Hi Kevin, I got inverted spectrum (that means sign of I or Q is changed) when I only set the frequency with use of timed commands. I described the ranges in the original post. We did measurements in 100-500MHz band. You can see phase difference between two TwinRXes here: https://imgur.com/4C09MSf
Slight change of frequency didin't seem to help. I.e. in whole 128-172MHz the phase difference was continuous, then there was ~90 degree discontinuity at 172MHz, then at 245MHz there was another with opposite sign and so on. I don't know what might be causing this. After looking at the diagram of TwinRX there doesn't seem to be any circuit that might do such changes of the LO phase. Maybe something in the FPGA. I'm puzzled... Best Regards, Piotr Krysik W dniu 04.04.2019 o 23:00, Rigney, Kevin E via USRP-users pisze: > Pitor: > > We've seen a similar issue and have worked around it by just using a slightly > different frequency. Can you post the frequencies that you're seeing it on? I > think Ettus should be able to duplicate. I saw an issue with spectral > inversion (I think I and Q are getting swapped somewhere) at 2.8GHz but not > 2.9GHz. > > -Kevin > > On 4/4/19, 12:00 PM, "USRP-users on behalf of > usrp-users-requ...@lists.ettus.com" <usrp-users-boun...@lists.ettus.com on > behalf of usrp-users-requ...@lists.ettus.com> wrote: > > Hi, > > After disconnecting LO cables signal on the daughter-board that imports > LOs disappears. So GNU Radio correctly configures distribution of LOs. > Also the +/- 90 degree changes happen completely deterministically in > given ranges of carrier frequencies. > > So the question remains open: what is causing the issue described in the > first post of this thread? > > -- > Best Regards, > Piotr Krysik > > W dniu 03.04.2019 o?12:15, Fabian Schwartau via USRP-users pisze: > >Hi, > > > >yes, the result for multiple measurements (start ups of the system) at > >a single frequency was different by multiples of 90?. > >We did not investigated the problem any further, but I am quite sure > >that gnuradio was not synchronizing the channels using the LO-sharing, > >although it was selected. So do the test I described. If you see that > >he is not using the LO-sharing, you know where to look further. > >Keep in mind that it is not necessary to use LO-sharing to get a well > >defined phase relation between the channels. Depending on your > >frequency and bandwidth settings, it is possible to also achive this, > >as all LOs are driven from a common 200 MHz reference clock. > > > >Best regards, > >Fabian > > > >Am 03.04.2019 um 12:05 schrieb Piotr Krysik via USRP-users: > >>Hi Fabian, > >> > >>W dniu 03.04.2019 o?11:05, Fabian Schwartau via USRP-users pisze: > >>>Hi Piotr, > >>> > >>>we once had a very similar issue. But we also saw this on the same > >>>frequency when switching between frequencies. Can you try this as > >>>well? Just switch forth and back between two frequencies and just plot > >>>one of them? > >> > >>I'm not sure I understand correctly what you mean. You mean that the > >>result for a given frequency was not stable in your case across many > >>measurements? In our case this situation was repeating, but the > >>application doing the recording was restarted for each measurement. > >> > >>>As far as I remember the issue was because we were not using the > >>>LO-Sharing. We were able to get everything running by using a C++ > >>>application and not gnuradio (I can see you are using python - which > >>>is basically the same). There was a bug in gnuradio/python causing > >>>this issue. > >>>You can try to remove one of the LO-sharing cables while doing a > >>>measurement and see if the phase suddenly starts to do crazy things > >>>(the signal should also be lost). If that is not the case, you are not > >>>actually using LO-sharing. > >>> > >>Do you know what this bug was exactly? GNU Radio didn't configure > >>LO-Sharing the way it was specified? > >> > >>-- > >>Best Regards, > >>Piotr Krysik _______________________________________________ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
