On 03/11/2022 09:36, Rob Kossler wrote:
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
Thanks, Rob. I had, once again, forgotten about the initial-5GHz
requirement.
The complete list of possible "init" and "tracking" CAL options is here:
https://files.ettus.com/manual/page_usrp_n3xx.html#n3xx_mg_calibrations
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?
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