[USRP-users] UHD core and sync example distortion

Marcus D. Leech mleech at ripnet.com
Mon Mar 14 20:10:15 EDT 2016

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
> 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
> _______________________________________________
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> USRP-users at lists.ettus.com
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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?

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