# Phase synchronizing USRPs in GNU Radio **URL:** \ **Category:** GNU Radio\ **Created:** [September 15, 2014, 7:28am UTC](https://www.ruby-forum.com/t/phase-synchronizing-usrps-in-gnu-radio/232035 "2014-09-15T07:28:57Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\ **Post date:** [September 15, 2014, 7:28am UTC](https://www.ruby-forum.com/t/phase-synchronizing-usrps-in-gnu-radio/232035/1 "2014-09-15T07:28:57Z")
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 ---
**Author:** ![sarankumar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/e36b37/32.png) [@sarankumar](https://www.ruby-forum.com/u/sarankumar)\ **Post date:** [September 15, 2014, 3:37pm UTC](https://www.ruby-forum.com/t/phase-synchronizing-usrps-in-gnu-radio/232035/2 "2014-09-15T15:37:53Z")
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](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 ---
**Author:** ![sarankumar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/e36b37/32.png) [@sarankumar](https://www.ruby-forum.com/u/sarankumar)\ **Post date:** [September 15, 2014, 3:44pm UTC](https://www.ruby-forum.com/t/phase-synchronizing-usrps-in-gnu-radio/232035/3 "2014-09-15T15:44:43Z")
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: > [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) [1] Links: