On 04/11/2022 16:21, Kenneth Burchfield wrote:
Rob / Marcus,
The initial-5GHz LO was my problem. I was not providing it at
startup. Thank you guys for the info. The mirroring is resolved!
-Scott
That's excellent!
On Thu, Nov 3, 2022 at 8:48 AM Marcus D. Leech
<patchvonbr...@gmail.com> wrote:
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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