Hi all, I use two USRP B200 with wired connection, one with QPSK modulator, and the other with the general_demodulator structure: (USPR Source --> AGC2 --> FLL Band-Edge --> Polyphase Clock Sync and so on...) But neither I use them with External 10MHz reference on both board or not, or just in simulation (the mod and demod together with channel models) the FLL Band-Edge not work for me. In real connection it can't sync the frequency porperly for the Polyphase Clock Sync (PhCS) block. I know it would never be a perfect sync, but I think it should sync the frequency within a tolerance for the PhCS block, expecially with the external reference signal. I've tried almost every number for the loop bandwith parameter, but the best solution is a noisy circular constellation. Here is the grc files for my setup: https://gitlab.com/tomiszili/my-demod-sync.git What I'm leaving out for a better sync performance? What GRC block should I use for a proper frequency sync? Any other suggestion? Best regards Tamas

It's possible that the FLL is throwing off the clock sync. One issue with the FLL is that it tracks too fast, and thus will continuously apply small frequency offset corrections based on its noisy estimate. I would suggest also asking this on discuss-gnuradio (although you're welcome to post this question here too!), where there's probably more people who can chime in with this discussion. Cheers, Martin On 12/01/2016 01:12 AM, Tamás Szili via USRP-users wrote: > Hi all, > > I use two USRP B200 with wired connection, one with QPSK modulator, and > the other with the general_demodulator structure: (USPR Source --> AGC2 > --> FLL Band-Edge --> Polyphase Clock Sync and so on...) > > But neither I use them with External 10MHz reference on both board or > not, or just in simulation (the mod and demod together with channel > models) the FLL Band-Edge not work for me. In real connection it can't > sync the frequency porperly for the Polyphase Clock Sync (PhCS) block. I > know it would never be a perfect sync, but I think it should sync the > frequency within a tolerance for the PhCS block, expecially with the > external reference signal. I've tried almost every number for the loop > bandwith parameter, but the best solution is a noisy circular constellation. > > Here is the grc files for my setup: > https://gitlab.com/tomiszili/my-demod-sync.git > > What I'm leaving out for a better sync performance? What GRC block > should I use for a proper frequency sync? Any other suggestion? > > > Best regards > Tamas > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >