Thanks, Rob and Marcus.
A single tone is repeatedly transmitted to make a continuous stream out of the
Tx antenna. It is periodically sampled in Rx; the interval is about 1s. The
sample time is aligned with the beginning of the transmitted signal to make
sure we sample at the same time across antennas. We calculate the angle of the
first complex sample of capture to evaluate the signal phase.
I agree with you that there can be some phase wobble between the 10M ref
signals applied to PLLs in two devices because of temperature or other random
factors, however, inside a USRP, there are four independent PLLs for 2 Tx and 2
Rx. The 10M ref signals to them should also be wobbling. But my measurements
show that within the same USRP, phase is pretty stable between Tx and Rx. Any
explanation on this?
Kind regards.Hongwei
On Wednesday, 1 May 2024 at 20:34:15 BST, Marcus D Leech
<patchvonbr...@gmail.com> wrote:
It’s also why you can’t get tight instantaneous phase alignment between two
GPSDO devices even when on the same antenna.
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.
Rob
On Wed, May 1, 2024 at 11:04 AM zhou via USRP-users
<usrp-users@lists.ettus.com> wrote:
On Wednesday, 1 May 2024 at 15:15:12 BST, Marcus D. Leech
<patchvonbr...@gmail.com> wrote:
On 01/05/2024 10:11, zhou via USRP-users wrote:
Hi Marcus,
Thanks for your response.
"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 ?
It is OctoClock GPSDO, and Internal is used.
On Wednesday, 1 May 2024 at 14:19:44 BST, Marcus D. Leech
<patchvonbr...@gmail.com> wrote:
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:
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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