[USRP-users] LO phase alignment

John Malsbury john.malsbury at ettus.com
Thu Jun 21 10:33:01 EDT 2012

This feature is currently supported in the master branch.  I will update 
the document when it is moved to release.  If you search the list 
archives, you can find some information on how to use this feature.  
Here's a quote from one such e-mail sent by Josh Blum:

"Use set_command_time and clear_command_time around any call you wish to

Note that this will remove the tune-to-tune offset variations.  But you 
will probably still need to perform some level of calibration and expect 
this to change a bit with temperature, etc.  I'd recommend reading the 
mimo and sync app note on the kb as well.


On 06/21/2012 07:27 AM, Christophe ALEXANDRE wrote:
> Hi all,
> i want to use 2 x (N210 + SBX) for a laser telemetry application.
> i need to synchronize clocks, align sample times and also have precise 
> knowledge
> of LO phase difference between both N210s.
> At the moment, using a mimo cable, i use the following
> method : i generate a 1.00005 GHz and inject it on both N210s
> with a center frequency equal to 1 GHz.
> I get 2 exact 50 kHz complex signals with a constant phase difference. 
> Each time
> i start a measure, i get an other phase difference, still constant.
> if i change the frequency from 1 GHz to 1.1 GHz then go back
> to 1 GHz, the phase difference has changed.
> I can't use this for a telemetry application.
> i have read this application note :
> http://www.ettus.com/content/files/kb/Selecting_an_RF_Daughterboard.pdf
> and find this :
> _Do I plan to implement beamforming or direction finding (DF) 
> capability? _
> While all daughterboards can be used in a MIMO configuration, this 
> does not necessarily imply there is phase alignment between the RF 
> chains of one or more daughterboards. The BasicRx, BasicTX, LFRX and 
> LFTX are exceptions to this, since they do not include local 
> oscillators that contribute to phase ambiguity between channels.
> The Ettus Research SBX daughterboard utilizes an RF PLL that includes 
> a resynchronization feature, which can be used to align the LOs across 
> multiple SBXs, and multiple USRP hardware devices. Using the
> UHD (USRP Hardware Driver^(TM)), timed SPI commands can drive this 
> re-synchronization feature. At the time of this writing, this feature 
> is not supported in the mainline UHD. However, this feature is planned 
> for release in 2012.
> I can't work without phase alignment. So my question is :
> *when could we get this feature in UHD ?*
>  regards.
>  Christophe ALEXANDRE
>  Conservatoire National des Arts et Métiers (CNAM)
>  Laboratoire CEDRIC-LAETITIA
>  Département EASY
>  Accès 17-1-32, Case 2D2P10
>  292 rue Saint Martin
>  75141 PARIS CEDEX 03
>  email : christophe.alexandre at cnam.fr 
> <mailto:christophe.alexandre at cnam.fr>
>  tel. 0140272699
>  mob. 0651087311
>  fax. 0140272994
> _______________________________________________
> USRP-users mailing list
> USRP-users at lists.ettus.com
> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com

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