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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