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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