[USRP-users] problem with USRP example on X310 with CBX-120

Jim Hunziker jhunziker at bcisensors.com
Wed Oct 22 12:15:24 EDT 2014


Hi. I have an X310 with a CBX-120 and a GPSDO, and I'm running the
txrx_loopback_to_file example with UHD version 3.7.3 like this:

./txrx_loopback_to_file --tx-args addr=10.10.10.90 --nsamps=250000
--tx-rate 2500000 --rx-rate 2500000 --tx-freq 56000000
00 --rx-freq 5600000000 --rx-ant CAL --wave-type SINE --ref internal
--wave-freq 1000

(It makes no difference if I use the RX2 antenna and a loopback cable.)

With a sampling rate of 2.5 MHz and a sine wave of 1 KHz, I expect to see a
sinusoidal cycle every 2500 samples. I'm plotting them with GNU Octave and
the following commands:

fid = fopen("~/uhd/host/build/examples/usrp_samples.dat", "rb");
[sig, count] = fread(fid, Inf, "int16");
sig_c = sig(1:2:end) + j * sig(2:2:end);
plot(abs(sig_c));

The signal seems very noisy, and it's pretty much gone towards the end of
the capture. Am I doing something wrong?

-- 
Jim Hunziker
BCI Systems and Software Engineering
jhunziker at bcisensors.com
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