This is true of any pair of PLL synthesizers even when using a shared reference.
My next question was going to be “how is phase measured?”
Sent from my iPhone
On May 1, 2024, at 2:12 PM, Rob Kossler <rkoss...@nd.edu> wrote:
The 10 MHz ref supplied to each X310 device is used in a PLL in each device to obtain the 10MHz ref used for that device (and for disciplining the various LOs on the device). Thus, there is a relative phase "wobble" between the 10MHz ref signals used on each device as each PLL continuously adjusts to maintain disciplined output. Over time, this averages out to zero. But, instantaneously, it is not. So, my question is: how instantaneous is your phase measurement? If you instead calculate a phase averaged over numerous samples, can you get a consistent result? From your plot, it looks like this is true.
"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?"
Yes, I use multi_usrp
multi_usrp::make('addr0=192.168.12.2,second_addr0=192.168.13.2,addr1=192.168.14.2,second_addr1=192.168.15.2,master_clock_rate=184.32e6')
"external"
set for both ref and pps:
usrp->set_clock_source("external")
usrp->set_time_source("external")
I think this should automatically set both devices.
"What
type of daughtercards are in your X310?"
UBX
Kind regards.
And, to clarify, this is an Octoclock-G, and not a plain Octoclock ?
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:
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?
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