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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