On 09/15/2018 11:54 PM, Koyel Das (Vehere) wrote:
I just forwarded in another thread the processing I am doing. Have you
received it?
Regards,
Koyel
Yes, but I'd rather not have to analyse your MATLAB code in detail.
You can use the --phase-relations option on the uhd_fft utility for
doing two-channel phase-coherence measurements in real-time.
Unless something is horribly broken, two UBX cards on the same
underlying USRP platform WILL operate with mutual coherence, with
some initial phase-offset, just due to the way synthesizers work. But
that phase offset will carry-forward in time, with only very minor
phase noise perturbations just due to the physics of semiconductors, etc.
------------------------------------------------------------------------
*From:* Marcus D. Leech <mle...@ripnet.com>
*Sent:* Sunday, September 16, 2018 9:05:29 AM
*To:* Koyel Das (Vehere); 'USRP-users@lists.ettus.com'
*Subject:* Re: [USRP-users] Sampler clock common or not?
On 09/15/2018 11:32 PM, Koyel Das (Vehere) wrote:
I don’t have access to the flowgraph currently but it’s the same
flowgraph I sent earlier in my other previous email for 2955 R. I
have UHD with two channels, each channel connected to a file sink.
One channel is set to TX/RX, another to RX2. I am sampling at 1 msps.
I am capturing data from two channels, storing in file and then
reading them in matlab and cross correlating them to get phase
difference but the phase difference for any particular frequency bin
is showing deviations with time. Deviations are huge sometimes +-pi.
Regards,
Koyel
I would say that you're doing something wrong in the post-processing.
I routinely use USRPs of all types for interferometry in radio
astronomy, where the long term phase noise has to be very low, or your
data is rubbish.
------------------------------------------------------------------------
*From:* Marcus D. Leech <mle...@ripnet.com> <mailto:mle...@ripnet.com>
*Sent:* Sunday, September 16, 2018 8:48:26 AM
*To:* Koyel Das (Vehere); 'USRP-users@lists.ettus.com
<mailto:USRP-users@lists.ettus.com>'
*Subject:* Re: [USRP-users] Sampler clock common or not?
On 09/15/2018 10:38 PM, Koyel Das (Vehere) wrote:
Hi,
Thanks for the information. Do I have to set any property in the gnu
radio uhd to phase lock the two oscillators to on board clock or
they are by default locked to it?
Nothing special to do. It happens automatically.
Can the external reference be gps? What settings need to be done in
UHD to sync the two oscillators to gps?
There's a good knowledge-base article on this and many other topics here:
https://kb.ettus.com/Synchronization_and_MIMO_Capability_with_USRP_Devices
Actually I am receiving a stationary signal using two ports TX/RX
and RX2 but I am not getting a constant phase difference with time.
It can happen if two oscillators are not synced .
The starting phase between the two sides will not be anything in
particular.
But after that, they'll have a constant phase difference. What are
you using to measure the phase different between the two channels.
How is the signal delivered to the two channels?
Can you share your Gnu Radio flow-graph?
Please help.
------------------------------------------------------------------------
*From:* USRP-users <usrp-users-boun...@lists.ettus.com>
<mailto:usrp-users-boun...@lists.ettus.com> on behalf of Marcus D.
Leech via USRP-users <usrp-users@lists.ettus.com>
<mailto:usrp-users@lists.ettus.com>
*Sent:* Sunday, September 16, 2018 5:10:23 AM
*To:* usrp-users@lists.ettus.com <mailto:usrp-users@lists.ettus.com>
*Subject:* Re: [USRP-users] Sampler clock common or not?
On 09/15/2018 01:35 AM, Koyel Das (Vehere) via USRP-users wrote:
Hi,
I am using USRP 2954R. I have connected one antenna to RX2 of RF0
and another antenna to TX/RX of RF1. Both are used for receiving.
Can someone tell me if RX2 of RF0 and TX/RX of RF1 are phase locked
that is the signal received by the two have a constant phase
difference with time or not? Are the two LOs controlled by a common
master oscillator or two LOs run Independently?
Regards,
Koyel
Both synthesizers are phase-locked to either the on-board clock, or
an external reference clock, if you're using an external reference.
So, they'll
have no relative phase-drift with respect to one another (except
for thermal effects, but those have a very small magnitude).
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