[USRP-users] N310 phase jumps with 1 daughterboard

Rob Kossler rkossler at nd.edu
Mon Jan 27 14:21:51 EST 2020


Yes, I always use timed tune commands. If that were not happening
correctly, I don't think I could get consistent results with TwinRx.

I am presently using  I will complete the testing (using internal
LO) I've already begun with this version and then re-test some/all using
3.15.  Assuming that the results are different, it would seem that Ettus
should consider applying the fixes to the 3.14 branch.


On Mon, Jan 27, 2020 at 2:18 PM Nate Temple <nate.temple at ettus.com> wrote:

> 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
> 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
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