[USRP-users] N310 phase jumps with 1 daughterboard

Nate Temple nate.temple at ettus.com
Mon Jan 27 14:20:06 EST 2020


Hi Rob,

One other thing, if you're not on UHD v3.15.0.0, I'd recommend to update to
it. There was some phase reset and accumulator fixes with 3.15.0.0.

https://github.com/EttusResearch/uhd/blob/UHD-3.15.LTS/CHANGELOG#L44


Regards,
Nate Temple

On Mon, Jan 27, 2020 at 11:17 AM Nate Temple <nate.temple at ettus.com> wrote:

> Hi Rob,
>
> You should always use a tune request with a timed command when you want to
> align channels.
>
> One thing you could test is to try using the internal LO and see if you
> get different results.
>
> Also you could try using the integer N tuning mode, but I don't think it
> will make any difference for this issue. Checkout this great blog post on
> USRP tuning if you haven't seen it before that covers a few more tips on
> USRP tuning:
> http://www.radio-science.net/2017/12/adventures-in-usrp-tuning.html
>
> Regards,
> Nate Temple
>
> On Mon, Jan 27, 2020 at 9:33 AM Rob Kossler <rkossler at nd.edu> wrote:
>
>> Hi Nate,
>> I changed the subject as to not further hijack the other thread. Of the
>> 16 captures I collected, some of them included a tuning command (but using
>> the same timed commands I use for other devices such as TwinRx). But,
>> others did not.  For example, for the first two data points below (with
>> measured phase difference of -77 and -19 respectively).  I simply issued
>> two consecutive timed streaming commands.  So, I was very perplexed by the
>> results.
>>
>> In any event, I plan to re-take the data today both with and without a
>> DDC.  Hopefully, if I get rid of the DDC, I will see consistent phase
>> results, but we'll see.  Let me know if you have other ideas.
>> Rob
>>
>> On Mon, Jan 27, 2020 at 12:04 PM Nate Temple <nate.temple at ettus.com>
>> wrote:
>>
>>>
>>> @Rob: With the current init process of the N310, yes it is required to
>>> first set the external LO to 5 GHz.
>>>
>>> With regards to the offsets you're seeing, I believe you should only see
>>> a possible phase difference of 180* within the two channels on the same DB.
>>> Are you issuing a tune request at the start of streaming?
>>>
>>> Regards,
>>> Nate Temple
>>>
>>> On Mon, Jan 27, 2020 at 8:20 AM Rob Kossler via USRP-users <
>>> usrp-users at lists.ettus.com> wrote:
>>>
>>>> Robert, Sammy,
>>>> I am presently running some tests which compare the X310/TwinRx and the
>>>> N310 with regard to channel-to-channel phase.  In my setup, I have a signal
>>>> source that is split 8 ways (1:8 splitter) to feed the 4 channels of my
>>>> TwinRx and 4 channels of my N310. I have seen some strange behavior of the
>>>> N310 that perhaps Robert has experienced?  Take a look:
>>>>
>>>>    - For the TwinRx (for which I am a more experienced user with LO
>>>>    sharing), I get consistent channel-to-channel phase difference among all
>>>>    channels. This is true regardless of power cycles, re-starts of UHD, etc.
>>>>    - For the N310 (for which I am a beginner when it comes to external
>>>>    LO operation)
>>>>       - it seems more complex to run in this mode (as compared to
>>>>       TwinRx).  In order to get it to work, I have had to disable startup QEC
>>>>       calibration because it seems that the N310 initial cal occurs at 2500 MHz
>>>>       RF such that I would need to have my external LO at 5000 MHz for startup
>>>>       (during the UHD deveice 'make') and then later switch my external LO to the
>>>>       desired RF*2. Is this true?
>>>>       - when I run with either external LO or internal LO, I see
>>>>       inconsistent channel-to-channel phase results even between the two channels
>>>>       of a given daughterboard that share the same LO.  I do not understand how
>>>>       this is possible.  My results over 16 captures (with some re-starts of UHD,
>>>>       device reboots, and switching between internal/external LO) show the
>>>>       following channel-to-channel phase difference between channels 0 and 1
>>>>       which share the same LO: (values in degrees) -77, -19, -77, -19, -77, -19,
>>>>       -19, 39, -19, -19, -77, -19, -77, 39, -19, -19.  Note that there are only 3
>>>>       unique values and the delta happens to be 58 deg, but I don't know what
>>>>       that implies...
>>>>
>>>> Rob
>>>>
>>>>
>>>>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/attachments/20200127/03914b6a/attachment.html>


More information about the USRP-users mailing list