When running N310 with external LO, the device will automatically try to run a calibration at device startup (actually in the software make N310 device) where it expects the external LO to be at 5 GHz. If you supply an LO at a different frequency, this calibration will be ruined. Is it possible that you are not supplying a 5 GHz LO at startup? Note that you can change it after startup to your desired freq of operation.
And, responding to another discussion point about QEC correction, even if you disable the "tracking cal" you can keep the "init cal" in place. I assume this means that an initial calibration is performed and then the calibrated gain/phase settings are left untouched afterwards. So, disabling the tracking cal should not mean that you are not performing any correction - just not updated dynamically. Rob On Wed, Nov 2, 2022 at 4:28 PM Marcus D. Leech <patchvonbr...@gmail.com> wrote: > On 02/11/2022 15:53, Kenneth Burchfield wrote: > > Marcus, > I agree. Is there a way to tune the sideband suppression so that I can > attenuate more of the mirrored signal? > With the internal lo, everything seems to just work. Are there extra > configuration steps that I need to take to adjust for the external lo? > > I'm trying to find that out now. > > I suspect that spending an afternoon with the AD9371 datasheet might > provide some clues--but as to whether those are > actually exposed in UHD is another question. > > With the internal LO, the chip has internal algorithms for optimizing > phase and amplitude balance. Those algorithms aren't > "in play" when you use an external LO, apparently. > > One thing that *could* be done, but is tedious, is to adjust the phase and > amplitude balance of the baseband signal to > compensate for the imbalance of the mixer. This is basically what the > internal algorithms in the chip are doing, as > far as I can tell. > > > > Thanks, > Scott > > On Wed, Nov 2, 2022 at 2:41 PM Marcus D. Leech <patchvonbr...@gmail.com> > wrote: > >> On 02/11/2022 15:27, Kenneth Burchfield wrote: >> >> Marcus, >> >> The sidebands do not change with the LO level. >> >> I am basically running the tx_waveforms example from UHD 4.2.0.0, and I am >> adding the argument tx_lo_source=external. Attached is a picture of the >> spectrum. I am generating a SINE with wave-freq input 2e6. The center spike >> is some LO leakage. The spike at -2e6 is the mirroring I am seeing. >> >> Thanks, >> Scott >> >> The LO suppression looks to be about 55dBc, which is not horrific. >> >> The sideband suppression appears to be only about 30dBc, which is not >> very good. >> >> >> >> On 02/11/2022 12:09, Scott Burchfield wrote: >> >> Hi, >> >> >> Are there any updates on this problem. I normally try not to reply to old >> threads, but I am seeing the same the same spectral mirroring Rob described >> earlier. My setup is also the same as Rob’s.I have tracked some newer >> threads that mentioned disabling TX_QEC_INIT, but I am still seeing the >> mirroring after disabling QEC. >> >> https://www.mail-archive.com/usrp-users@lists.ettus.com/msg07489.html >> >> Thanks, >> >> Scott >> >> >> It seems to me that if you use an external LO, that LO has to go through the >> phase-splitter on the mixer, and that phase-split is subject to >> errors, so turning off QEC may not be that desirable--although I think >> the mixer on the N310 (using an AD9371) >> >> is a 2XLO, so the phase error should be very very small. >> >> Do the unwanted sidebands change with LO level? >> >> >> > _______________________________________________ > USRP-users mailing list -- usrp-users@lists.ettus.com > To unsubscribe send an email to usrp-users-le...@lists.ettus.com >
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