Hello!
I'm trying to build QPSK based system on GNURadio.
I'm
using two USRP B205-mini boards as transmitter and receiver, also I got
B210 board that I run gqrx on to watch what is really going on.
I
noticed a strange behaviour on my tests, so I began to investigate it
and ended to a very simple graph, that is in attachment. On a
frequencies that are multiple of 10Mhz, like 1020Mhz all works like
expected and sonogram looks good. If I tune to any other frequency, even
1Hz more or less, the sonogram is full of pulsations and frequency of
that pulsation is depends of exact tune frequency. I attached some
screenshots of that pulsations.
On receiving part that pulsations cause many errors while decoding.
I got another board, LimeSDR-Mini, and no such behaviour observed while running graph on it.
I wonder what is going on, and how can I fix this problem.
Thank you.
pulse1.jpeg
pulse.grc
pulse2.jpeg
good.jpeg