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Agilent 8720 C Network Analyzer Internal Issues

Question asked by jdiplexers on Jul 31, 2013
Latest reply on Aug 3, 2013 by drkirkby
I have an interesting issue with an 8720C Network Analyzer and was wondering if anyone had seen it before, know what the issue is, and hopefully a way to fix it or an outfit that you would recommend to fix it for me.

I was testing some filters for a customer and noticed some strange rippling occurring at the passband region so I began to investigate my calibration and the analyzer and finally noticed the issue. As you can see in the first picture below, the noise floor for the S21 port has an abnormal spike at close to 8 Ghz with a calibration correction on. The noise is always there after the calibration and vanishes when the correction is turned off (see second attachment). I seem to be getting an some em influence inside the analyzer at some point, causing my calibration to give an erroneous spike around 8Ghz.  I verified the calibration equipment was good and port 2 does not have any of the same issues I saw in port 1.

I turned on another analyzer that we had in the side of the lab to see what issue it had and it has the exact same problem. Has anyone run into this problem before?