[Discuss-gnuradio] PLL simulation

[Leo Silva Garcia de Britto]

Hello,

I'm a student trying to simulate a pll for a computer based radio, similar 
to the one you are trying to deliver and i am facing a few problems to 
understand your code.

I need to simulate a phase locked loop to sync a 6.25 KHz carrier sampled
at 200 KHz. It is a sincronization system using a costas loop: a 
m-power(4) followed by a band pass(25 KHz) followed by the pll to get a 
lock in the carrier frequency? Is this clear? If not i can supply a figure
that would clarify things better...

So i started reading gnuradio's code to find some ideas on the pll design, 
but it seems there's nothing similar in it... you have a GrCostasLoop and 
a gr_nco files that seem to just demodulate a quadrature modulated 
signal(like if it was supposed to be used in a soundcard stereo output or 
the like, please correct me if i'm wrong).

The Costas loop implemented tries to get a phase lock from the two 
channels that are filtered apart after beeing mixed with a sine and a 
cosine wave generated by the nco controlled by a reference derived from 
the phase diference between both demodulated channels(is it correct?).

First of all i can't really understand how this scheme can possibly 
work(though it probably do otherwise it wouldn't be there up to now). And 
it seems to me you're considering your symbols to be sync'ed. The problem 
for me is that i can't separate my input stream in two channels just by 
splitting the incomming data stream because data is modulated in each of 
the basis functions beeing used(like a*sin(phi)+b*cos(phi).

And how could i get a reference out of this GrCostasLoop to perform symbol 
timming and carrier frequency recovery? So i could try diferent modulation 
constelations.

Thanks for any help,
Leo