I have a problem with many 8563E's and 64E's and 65E's where the signal level is not stable with any CW in Band 3 (12.5-26.5GHz), with a span of 10MHz and above. If you watch the display, you can see the signal at times dip on some units as much as 2db. The signal "bounces." I have noticed this on at least ten different spectrum analyzers. I've used multiple generators and cables so that is not my problem. It only happens in Band 3. All other frequencies and the signal is rock solid. A freq span below 10MHz in Band 3 also appears to make it rock solid. RBW setting has no effect. Has anyone ever experienced this? Does anyone have any idea what could be causing this problem?