On Wed, Dec 14, 2011 at 7:24 PM, Marcus D. Leech
<address@hidden> 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.
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