On 01/05/2024 08:25, zhou via USRP-users wrote:
Hi All,
I am trying to use 4Rx and 4Tx antennas from two X310 USRPs. I hope
the received signals have stable phase relationship but they don't
seem to be. I am wondering why and how to fix it.
I measured the phase using the connection as below:
Inline image
cos(t)+i*sin(t) signal is split into and received on four Rx antennas.
Two X310s are connected to the same OctoClock for 10MHz Ref and PPS.
Tx and Rx commands are all timed. The measurement results are as below:
The Tx signal is continuous during test. I measured phase every second
for 20 sec. In the 2nd USRP, the phases are stable on both antennas
while it is not in the 1st. If I change the Tx signal to the 1st USRP,
then the results swap - phases become stable in the 1st USRP and
unstable in the 2nd.
My first though was that there might be small CFO between USRPs even
though both are connected to the OctoClock, but CFO should have caused
linear change. Here, the phase offset is not linear and kind of random
within 20 second measurement.
What can be the reason? Any suggestion will be appreciated.
Kind regards,
H.
Are you setting up clocking identically for both USRPs? That is
setting the reference clock to "external" and the 1PPS source to
"external" on both devices? Are you using a single multi_usrp object
for all RX channels?
What type of daughtercards are in your X310?
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