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

Jim Hunziker jhunziker at bcisensors.com
Wed Oct 22 16:42:49 EDT 2014


It looks like some of my problem was plotting abs(sig_c) rather than
real(sig_c), but the signal still doesn't look great.


-- 
Jim Hunziker
BCI Systems and Software Engineering
(973) 348-9299
jhunziker at bcisensors.com

On Wed, Oct 22, 2014 at 12:15 PM, Jim Hunziker <jhunziker at bcisensors.com>
wrote:

> 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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