Oh! If that is the case, yes, please do make an example FG, and if you find the time, also open an issue on https://github.com/gnuradio/gnuradio/issues .
Thanks! Marcus On 07/07/2017 07:19 PM, Anon Lister via USRP-users wrote: > FYI I've noticed a very similar issue, isolated it to non usrp > gnuradio blocks in tx chain. Specifically the constellation or *psk > modulator blocks. Certain combos produced garbage IQ data(visible as > several spikes in PSD display) at regular intervals (seemingly related > to sample rate), this is visible even with a very simple flowgraph, > dumping data to a file, no USRP involved. I actually changed the > underlying data I was modulating and the bad data appeared at the same > position in time no matter how many times I ran the flowgraph. I did > try moving the symbols closer away from unity, so used something like > (-.707, .707) but that didn't change anything. > Still haven't completely eliminated user error, so I was going to try > to make an example flowgraph later today and submit to discuss-gnuradio. > > On Jul 6, 2017 9:38 PM, "Michael Carosino via USRP-users" > <usrp-users@lists.ettus.com <mailto:usrp-users@lists.ettus.com>> wrote: > > A quick update to this question with more info. I did some further > analysis by capturing the received I/Q data from the USRP Source > block when transmitting the BPSK that works without errors > (symbols are 0.707+0.707j, -0.707-0.707j) and also when using the > BPSK that gives errors (symbols are +1/-1). You can see in the > attached image there is quite a bit of small magnitude anomalies > for the second image (also errors are probably occurring a bit > more frequently than I had previously estimated). > > To me this points to the issue being either something to do with > the USRP or possibly with the TX chain blocks. > > On Thu, Jul 6, 2017 at 4:37 PM, Michael Carosino > <m.caros...@gmail.com <mailto:m.caros...@gmail.com>> wrote: > > Hi all, > > running Gnuradio 3.7.10.2 and UHD 4.0.0 rfnoc-devel latest > commit (tried earlier versions too). I've got a simple tx/rx > flowgraph going on. The simple description is: > > Random input data -> Pack 1 Bit->Chunks to > Symbols->Interpolating FIR Filter->USRP Sink > > USRP Source-> Polyphase Clock Sync -> Costas Loop-> > Constellation Receiver->Unpack 1 Bit > > > I'm transmitting on RF-B TX/RX and receiving on RF-B RX. The > system works almost perfectly, except that there are single > bit errors occurring (not many, maybe every couple of seconds > at 500k samp rate). > > Now here's the real strange thing, these errors are ONLY > present if running real BPSK (-1,+1), imaginary BPSK (+j,-j), > or rotated QPSK/QAM (+1j,-1j,+1,-1) > > If I use a BPSK having symbols with real and complex parts > like (-.707-.707j, .707+.707j) or QPSK (+/- .707+/- .707j) the > errors are NOT present. > > A couple more notes: > Happens if using different x310s or the same for tx/rx. > Happens even if I try to add a small complex value before > sending data to the USRP. > Error always happens as a single bit error (not bursty). > > Attached are the constellation plots out of the polyphase > clock sync (PFB) and the costas loop. My guess is the issue is > either at the USRP or the Polyphase Clock Sync block. > > Anyone seen something like this before? I'll probably start > diving in the polyphase clock sync code to figure what's going on. > > Thanks, > Mike > > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com <mailto:USRP-users@lists.ettus.com> > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > <http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com> > > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
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