[USRP-users] LO phase alignment

Matt Ettus matt at ettus.com
Fri Jun 22 13:49:15 EDT 2012


To clarify here, as long as all LOs are tuned at the same time, you
will always get the same phase offset.  If you retune one, you have to
retune the others simultaneously.

Matt

On Fri, Jun 22, 2012 at 1:58 AM, Christophe ALEXANDRE
<christophe.alexandre at cnam.fr> wrote:
> Hi Josh,
>
> i've read the link :
>
> Using timed commands, multiple frontends can be tuned at a specific time.
> This timed-tuning ensures that the phase offsets between VCO/PLL chains will
> remain constant after each re-tune. See notes below:
>  a.. There is a random phase offset between any two frontends
>  b.. This phase offset is different for different LO frequencies
>  c.. This phase offset remains constant after retuning
>   a.. Due to divider, WBX phase offset will be randomly +/- 180 deg after
> re-tune
>  d.. This phase offset will drift over time due to thermal and other
> characteristics
>  e.. Periodic calibration will be necessary for phase-coherent applications
> I still don't understand the principle you use. is it a VCO special property
> ?
>
> some questions still remain :
>
> Q1) if i change LO freq from f1 to f2 then back to f1, should i get the same
> phase offset on f1 ?
>
> Q2) if i turn off the N210s then on, should i get the same offset on the
> same freq ?
>
> Q3) if the Q1, Q2 answers are yes, what kind of phase offset precision
> should i expect ?
>
>
>
> 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: "Josh Blum" <josh at ettus.com>
> To: <usrp-users at lists.ettus.com>
> Sent: Thursday, June 21, 2012 5:53 PM
>
> Subject: Re: [USRP-users] LO phase alignment
>
>
>>
>>
>> On 06/21/2012 08:48 AM, Christophe ALEXANDRE wrote:
>>>
>>> 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 ?
>>>
>>
>> Does this example help:
>>
>> http://files.ettus.com/uhd_docs/manual/html/sync.html#align-los-in-the-front-end-sbx-wbx-n-series
>>
>>> can i use this new feature using gnuradio ?
>>>
>>
>> Yes
>>
>>> do you have any example (even C++ example) showing how to use it ?
>>>
>>
>> Link above.
>>
>> -josh
>>
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>
>
>
>
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