[USRP-users] UHD core and sync example distortion

Steven Knudsen ee.knud at gmail.com
Tue Mar 15 08:57:28 EDT 2016


Thanks, Marcus.

Yes, I had gone back to basics, pure tone, real sinusoid (split tone), and such. I can confirm that the carrier leakage specs for the AD9364 are better than the datesheet :-)

I worked through some of the math last night and am thinking now that I was being naive (forgetful of something I should know...) and not accounting for in-band noise. That makes sense since it seems clear from the image I attached (to the previous email) that sync was working fine; the two constellation points are 180 degrees on the real axis and don’t waver much above or below. Going back to the QPSK experiment I was able to get a much tighter constellation by simply playing with sampling and symbol rates.

This implies that a LP decimating filter might be a good thing to include in my receiver ;-)

So, I think the ball is back in my court, and I apologize for wasting your and others time. I should probably write up a little blog entry or something on sampling and in-band noise… though I bet that’s already out there.

Thanks for responding!

steven

PS, for anyone interested, I’ve attached two images from a spectrum analyzer generated using the tx_waveforms example application and SINE waveform @8192Hz. One is with 50 dB Tx gain and the other with 89.5 dB gain. Marker 2 is the leakage level. There is a 30 dB attenuator in the line.

Steven Knudsen, Ph.D., P.Eng.
www. techconficio.ca
www.linkedin.com/in/knudstevenknudsen

Der entscheidende Augenblick der menschlichen Entwicklung ist immerwährend. Darum sind die revolutionären geistigen Bewegungen, welche alles Frühere für nichtig erklären, im Recht, denn es ist noch nichts geschehen. - Franz Kafka


> On Mar 14, 2016, at 18:10, Marcus D. Leech via USRP-users <usrp-users at lists.ettus.com> wrote:
> 
> On 03/14/2016 08:00 PM, Steven Knudsen via USRP-users wrote:
>> Hi All,
>> 
>> I have tried to get the corr and sync example from gr-digital to work with the B200mini. Obviously, I changed the input to the UHD sink so that the magnitude is < 0.7 (set to 0.5 or 0.3) and set the Tx and Rx slider max values to match the B200mini gains.
>> 
>> As can be seen in the attached image, it appears that there is some amplitude distortion or fluctuation. I would expect the constellation to be more symmetric and certainly tighter.
>> 
>> It doesn’t seem to matter how I sync the UHD Sink/Source blocks (1 PPS, PC, not at all).
>> 
>> I have tried s simpler QPSK streaming example based on the Polyphase Clock Sync example of the online tutorial, and see similar behaviour. 
>> 
>> I have tried all kinds of settings for Tx and Rx gain. Measured input power to the B200mini is -80 dBm.
>> 
>> Does anyone have experience with the B200mini and this or similar examples? If so, how do you set things up to get clean results?
>> 
>> Thanks very much for your time and consideration,
>> 
>> steven
>> 
>> <Mail Attachment.jpeg>
>> Steven Knudsen, Ph.D., P.Eng.
>> www. techconficio.ca <http://techconficio.ca/>
>> www.linkedin.com/in/knudstevenknudsen <http://www.linkedin.com/in/knudstevenknudsen>
>> 
>> All the wires are cut, my friends
>> Live beyond the severed ends.  Louis MacNeice
>> 
>> 
>> 
>> _______________________________________________
>> USRP-users mailing list
>> USRP-users at lists.ettus.com <mailto:USRP-users at lists.ettus.com>
>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com <http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com>
> With this type of debugging it's often useful to go back to something very, very simple, and see what the results are.  Presumably, you're
>   looping back between TX and RX with a cable?  How much attenuation in that cable?
> 
> If you send a pure tone (or pair of tones, even) what do they look like on the RX side in both the frequency and time domain?
> 
> 
> _______________________________________________
> USRP-users mailing list
> USRP-users at lists.ettus.com
> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/attachments/20160315/1ed876b2/attachment-0002.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Tx SINE 50dBgain.png
Type: image/png
Size: 60716 bytes
Desc: not available
URL: <http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/attachments/20160315/1ed876b2/attachment.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Tx SINE 89.5dBgain.png
Type: image/png
Size: 62280 bytes
Desc: not available
URL: <http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/attachments/20160315/1ed876b2/attachment-0001.png>


More information about the USRP-users mailing list