On 2022-10-26 16:03, Brian Padalino wrote:
After a bunch of testing, I ended up with the following solution which
seems to have fixed the vast majority of the issue. There's still
extra noise, but not nearly as bad as it was previously so I'd
appreciate it if Ettus still looked into a more complete solution.
For now, I just enabled the "mute till lock detect" feature of the
ADF5356 and ADF4351 PLLs. I modified gen_adf5356_regs.py and
gen_adf4351_regs.py to default it to be on, and the ld_cyc_count to be
the longest possible.
Brian
Hmm, interesting. This is basically a "smoking gun" that it's the
actual synthesizer outputs, rather than some digital signalling--
which you'd previously all-but-eliminated.
Interestingly, the switches used on the synthesizer outputs are
high-isolation, non-reflective switches, providing about
60dB of port-to-port isolation, and terminating the
switched-away-from port to reduce tendency for lines to radiate.
I'm kind of getting lost in the schematic, but I wonder if there's a
case where the switches are actually in the wrong state?
My guess is that if this is a "sneak path" issue, it will require a
hardware rev to fix, but if it's just a combination of
muting the synthesizers during tuning, combined, perhaps, with a
slightly-wrong truth table for the various RF switches
in the design, that's just software.
On Wed, Oct 26, 2022 at 9:38 AM Brian Padalino <bpadal...@gmail.com>
wrote:
Hey Wan,
On Tue, Oct 25, 2022 at 10:53 PM Wan Liu <wan....@ettus.com> wrote:
Hello Brian,
Thank you for the additional information.
Regarding #6, I meant that if you have two TwinRX
daughterboards, see if you get this problem when the fixed
channel is on one daughterboard, and the tuned channel is on
the other.
Ah, I see. Unfortunately my setup is a mixed USB/TwinRX setup so
maybe it isn't exactly testing what you're asking for, but I did
use the subdev spec to target the UBX RX2 for hopping around, and
the TwinRX Channel 0 was fixed. In this case, the fixed spectrum
stayed nice and clean the whole time.
Regarding screenshots, are you referring to any particular
frequency and time region, or is everything above the noise
floor associated with the tuning? In other words, is the clean
spectrum where there is nothing above the noise floor in both
time and frequency plots?
The captures were taken with terminated RF inputs. Channel 0 of
the TwinRX was fixed at some frequency (I believe 400 MHz) and
Channel 1 was hopping around. The recording was observing Channel
0 - the fixed frequency channel. When no hopping happens, there
is clean spectrum with just a noise floor which is what I expected
to see. When hopping is happening, every so often we will see
these sweeping signals show up. They last around 10 ms or so and
then the spectrum is back to being clean.
Also can you explain what you mean by "shows some analog
PLL-style locking for around 10 ms of time, then goes away"?
Are you referring to the burst from 3 ms to 13 ms, or
something specifically at 10 ms?
I meant the phenomenon that starts at around 3 ms and lasts until
around 13 ms. It looks like an analog PLL settling to me. Here
is a zoomed in version:
https://drive.google.com/file/d/1NDax78i3UQh7X_R4g8SHBkBLibI1ICQZ/view?usp=sharing
Lastly, what are your spectrogram parameters to generate the
waterfall?
I am using an FFT size of 2048 with a blackmanharris window of the
same size, and overlapping by 1024. My MATLAB command is:
spectrogram(slice, blackmanharris(2048), 1024, 2048, 50e6,
'centered');
I'll reach out again after I attempt to reproduce.
Sounds good. Let me know if you need any other data or
clarifications on what I am seeing.
Thanks,
Brian
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