# Synchronizing two USRP2

**URL:** <https://www.ruby-forum.com/t/synchronizing-two-usrp2/180180>\
**Category:** GNU Radio\
**Created:** [December 14, 2009, 7:29am UTC](https://www.ruby-forum.com/t/synchronizing-two-usrp2/180180 "2009-12-14T07:29:35Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![laserzt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/df705f/32.png) [@laserzt](https://www.ruby-forum.com/u/laserzt)\
**Post date:** [December 14, 2009, 7:29am UTC](https://www.ruby-forum.com/t/synchronizing-two-usrp2/180180/1 "2009-12-14T07:29:35Z")

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## I understand that this can be done, by an external clock (GPS diciplined OCXO), with the 10Mhz and 1PPS inputs. is there any way I can tell the two usrp2’s to start together, instead of using the timestamps to synchronize them?

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**Author:** ![laserzt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/df705f/32.png) [@laserzt](https://www.ruby-forum.com/u/laserzt)\
**Post date:** [December 14, 2009, 8:21am UTC](https://www.ruby-forum.com/t/synchronizing-two-usrp2/180180/2 "2009-12-14T08:21:41Z")

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> I understand that this can be done, by an external clock (GPS diciplined  
> OCXO), with the 10Mhz and 1PPS inputs.  
> is there any way I can tell the two usrp2’s to start together, instead of  
> using the timestamps to synchronize them?

Hi,

There is a start streaming at command  
([http://lists.gnu.org/archive/html/discuss-gnuradio/2009-06/msg00260.html](http://lists.gnu.org/archive/html/discuss-gnuradio/2009-06/msg00260.html))  
which can be used to receive synchronously.

Cheers,

Christoph

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**Author:** ![laserzt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/df705f/32.png) [@laserzt](https://www.ruby-forum.com/u/laserzt)\
**Post date:** [December 16, 2009, 12:58am UTC](https://www.ruby-forum.com/t/synchronizing-two-usrp2/180180/3 "2009-12-16T00:58:11Z")

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Cheers for that Christoph, beats my post processing with timestamps fix!

For what its worth I’ve gotten away with fairly cheap TCXO’s (£15  
generic  
farnell ones) and a GPSDO circuit like the one at  
[VE2ZAZ - GPS-Derived 10MHz Frequency Standard](http://ve2zaz.net/GPS_Std/GPS_Std.htm) (it did need some manual tuning at  
first as the oscillators werent within the frequency locking range from  
a  
cold start) - you do get what you pay for with (double) ovenized CXO’s  
ones  
though. You tend to find them on the commericial boards (theres a  
mailing  
list post somewhere linking to a few options)

Tim

On Mon, Dec 14, 2009 at 7:16 AM, Christoph T. \<

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**Author:** ![laserzt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/df705f/32.png) [@laserzt](https://www.ruby-forum.com/u/laserzt)\
**Post date:** [December 16, 2009, 2:31pm UTC](https://www.ruby-forum.com/t/synchronizing-two-usrp2/180180/4 "2009-12-16T14:31:06Z")

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Tim P. wrote:

> Tim

FYI - I believe the patch has been merged into the current git master -  
so you if you’re tracking the git source you don’t need to manually  
apply the patch anymore.  
Doug

–  
Douglas G.  
Code 5545  
U.S. Naval Research Laboratory  
Washington, DC 20375  
(202) 767-9048  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)