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

---

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


The REF OUT and PPS OUT ports aren't actually fully supported in the FPGA code, and we don't, at this point, recommend their use.



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