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. - 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 >
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