[USRP-users] N310 phase jumps with 1 daughterboard

Rob Kossler rkossler at nd.edu
Mon Jan 27 12:33:23 EST 2020


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/20200127/20f950bc/attachment.html>


More information about the USRP-users mailing list