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
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