Re: [Discuss-gnuradio] Re: A little DQPSK demodulation progress and a question

[Matthew Ettus]

> http://borg.shef.ac.uk/~ianw/dqpsk_const.html

> That said I am not sure if
> I should be worried by what I am seeing.


I wouldn't be worried.  What you are seeing is that you don't have frequency or
time sync.  It looks like you might even have some DC-offset and some IQ
amplitude imbalance.  You also have noise, and probably some fading too.  This
sort of thing is always easier when you have a very clean signal to work with.

The first thing to do is get frequency sync.  This is not as easy as it was with
ATSC or the WWVB signal, since there is no carrier component to this signal. 
You are probably best off using a Costas loop, or squaring the signal twice to
get a 4x carrier frequency.

Matt