[Discuss-gnuradio] Quadrature demodulator hardware - A further update

[Ian Wraith]

Hello
     Just a quick update to let people who are interested in this know
about my progress working on PI/4 DQPSK demodulation. With the help
and advice of another list member I was making reasonable progress. I
was providing .CSV files with I & Q channel data and he was using them
with Matlab to look at different methods of symbol timing and other code
issues. Using Matlab he searched for frequency correction bursts
which have know sequences of phase shifts and compared them to the phase
shifts seen in my data. This line of enquiry proved that my receiver
appears to have a slight frequency offset due to the differences in the
observed phase changes. In addition the poor layout of my prototype
quadrature demodulator (there is a photo of it in all its horror on the
Wiki) was introducing noise which wasn't really a suprise.

 So I have decided to neatly box it up in a nice metal enclosure I bought
at a recent rally and to put the oscillator circuit in another metal
box inside that one. I am also designing a new crystal oscillator circuit
to improve on the stability and noise levels of the old one. Unfortunetly
due to some broken parts and the fact that it is my busy time at work
mean I haven't made as much progress as I would like to have.

 Anyway once I have all that sorted out I will be starting work on the
software side of things once again.

Regards

Ian