample again and then do the correlation? Or you mean
something else ? Please forgive me for asking too many question, I am
All in all, the question which demodulator architecture to use is an
academic/research one and not related to the implementation in GNU Radio
modulation. This is a highly interesting field and I can but encourage
you to read a lot of books  and papers on this.
Thanks for the link, nice stuff.
Assuming you don’t want phase jumps between symbols, why not just use
the VCO block to generate frequencies out of your input values?
Wow! modulation is easy using VCO. A question, why would someone want
jump between symbols?