Hi Mathew, the random source outputs bytes with numbers 0 or 1 (NOT 2). This single bit information is "packed" into a byte that is the input to the QAM modulator. The QAM modulator internally breaks up these bytes and uses every 4 bits to signal the 16QAM constellation.
best, Achilleas On Tue, Nov 20, 2018 at 3:03 PM Matthew J. Brandsema <mjb...@arl.psu.edu> wrote: > Hello, > > When I switched AC coupling off, it just went blank. > > So instead, I saved the waveforms to a file and plotted the result in > Matlab. See attached for plots. The blue curve are the data before > modulating, and the red x's are the data after demodulating. They are > lined up! > > Thanks so much for the help in getting this working!!! I noticed the > random numbers are only 0, 1 and 2. How the heck does this work for 16 > QAM? How does it encode 3 numbers to 16 symbols? > > My next step is to transmit and receive using two Ettus radios next. I > got them to transmit and receive but I can't seem to find a delay that will > make them sync up like I did with the file you sent. > > I saved their IQ waveforms to see how out of sync they are by doing a > correlation and the correlation peak seem to be changing between data > collects. Does anyone have any idea of what might be happening? (Sorry to > add another question, I have been trying all day to get this working). > ------------------------------ > *From:* Achilleas Anastasopoulos [anas...@umich.edu] > *Sent:* Tuesday, November 20, 2018 1:25 PM > *To:* Matthew J. Brandsema; Discuss-gnuradio@gnu.org > *Subject:* Re: [Discuss-gnuradio] Packet Decoder Breaking when adding > noise > > Can you switch off the AC-coupling, and check the scope plot again. > Also, maybe useful to have markers instead of just lines. > > The two streams should be perfectly synchronized (for low noise) and as > noise gets higher > some of the demodulated bits are in error. This is perfectly OK. > > Achilleas >
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