Forums › BB Series Discussions › Odd behavior during phase noise measurements
- This topic has 3 replies, 2 voices, and was last updated 1 year, 10 months ago by Andrew.
billmax April 30, 2021 at 11:26 am
- This topic was modified 1 year, 11 months ago by billmax.
I made an initial phase noise measurement (screenshot.630) and then brought up the dialog box to add a title. While that dialog box was open, the phase noise dropped (screenshot.631). When I closed the dialog, the noise went back up. Using Panasonic CF-54 as the BB60C host.
Anybody seen anything like that?
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AndrewModeratorAndrew May 3, 2021 at 10:01 am
Your first screen shot (630) shows an uncal USB warning, which would indicate data loss over USB during the measurement. This would generally affect the measurement negatively as there would be discontinuities in the acquisition, increasing the phase noise. The fact that you had a good measurement (no USB warning) with the dialog open is interesting, but might be a coincidence. USB data loss is generally random. In theory, nothing is different about the measurement when the dialog is open.
This USB warning will appear in most measurement modes. Can you confirm that you are seeing this reliably in either sweep or phase noise mode? If yes, we will want to troubleshoot this. If yes, can you provide the make/model/CPU of your PC?
You can reply here, or directly to me at email@example.com. I can send you some troubleshooting steps to try to help this.
I look forward to your response.
billmax May 3, 2021 at 1:27 pm
- This reply was modified 1 year, 10 months ago by billmax.
It’s a Panasonic CF-54 with 2.4GHz i5 CPU. I’ve used this combo for a couple of years without issue, although I’ve never tried phase noise measurements with it until last week. I rarely see uncal USB.
Given your explanation, I think the uncal USB in that capture was likely due to me not using the 2nd (power) USB plug. I was out of ports in that test configuration and had to give up something. It didn’t dawn on me that could be the source of the problem.
Possibly with the dialog box open it is polling the instrument less often, so single port supply is sufficient?
I had repeated the sequence multiple times. The behavior was consistent in all aspects – uncal USB with higher noise, then no uncal errors and lower noise when dialog box was opened.
Andrew May 3, 2021 at 3:29 pm
- This reply was modified 1 year, 10 months ago by Andrew.
Very fascinating behavior. From the measurements point of view, nothing changes with the dialog active. Sweeps are still polled at the same speed, etc. The dialog being active could trigger other system behavior, maybe the system is giving increased CPU resources to our application with the dialog entry open, or something like that.
If you change the start freq from 10Hz to 100Hz or even 1kHz, does the USB error go away? The 10Hz start frequency requires a large continuous acquisition, and if your system was barely meeting USB throughput, that might push it over the edge.
Things that can affect USB throughput,
– Ensure your PC is set to “High Performance” power options. See the picture on my reply in this forum post. https://signalhound.com/support/forums/topic/vsg60a-stability-in-cw-mode-versus-multitone/
– Disable any anti-virus temporarily.
– If the BB60C is connected through a USB 3.0 hub, try removing the hub as a test.
– It sounds like your test setup is using another USB device. If that device is also a high USB usage device, that could be contributing to this.
– Keep your laptop on wall power.
In general I would not expect the auxillary power cable not being plugged in to result in data loss, but its possible. Does plugging it in resolve the issue? There is a separate low voltage warning you would see, and you might see sagging measurement values if power was an issue.
I look forward to your response.
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