Re: [Discuss-gnuradio] QPSK phase noise

[Eric Blossom]

On Tue, Apr 07, 2009 at 11:07:54AM -0700, Paco Garcia wrote:
> 
> 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.

Are you getting overruns ("uOuO") on the rx side?
If so, try running at a lower data rate, say 500k.

Eric