# Re: Synchronizing 3 USRP-N200 **URL:** \ **Category:** GNU Radio\ **Created:** [April 3, 2013, 6:29pm UTC](https://www.ruby-forum.com/t/re-synchronizing-3-usrp-n200/227919 "2013-04-03T18:29:47Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Zooz\_E](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/z/b19c9b/32.png) [@Zooz\_E](https://www.ruby-forum.com/u/Zooz_E)\ **Post date:** [April 3, 2013, 6:29pm UTC](https://www.ruby-forum.com/t/re-synchronizing-3-usrp-n200/227919/1 "2013-04-03T18:29:47Z")
Hi Marcus, Thanks for replying. I did the following test after your comments: 1- to rule out the scope sink problem, I used a file sink and plotted the output using octave: Same results observed. 2- I took the outputs of the splitters to the oscilloscope and there are aligned. Are there other ways to test Ref/PPS other than the one I mentioned in my original mesage? Best/ Zo ---
**Author:** ![Zooz\_E](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/z/b19c9b/32.png) [@Zooz\_E](https://www.ruby-forum.com/u/Zooz_E)\ **Post date:** [April 3, 2013, 9:00pm UTC](https://www.ruby-forum.com/t/re-synchronizing-3-usrp-n200/227919/2 "2013-04-03T21:00:24Z")
Zo, Have you tried swapping cables between USRP’s? both REF/PPS and signal (one at a time) to see if the apparent phase differences follow particular cables/signal paths? ---
**Author:** ![Zooz\_E](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/z/b19c9b/32.png) [@Zooz\_E](https://www.ruby-forum.com/u/Zooz_E)\ **Post date:** [April 4, 2013, 10:38am UTC](https://www.ruby-forum.com/t/re-synchronizing-3-usrp-n200/227919/3 "2013-04-04T10:38:25Z")
Dear Ian and All, Although I tried what you have said, the phase is random and different every time I run the flow graph. I deeply suspect that synchronization is actually done on the boards. I use a GPS receiver for synchronization and yesterday I noticed that the shape of the PPS signal is as the one in the attached image. I am afraid that the ripple and the overshoot can imitate the behavior of the PPS in much smaller period than one sec. Do you believe so? Can I use a usual function generator for the PPS instead of the GPS receiver? In other words, should the ref/pps signal be sync? Best regards, Zo Subject: Re: [Discuss-gnuradio] Synchronizing 3 USRP-N200 From: removed\_email\_address@domain.invalid Date: Wed, 3 Apr 2013 11:59:20 -0700 CC: removed\_email\_address@domain.invalid To: removed\_email\_address@domain.invalid Zo,Have you tried swapping cables between USRP’s? both REF/PPS and signal (one at a time) to see if the apparent phase differences follow particular cables/signal paths? On Apr 3, 2013, at 2:32 AM, Zooz E. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:Hi Marcus, Thanks for replying. I did the following test after your comments: 1- to rule out the scope sink problem, I used a file sink and plotted the output using octave: Same results observed. 2- I took the outputs of the splitters to the oscilloscope and there are aligned. Are there other ways to test Ref/PPS other than the one I mentioned in my original mesage? Best/ Zo\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Discuss-gnuradio mailing list removed\_email\_address@domain.invalid [https://lists.gnu.org/mailman/listinfo/discuss-gnuradio](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) ---
**Author:** ![Zooz\_E](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/z/b19c9b/32.png) [@Zooz\_E](https://www.ruby-forum.com/u/Zooz_E)\ **Post date:** [April 4, 2013, 11:17am UTC](https://www.ruby-forum.com/t/re-synchronizing-3-usrp-n200/227919/4 "2013-04-04T11:17:34Z")
First you need to ensure that the measurement of your pps signal shows the reality, and is not some measuring error. Then you can try to calm down the signal with some resistors, in the usual way when a rising edge overshoots… 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 Zooz Engineer Sent: Thursday, April 04, 2013 10:37 AM To: Ian B. Cc: removed\_email\_address@domain.invalid Subject: Re: [Discuss-gnuradio] Synchronizing 3 USRP-N200 Dear Ian and All, Although I tried what you have said, the phase is random and different every time I run the flow graph. I deeply suspect that synchronization is actually done on the boards. I use a GPS receiver for synchronization and yesterday I noticed that the shape of the PPS signal is as the one in the attached image. I am afraid that the ripple and the overshoot can imitate the behavior of the PPS in much smaller period than one sec. Do you believe so? Can I use a usual function generator for the PPS instead of the GPS receiver? In other words, should the ref/pps signal be sync? Best regards, Zo * * * Subject: Re: [Discuss-gnuradio] Synchronizing 3 USRP-N200 From: removed\_email\_address@domain.invalid Date: Wed, 3 Apr 2013 11:59:20 -0700 CC: removed\_email\_address@domain.invalid To: removed\_email\_address@domain.invalid Zo, Have you tried swapping cables between USRP’s? both REF/PPS and signal (one at a time) to see if the apparent phase differences follow particular cables/signal paths? On Apr 3, 2013, at 2:32 AM, Zooz E. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: Hi Marcus, Thanks for replying. I did the following test after your comments: 1- to rule out the scope sink problem, I used a file sink and plotted the output using octave: Same results observed. 2- I took the outputs of the splitters to the oscilloscope and there are aligned. Are there other ways to test Ref/PPS other than the one I mentioned in my original mesage? Best/ Zo