[USRP-users] N310 phase jumps with 1 daughterboard

Nate Temple nate.temple at ettus.com
Mon Jan 27 14:17:17 EST 2020


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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