Phase synchronizing USRPs in GNU Radio

GNU Radio
1

Hi all,

I am trying to phase synchronize multiple usrp’s using 10 MHz reference
and
1 pps. I was able to get them synchronised but with constant phase
offset
between. But every time I retune or rerun the flowgraph the phase offset
changes. how can I estimate and compensate the phase offset between
USRPs
without rerunning or retuning USRP? The purpose is to do DOA estimation.
I
use WBX daughterboard and USRP N210.

Regards,
Saran

2

As far as I know this phase error is caused by the PLL concept that does
not care for the phase of the reference to build the output signal
always with reproducible phase relation to the reference.

So you will have to find some workaround like an auto align procedure,
or use another transceiver concept that keeps the phase consistent
through the whole path, from the reference to the output carrier.

Ralph.

From: discuss-gnuradio-bounces+ralph=removed_email_address@domain.invalid
[mailto:discuss-gnuradio-bounces+ralph=removed_email_address@domain.invalid] On Behalf Of
sarankumar
Sent: Monday, September 15, 2014 7:27 AM
To: GNURadio D.ion List
Subject: [Discuss-gnuradio] phase synchronizing USRPs in GNU Radio

Hi all,

I am trying to phase synchronize multiple usrp’s using 10 MHz reference
and 1 pps. I was able to get them synchronised but with constant phase
offset between. But every time I retune or rerun the flowgraph the phase
offset changes. how can I estimate and compensate the phase offset
between USRPs without rerunning or retuning USRP? The purpose is to do
DOA estimation. I use WBX daughterboard and USRP N210.

Regards,

Saran

3

The “timed command” concept in UHD allows multiple N2xx with SBX or WBX
to be phase-aligned on tuning, using a special “resynch”

hardware feature of the synthesizers used (ADF4351). However, this
functionality is not exposed in the gr-uhd interface.

Furthermore, on the WBX, even with timed commands there will be a 180deg
phase-ambiguity, due to the 2XLO mixer. The units will

either be in-phase with each other, or exactly 180deg out-of-phase with
each other, since the state of the divider in the 2XLO mixer cannot

be controlled from the outside.

On 2014-09-15 09:36, Ralph A. Schmid, dk5ras wrote:

[email protected]
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