From: [email protected] [mailto:[email protected]] On Behalf Of Ed Breya via groups.io
Sent: 23 March 2023 23:01
To: [email protected]
Subject: Re: [HP-Agilent-Keysight-equipment] low amplitude readings below 10MHz on a 8591E

?

I'd suggest that in any SA case where the response falls off greatly toward the low end, that you have a bad/intermittent connection in the RF cabling or parts. If anything goes bad and opens up, you lose the DC/LF content, while there's still enough capacitance in place (just due to proximity - that's all it takes) to carry the RF at the upper end. The basic amplitude versus frequency envelope you see is a high-pass filter of the residual capacitance against the 50 ohms system Z.

The badness can be anywhere, in any connection or component. The most likely though, tend to be mechanically related, like contacts inside connectors, and switches such as in RF relays and attenuators, for instance. Sometimes you can cure or at least diagnose "switch" type problems by exercising them lots of times through the possible states. A good strong input signal can help too, to clean contacts. You can use any signal that's well below the maxim input power rating - even a FG or DC, if your RF sources don't have enough juice. In the case of step attenuators especially, you may need plenty of power to effectively hit the deepest/furthest back pad sections.

The recent observation that it seemed to be working again for no particular reason, then failed again, but slightly differently, is highly indicative of a marginal contact of some sort. You can expect such variable results until you find the true cause. Good luck.

Ed