[Discuss-gnuradio] Please help me understand wave.jpg [attached] representing the plot of the usrp_rx_cfile.py output

[Bishal Thapa]

Dear all,
  Please help me understand this output from usrp_rx_cfile.py. I have
attached the plot as the jpeg at the end:

1. I send a file with 1500 bytes of spaces (Space = 0x20 = 0010 0000 in
binary)
2. I use usrp_rx_cfile.py to capture the samples, and focus in on roughly
24600 samples (because 1500 bdpsk modulated bytes = 1500*8*2 + preamble +
CRC..)
3. multiplied by 2 because its 2 samples per symbol (one bit per symbol).
Therefore, I ignore every other sample. So down to 12300 samples roughly.
4. I turned off whitening and dewhitening. Hence, I should now see dbpsk
samples that represent 0010 0000 0010 0000.....
5. I do see the pattern when I look at the angle formed by those complex
symbols in MATLAB [using  plot(angle(read_complex_binary('s.dat')))]
6. But I also see some kind of unexplainable shifting once I take the
absolute value of the angles of the complex symbols [shown in the jpg].

Can somebody please tell me if there is some kind of shifting implemented in
the dbpsk modulation which causes the plot of the angle of these complex
samples
captured by usrp_rx_cfile.py to look like this. Please note that I turn off
whitening/dewhitening so the pattern do resemble 0010 0000 0010 0000
somewhat.

-Thank you for your time,
-B.

<<attachment: wave.jpg>>

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