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

Michael West michael.west at ettus.com
Wed Oct 29 18:32:33 EDT 2014


Hi Jim,

I set up an X310 and CBX-120 with a loopback cable between TX/RX and RX2
and ran the same command as in your test.log file (with a reduction of the
sample rate to 10 Msps and not using the CAL antenna).  I did add the
argument "--type float" to get fc32 samples in the file so I could use my
existing GRC flowgraph to plot the data.  I saw no issues in the resulting
data (see the attached screenshot of the FFT and scope plots).  I then set
up a quick GRC flowgraph with the same settings and FFT and Scope sinks
connected to the USRP Source.  I saw no issues at all (see the attached
screenshot).  The fact that you see no issues when using external
instruments and the same command works just fine for me suggests that there
is some problem with how the data is being processed to generated the
graphs.  You could try switching to the float type and see if your results
get any better.

By the way, I also did a run with the RX antenna set to CAL and I noticed
that the signal strength was about 30-35 dB lower (as expected).

Regards,
Michael

On Wed, Oct 29, 2014 at 12:29 PM, Jim Hunziker <jhunziker at bcisensors.com>
wrote:

> OK, as Frank said in a separate email, the cal patch didn't seem to fix
> our problems. The only thing we're using to control the X310 (and CBX-120)
> is txrx_loopback_to_file.
>
> Attached is a zip file with a log of what we're doing and some images to
> go along with it. Our X310 isn't hooked up to anything, and we're using CAL
> as the receive antenna. (We've tried this same test with a loopback cable
> and RX2, but it doesn't make a difference.)
>
> The fft.png image is an FFT of the received data, zoomed to baseband and
> the 1 MHz signal that was up- and down-converted to 5.6 GHz. You can see
> the 1 MHz signal at the correct frequency. The other images are showing the
> quality (or lack thereof) of the received signal. Not long after the
> capture starts, the 1 MHz signal is no longer detectable.
>
> In the test.log file, you can see how we're running txrx_loopback_to_file
> and what gets spit out as it runs. You can also see the commands that I'm
> using (in Python, with NumPy, though the commands are nearly the same as
> their MATLAB equivalents) to generate the images.
>
> The problem does not seem to occur (or at least not as badly) when we
> capture the transmitted data with external test equipment. It also doesn't
> seem to occur when we capture a signal from a signal generator with the
> X310. All tests, even these last two, were done using
> txrx_loopback_to_file. So our best guess is that something weird is
> happening inside the X310 when it is being used to do a full duplex TX/RX.
>
> If you like, I can also provide usrp_samples.dat.
>
> --
> Jim Hunziker
> BCI Systems and Software Engineering
> jhunziker at bcisensors.com
>
> On Mon, Oct 27, 2014 at 4:05 PM, Jim Hunziker <jhunziker at bcisensors.com>
> wrote:
>
>> I found the problem. I had to run dos2unix on the patch first. I'll get
>> back to you on how it affects our tests. Thanks!
>>
>>
>> --
>> Jim Hunziker
>> BCI Systems and Software Engineering
>> jhunziker at bcisensors.com
>>
>> On Mon, Oct 27, 2014 at 1:32 PM, Michael West <michael.west at ettus.com>
>> wrote:
>>
>>> The patch should work for any version of UHD from 3.7.0 forward.
>>>
>>> Michael
>>>
>>> On Mon, Oct 27, 2014 at 7:48 AM, Jim Hunziker <jhunziker at bcisensors.com>
>>> wrote:
>>>
>>>> Thanks. It looks like this patch isn't against 3.7.3. We're not running
>>>> against the master branch right now. Is this patch intended for 3.8-rc?
>>>>
>>>>
>>>> --
>>>> Jim Hunziker
>>>> BCI Systems and Software Engineering
>>>> jhunziker at bcisensors.com
>>>>
>>>> On Fri, Oct 24, 2014 at 5:55 PM, Michael West <michael.west at ettus.com>
>>>> wrote:
>>>>
>>>>> Hi Jim,
>>>>>
>>>>> An experimental UHD patch was sent to your colleague to address the
>>>>> calibration issue.  Please let me know if you need the patch sent to you
>>>>> directly and I will get it to you.
>>>>>
>>>>> Best regards,
>>>>> Michael
>>>>>
>>>>> On Thu, Oct 23, 2014 at 10:40 AM, Jim Hunziker via USRP-users <
>>>>> usrp-users at lists.ettus.com> wrote:
>>>>>
>>>>>> Marcus Leech responded to me off-list that I was using gain settings
>>>>>> that were too low. Setting them to 10 greatly improved my signal, though
>>>>>> there's still a carrier component that's bigger than my signal and not
>>>>>> getting removed. A colleague tells me he's working with Ettus regarding
>>>>>> this problem.
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Jim Hunziker
>>>>>> BCI Systems and Software Engineering
>>>>>> jhunziker at bcisensors.com
>>>>>>
>>>>>> On Wed, Oct 22, 2014 at 4:42 PM, Jim Hunziker <
>>>>>> jhunziker at bcisensors.com> wrote:
>>>>>>
>>>>>>> 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
>>>>>>> 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
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> USRP-users mailing list
>>>>>> USRP-users at lists.ettus.com
>>>>>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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