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[Discuss-gnuradio] Recording I-Q stream with uhd_rx_cfile

From: Nazmul Islam
Subject: [Discuss-gnuradio] Recording I-Q stream with uhd_rx_cfile
Date: Thu, 24 May 2012 19:07:56 -0400


I want to transmit a continuous stream of 1's or 0's (with bpsk modulation) and record the received I-Q stream. I am trying to use the 'digital_bert_tx.py' code for transmission and the uhd_rx_cfile code (gr-uhd/apps) for reception. Thereafter, I use the read_complex_binary code to read the data in Matlab.

Surprisingly, I am receiving similar type of I-Q stream (around 0.3 + j 0.3) for both 1 and 0 transmission. I am using the following commands:

self._bits = gr.vector_source_b([1,], True)                       (I either transmit infinite 1 or infinit 0's. When I transmit infinite 0's, I replace '1' by '0' in the command)

./digital_bert_naz_tx.py -r 5M -m bpsk -f 450M --gain 0.1 --non-differential    (I am using non-differential since I want to see the different amplitude levels for '1's or 0's)

./uhd_rx_cfile -N 1000 -f 450M --samp-rate 5M file.dat   (Since I am using bpsk, sample-rate should be equal to bit rate, I assume)

Ideally, the I-Q stream of bpsk should show 180 degree phase shift for 1 and 0 transmission. I am getting the same value for both transmission. Can anyone suggest where I am making mistakes?



Muhammad Nazmul Islam

Graduate Student
Electrical & Computer Engineering
Wireless Information & Networking Laboratory
Rutgers, USA.

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