You can test the hypothesis using a heat gun. Sent from my iPhone
> On Oct 17, 2018, at 1:13 AM, Francois Quitin <fqui...@ulb.ac.be> wrote: > > We use 30cm high quality sma cables, so I'm a bit surprised that this would > be thermal noise... > > n 17.10.2018 05:23, Marcus D. Leech wrote: >>> On 10/16/2018 04:49 PM, Francois Quitin wrote: >>> Units are radians. There is some noise because the post processing is a bit >>> crummy, but we were more concerned about the drift. >> How long is the cable that is being used to link the two X310 REF ports? >> Looks like the drift is about 0.3 radian, and it looks like a thermal >> effect to me, but that would likely not be the case for a short cable. >>> n 16.10.2018 22:46, Marcus D. Leech via USRP-users wrote: >>>>> On 10/16/2018 04:39 PM, Francois Quitin via USRP-users wrote: >>>>> Oops, I forgot to explain the figures. We're sending a pilot tone with a >>>>> different usrp, and split it over the 4 channels using a 4-port RF >>>>> SPLITTER. The graph shows the phase of the received signals as a function >>>>> of time (1 point every ten seconds) >>>>> Francois >>>> OK, but what are the phase units? Degrees? Radians? >>>>> 16.10.2018 18:13, Marcus D. Leech via USRP-users wrote: >>>>>>> On 10/16/2018 07:44 AM, Francois Quitin via USRP-users wrote: >>>>>>> Dear all, >>>>>>> We encountered a small problem when we try to build a 4-element MIMO >>>>>>> array with two X310 (equipped with UBX daughterboards). We are >>>>>>> working on UHD-3.10.3: >>>>>>> - When we use an octoclock to provide the 10 MHz >>>>>>> Ref and the PPS to both X310, the phase of each receiving front-end >>>>>>> stays nicely constant (see octoclock.png). The Ref Source and Time >>>>>>> Source are set to “external” in GNU Radio (the points represent >>>>>>> a measurement taken every ten seconds) >>>>>>> - When we use the 10 MHz Ref Out and PPS Out from >>>>>>> one X310 and feed it to the Ref In and PPS In of the other X310, we >>>>>>> observe a drift in the phases of the channels from the second X310. >>>>>>> This is shown in the graph daisyChain.png, where we take one point >>>>>>> every ten seconds. We configured GNU Radio to set the Ref Source and >>>>>>> Time source of the first USRP to “default”, the ones of the >>>>>>> second USRP to “external”. >>>>>>> This drift is something more severe, sometimes less, but it’s >>>>>>> always present. Any idea why we observe this? >>>>>>> Many thanks, >>>>>>> François >>>>>> What is the Y-axis scale on these plots? >>>>>> _______________________________________________ >>>>>> USRP-users mailing list >>>>>> USRP-users@lists.ettus.com >>>>>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >>>>> --- >>>>> Francois QUITIN >>>>> Assistant Professor >>>>> BEAMS Dpt. – Embedded Electronics >>>>> Brussels School of Engineering >>>>> Université Libre de Bruxelles (ULB) >>>>> Web https://sites.google.com/site/fquitin2/ >>>>> Phone +32 2 650 2829 >>>>> _______________________________________________ >>>>> USRP-users mailing list >>>>> USRP-users@lists.ettus.com >>>>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >>>> _______________________________________________ >>>> USRP-users mailing list >>>> USRP-users@lists.ettus.com >>>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >>> --- >>> Francois QUITIN >>> Assistant Professor >>> BEAMS Dpt. – Embedded Electronics >>> Brussels School of Engineering >>> Université Libre de Bruxelles (ULB) >>> Web https://sites.google.com/site/fquitin2/ >>> Phone +32 2 650 2829 > > --- > Francois QUITIN > Assistant Professor > > BEAMS Dpt. – Embedded Electronics > Brussels School of Engineering > Université Libre de Bruxelles (ULB) > > Web https://sites.google.com/site/fquitin2/ > Phone +32 2 650 2829 _______________________________________________ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
