[USRP-users] LO phase alignment

Christophe ALEXANDRE christophe.alexandre at cnam.fr
Thu Jun 21 11:48:41 EDT 2012


hi John,

i have already read this app note (in fact, i have started with it). 
I've only seen a star after phase on table 2 for SBX but no more info.

what is the basic principle used to solve the phase alignment problem ?

can i use this new feature using gnuradio ?

do you have any example (even C++ example) showing how to use it ?
 
 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 
 FRANCE     
 email : christophe.alexandre at cnam.fr               
 tel. 0140272699 
 mob. 0651087311
 fax. 0140272994    
 

  ----- Original Message ----- 
  From: John Malsbury 
  To: usrp-users at lists.ettus.com 
  Sent: Thursday, June 21, 2012 4:33 PM
  Subject: Re: [USRP-users] LO phase alignment


  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
schedule.
http://files.ettus.com/uhd_docs/doxygen/html/classuhd_1_1usrp_1_1multi__usrp.html#a191b78b00d051d3d51c2f719361c1fb5
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.

  -John



  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 DriverT), 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 
     FRANCE     
     email : christophe.alexandre at cnam.fr               
     tel. 0140272699 
     mob. 0651087311
     fax. 0140272994    
     


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