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[Discuss-gnuradio] Problem with sinc pulse transmission using RFX2400

From: S. Faisal A. Shah
Subject: [Discuss-gnuradio] Problem with sinc pulse transmission using RFX2400
Date: Wed, 29 Aug 2007 18:13:03 -0500


I am using a USRP with RFX2400 to transmit a sinc pulse using
usrp_siggen.py routine and my own sinc pulse generator that is a
modified version of gr_sig_source_c.cc. I am using a separate USRP
with RFX2400 to receive the pulse using usrp_rx_cfile.py. The
transmitter and receiver are one meter apart.

First, I tried to put the sinc pulse on the "I" branch (real) and
zeros on the "Q" branch. But the amplitude of the received pulse train
is time varying. In fact, the received pulse train seems to be
amplitude modulated by a low frequency signal (in KHz). Second I tried
to put the same sinc pulse on both I and Q and had the same problem.
For curiosity, I repeated the experiment by putting few cycles of sine
wave on both I and Q and encountered the same problem of amplitude
variation. Finally, I tried using a truncated sine wave on I and
cosine on Q and it works perfectly fine. I am having difficulty in
understanding the problem. Does this mean that I can only put sine and
cosine on I and Q, respectively? Is it possible to transmit only
single component not quadrature using RFX 2400? I am thinking to set
MUX to disable the Q branch at the transmitter and receiver. Any help
will be highly appreciated.

Thanks in advance,


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