On Wed, Dec 14, 2011 at 7:24 PM, Marcus D. Leech <[email protected]> wrote:
> Hi there, >> >> I made some decent progress but refining the parameters for the >> benchmark_tx.py and benchmark_rx.py without no errors. However, I can only >> transmit but I could not receive anything at the receiver side. Could >> somebody suggest what might be the problem? I tried to work it but still >> could not find answer on why I did not received anything. >> >> Used code: >> >> ./benchmark_tx.py -f 400M -r 250k -S 4 >> >> and >> >> ./benchmark_rx.py -f 400M -r 250k -S 4 >> >> OS: Ubuntu 11.10 (which I read in blog said that it has some problem with >> gnuradio) >> Gnuradio: 3.5.0 rc 0 (which I git from master branch) >> Hardware: USRP1(transmitter), USRP N210(receiver) >> Machine: Lenovo T510 (transmitter), Dell Desktop >> >> Regards, >> Muhammad >> >> A common reason for this type of problem is frequency-offset between RX > and TX. On the RX side, use uhd_fft.py to observe the spectrum > and see where the receiver thinks the peak of the spectrum is. Then > adjust your '-f' accordingly on a subsequent run of benchmark_rx.py. > > Crystal oscillators aren't perfect. Even an error of a few 10s of PPM can > add up to several Khz at center frequencies in the hundreds of > MHz. Unless the receive flow-graph has a way of correcting gross > frequency error, you will have to do that manually. > > This is such a common problem that I'm surprised you haven't covered it in > your coursework yet. Real radios (and radio channels) have > impairments that often aren't adequately modelled by simulations. > > > -- > Marcus Leech > Principal Investigator > Shirleys Bay Radio Astronomy Consortium > http://www.sbrac.org > Can someone put this in the FAQ page on gnuradio.org? It probably deserves a more detailed explanation than a FAQ-level answer, but it'd be a start. Tom
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