[USRP-users] N310: Channel pairs are drifting in phase whith external LO setup

Janos Buttgereit janos.buttgereit at fh-muenster.de
Fri Mar 22 10:40:24 EDT 2019


Thank you for the quick reply, that did the trick, at least half way. 

Now I’m struggling with the random 180° phase offset between the front end pairs, obviously generated by the AD9371 chip according to my research. Is there any best-practice in detecting this phase shift that does not involve an additional reference signal source?

> Am 22.03.2019 um 14:17 schrieb Marcus D. Leech via USRP-users <usrp-users at lists.ettus.com>:
> 
> On 03/22/2019 05:31 AM, Janos Buttgereit via USRP-users wrote:
>> Hi,
>> 
>> after having struggled a lot with network config issues I finally got out N310 up and running. We chosed it for an application that needs perfectly constant phases between all four channels to build up DOA estimation applications.
>> 
>> I’ve set up an N210 as a signal source, outputting a sine round about 1.5GHz feeding a 4-way splitter that than feeds all four input channels of the N310. A Rhode&Schwarz signal generator outputting a 3GHz sine wave feeds a two way splitter that is connected to both external rx LO inputs.
>> 
>> From this setup I expect all four channels to maybe have a static phase offset that does not change over time. However, it can be noticed that the pairs of channels 0 and 1 and the pairs of channels 2 and 3 show those behavior but both pairs drift against each other over time. Any idea of what could be wrong with this setup?
>> 
>> I attached the GNURadio flow graph for this setup.
>> 
>> Thanks in Advance!
>>  
> Change the "Sync" option to "Unknown PPS".   Why this is required is a bit of a mystery, but another user experienced the same issue.
> 
> The N310 is conceptually two radios in a single box, and each radio within the FPGA has its own "timekeeper".  For some reason, unless those
>  "timekeepers" are started synchronized with each other, sample timestamps drift relative to one another.  This should not be the case, but
>  it appears to be.
> 
> 
> 
> 
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