Hi Serge, Are you measuring the phase offset between the TX0 and TX2 signals in a steady-state case, or the time difference in the start of those signals?
In the former case, your results could be impacted by the lack of internal LO sharing between daughterboards. I would fully expect an unknown phase offset between channels 0 and 2 every time you reconfigure the device. In the latter case, it sounds like a start trigger mismatch like Marcus mentioned. Can you share more details as to how you're measuring the phase offset? Thanks, -Daniel On Thu, Nov 8, 2018 at 5:30 AM Serge Malo via USRP-users < usrp-users@lists.ettus.com> wrote: > Yes: we are using UHD 3.13.1.0 RC1, with the latest file system image > > I can try to use lower tx start times to see if the time offset changes > with that. > > Thanks, > Serge > > On Wed, 7 Nov 2018 at 21:44, Marcus D. Leech <patchvonbr...@gmail.com> > wrote: > >> On 11/07/2018 09:31 PM, Serge Malo wrote: >> >> Yes: >> We only use one streamer for all RF outputs, and send time_spec with each >> call to the streamer's send method. >> We reset the internal time with set_time_unkown_pps(0), and program the >> first samples to be streamed at a time of 0.800s. >> It is basically the same code we used on the X300/X310. >> >> Thanks, >> Serge >> >> Well, that is quite strange--the magnitude of the time offsets is larger >> than I would expect. >> >> Perhaps someone from the N310 team can comment? >> >> Serge, are you using the latest UHD and system image versions for the >> N310? >> >> >> >> On Wed, 7 Nov 2018 at 21:03, Marcus D. Leech via USRP-users < >> usrp-users@lists.ettus.com> wrote: >> >>> On 11/07/2018 08:53 PM, Serge Malo via USRP-users wrote: >>> >>> Hi all, >>> >>> We are trying to send 4 synchronous signals from the 4 Tx ports of the >>> N310. >>> We are using UHD 3.13.1.0 RC1 under Ubuntu. >>> Central Freq = 1575.42 GHz and 1227.6 MHz >>> Master Clock rate = 153.6 MHz >>> >>> We would expect to have less than 3ns offset between all TX ports of the >>> N310, like we do with the X300/X310. However, we have measured 4700ns >>> between TX RF ports 0 and port 2. >>> We have tried the next things with no more success: >>> - Sampling rates of 25.6MSps, 38.4Msps, 76.8Msps >>> - Init with the device options "init_cals=ALL" and "force_reinit=1" >>> - Use the internal GPSDO >>> - Use clock_source=external and time_source=external (from an Octoclock). >>> >>> Can you tell us: >>> -What time offset between TX RF ports we should expect to achieve? >>> -Is there anything else we can try to reduce this offset to less than >>> 3ns? >>> >>> Best regards, >>> Serge >>> >>> >>> How are you setting up your TX streamer? Is it time-tagged to start at >>> a particular device time? >>> >>> >>> >>> _______________________________________________ >>> USRP-users mailing list >>> USRP-users@lists.ettus.com >>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >>> >> >> _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > -- Daniel Jepson Digital Hardware Engineer National Instruments O: +1.512.683.6163 daniel.jep...@ni.com
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