some small things: * I am pretty sure you cables are not phase matched (costs about 5K for a 26” matched pair), so you will get some difference there. Not sure how to quantify. * Splitters have a phase mismatch, I think its called phase unbalance, proportional to cost :), but can be multiple degrees. * even between 2 channels on the same device, there will be some phase noise
Still seems far away from 18 degrees, so cant help more than above... > On May 8, 2018 at 11:17 AM "shachar J. brown via USRP-users" > <usrp-users@lists.ettus.com> wrote: > > > Hi Jeff, > > Thanks for your response, but you understood me completely wrong. > > Of course I have set the RF freq in the source block. Furthermore, I have > fully analized the signal from both chanels, and it appears crystal clear in > all the sinks throughout the flow graph (e.g., a pure max at the correct bin > after the FFT in the vector sink, and a beautiful phase gain in the time sink > after the phase extraction). > > My problem isn't receiving the signal or analizing it. My problem is that > the phase difference between the two channels does not match the theory. The > wire to one channel is longer than the other by at least 1/6 of a wavelength, > whilst the phase diff was only 1/10 of 2*pi. > > Am I understood? > > Does anyone have a clue what's going wrong? > > Thanks again, > > Steve > > > > On 05/07/2018 11:11 AM, shachar J. brown via USRP-users wrote: > > Hi All, > > > > I am trying to measure the phase difference of a received signal > between > > the two RX ports of the B210. (In the grc I simply ran each of the two > > received signals through an FFT, took the bin with highest amplitude > and > > extracted it's phase, and finaly - subtracted the two). > > > > I experimented with a single signal source generator split in two. I > > first connected both RX ports with matching wires and received zero > > phase difference as expected. > > > > Though when I added a wire of some length to one of the ports, the > > received phase difference was NOT as expected by theory. > > > > (In short, I sent 100[Mhz] pure sine wave, thus wavelength of 3[m] or > > shorter, the extra wire was 0.508[cm] long, thus I would expect a phase > > diff of about 60 deg or more. Frankly I received a phase diff of about > > 18 deg). > > > > What am I doing wrong? > > > > I thought maybe the phase calculation of gnuradio is done on the > > baseband frequency and not on the RF, and therefore the phase diff > would > > be different. Is this my problem? (e.g. if the baseband is only > 30[Mhz], > > then expected phase diff would be 18 deg). If that is the case - how > can > > I know which baseband frequency the AD9361 has chosen? > > GNU Radio works with signals at baseband. It sounds like you might not > have set a RF frequency in the USRP source block. The default is 0, and > I'm not sure what the B210 would tune to in that case. > > I don't know whether this experiment actually works, but to do it you > would tune to 99M, set the sample rate to 2M, and see what happens. The > peak should be right in the middle. > > Also, make sure your signal generator is sending out a very low signal - > try something like -40dBm. Max is higher, but there's no need. > > > > > Thank you all for your time, > > Steve > > > > > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >
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