[Discuss-gnuradio] QPSK phase noise

[Paco Garcia]

Dear All,

I am trying to demod a qpsk from another USRP but with the setup below I get
a really noisy constellation:

http://img231.imageshack.us/img231/2465/screenshotysh.png

The 2 USRPs are connected via a SMA cable with 40 db attenuators and DC
blocker.
I have also played with the costas alpha, samples per symbol, gain mu,
frequency fine tunning and this is the best result I can get.

./benchmark_tx.py -m dqpsk -f 1.25G -m dqpsk --tx-amplitude=10000 -r 1M -M
99999999 --excess-bw=0.35
./benchmark_rx.py -r 1M -m dqpsk --log --costas-alpha=0.05 -S 4 --verbose -r
1M --gain-mu=0.01 --excess-bw=0.35 -f 1.25G

Thanks for your help.


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