Bill,
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 aj@signalhound.com. I can send you some troubleshooting steps to try to help this.
I look forward to your response.
Regards,
Andrew
