[USRP-users] E310 Tx Rx Loopback using GNU Radio

Marcus Müller marcus.mueller at ettus.com
Mon Mar 14 13:30:48 EDT 2016

Hi Bhushan,

On 03/14/2016 01:48 PM, BHUSHAN PAWAR wrote:
>     If not, decrease (in case of clipping) or increase (in case of
>     amplitudes being too small) the gain, play with the RF frequency etc.
>     I'd say, a good setting would be if you feed in a tone, and the
>     digital amplitude of that would roughly be 0.4.
> As you have mentioned, I connected the blocks in GNU radio (Fin=435M,
> samp_rate=40k, BW=6M, gain= 60)  and analysed the file using
> gr_plot_psd_c. The results look just fine.
>     Next, instead of feeding a live signal into the USRP sink, start
>     e.g. with a baseband tone, generated by a signal source:
>         signal source(fsample=320e3, freq=16e3, ampl=0.4) -> USRP sink
>     You should be able to see that on your external measurment device.
>     If not, increase gain, etc.
> Now for the USRP sink, I connected, signal source(fsample=320e3,
> freq=16e3, ampl=0.4) -> USRP sink (ch0, ch1, centre freq=16e3,
> BW=320e3, gain=60).
No, that's not a possible parametrization of the USRP sink. Center freq
= 16kHz is impossible. The console output should clearly state that!
Try center frequency=435e6.
Center frequency is the frequency of the oscillator that will be used to
mix up the baseband signal.
Sampling rate should be the same as used with the signal source

Best regards,
> I can observe a signal on the oscilloscope but signal looks bit
> distorted and freq on the signal is 50M. I tried changing the
> parameters of signal source and USRP sink but there is hardly any
> difference in the output.
>     Now, assuming this leads to some settings that make your RX and TX
>     work on their own, using these settings in your flow graph should
>     work.
>     By the way, it's really much more comfortable to install GNU Radio
>     on your PC, too, and use the GNU Radio Companion on your PC to do
>     the flow graph design, and then copy the resulting Python progran
>     over to the E310 than to do X forwarding just to see the GNU Radio
>     companion's GUI on your PC. I can understand you're hesitant to go
>     through the installation of GNU Radio and its dependencies, but
>     luckily, there's the GNU Radio live DVD[3] which you can download,
>     burn to a DVD / write to a USB stick and boot from, giving you an
>     instantly usable GNU Radio installation on your PC, without
>     modifying anything on the PC.
> Thanks for the suggestion and all the help !!!
>     Best regards,
>     Marcus
>     [1]
>     https://gnuradio.org/redmine/projects/gnuradio/wiki/FAQ#What-is-the-file-format-of-a-file_sink-How-can-I-read-files-produced-by-a-file-sink
>     ; the octave scripts work with Matlab, too.
>     [2]
>     https://github.com/gnuradio/gnuradio/blob/master/gr-utils/octave/read_complex_binary.m
>     [3]
>     https://gnuradio.org/redmine/projects/gnuradio/wiki/GNURadioLiveDVD
>     ¹ here's a quick and dirty python analysis script I just came up
>     with; haven't tried it myself, but I don't think I made too many
>     mistakes:
>     import numpy
>     samples = numpy.fromfile("/path/to/file", dtype=numpy.complex64)
>     digital_power_of_samples = numpy.abs(samples)**2
>     mean_power = digital_power_of_samples.mean()
>     max_power = max(digital_power_of_samples)
>     print "mean power: {:f} (should be >0.05 and <0.7), max_power: {:f} (should be >0.3, <1, respectively)".format(mean_power, max_power)
>     print "variance(I): {:f}, variance(Q): {:f} (I should roughly equal Q variance, equal mean power/2)".format(numpy.var(samples.real), numpy.var(samples.imag))
>     PS: It's normal to just reply to the mailing list and not to you
>     individually if you write a mail to that list; since you're on
>     that list, you'd get that mail, anyways, and having the same mail
>     twice doesn't really help.
>     You're using gmail, so "starring" the conversation on the mailing
>     list should lead to replies on the mailing list being highlighted
>     in your inbox.

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