Hi Sam, Just tolerate it. I don't have any compensation algorithm. Rob On Tue, Mar 3, 2020 at 1:41 PM Sam Reiter <[email protected]> wrote:
> Rob, > > Question for you - is your usecase one where you can simply tolerate that > 180 degree ambiguity? Or do you have a routine in your code to characterize > and compensate for it on each run? > > Sam Reiter > > On Tue, Mar 3, 2020 at 11:44 AM Marcus D. Leech via USRP-users < > [email protected]> wrote: > >> On 03/03/2020 12:31 PM, Rob Kossler via USRP-users wrote: >> >> Hi Len, >> I have run some testing of this capability. A few remarks: >> >> - In my test setup, I had a signal generator running into a 1:4 >> splitter with outputs connected to the four N310 Rx2 inputs. I used >> another signal generator as the LO source running into a 1:2 splitter with >> outputs connected to the N310 Rx LO inputs with amplitude near 3 dBm >> <https://kb.ettus.com/N300/N310#Front_Panel> at N310 LO inputs. >> - When using external LO, the RF range is limited to a max of 4 GHz >> (rather than 6 GHz which is the limit with internal LO) >> - I had problems with UHD 3.14 because there was some bug related to >> resetting the phase of the DDC. I had success with 3.15. But even with >> success, there is still a 180 degree ambiguity between channels 1/2 and >> channels 3/4. I am not certain regarding the circumstances that can cause >> the ambiguity to flip, but I think it only occurs at application startup >> such that once your application is running, you can expect consistent >> results with no ambiguity flips. >> >> This is probably due to the 2XLO phase-splitter inside the AD9371 >> chips--it's based on a flip-flop, whose initial state is unpredictable. Any >> 2XLO phase-splitter has this property--including on the WBX >> daughtercard used on N210/X310 etc. The mixer has a 2XLO phase-splitter, >> so also shows this 180deg phase ambiguity. >> >> >> >> - When you launch your application and create a usrp device instance, >> the UHD software will automatically try to run some IQ calibrations >> (RX_QEC_INIT) expecting that the RF is at 2.5 GHz, which implies that your >> external LO must be at 5 GHz at startup. After startup is complete (and >> this calibration is complete) you can change the freq of your LO and >> retune >> the RF of the various channels keeping in mind that the external LO must >> always be twice the desired RF. If you want to avoid the startup >> calibration (with LO at 5 GHz), you can specify explicitly which >> calibrations >> <https://files.ettus.com/manual/page_usrp_n3xx.html#n3xx_mg_calibrations> >> you want using the device args and choose not to run RX_QEC_INIT. But, I'm >> not sure if skipping this calibration could have negative effects on >> signal >> quality. >> >> Let me know if you have questions. >> Rob >> >> >> On Thu, Feb 27, 2020 at 12:22 AM Len via USRP-users < >> [email protected]> wrote: >> >>> Folks, >>> I'm looking for information from any subscriber(s) to this forum that >>> have successfully used the USRP N310 to provide 4 Rx channels which are >>> both coherent and synchronized. I've heard this could be challenging and I >>> know people have been able to do this successfully so I was wondering where >>> I might find some detailed information/instructions on how best to >>> accomplish this. I was told this forum would be a good place to start. So >>> any block diagrams illustrating the Master LO and Master Clock hookups >>> needed along with any available calibration procedure(s) describing how to >>> actually check/verify coherence and synchronization between the 4 channels >>> would be great. >>> >>> >>> Thanks, >>> Len >>> _______________________________________________ >>> USRP-users mailing list >>> [email protected] >>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >>> >> >> >> _______________________________________________ >> USRP-users mailing >> [email protected]http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> >> >> _______________________________________________ >> USRP-users mailing list >> [email protected] >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> >
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