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The recent discussion mentioning "conductive foam" reminded me of a serious potential problem to watch for. I had an old Gigatronics 600 series sweeper in which they had used pieces of conductive rubber foam wrapped around the outside of the microwave SMA connections, and held in place by tie wraps. It looked like the anti-static stuff used for storing ICs. I assume it was factory-done, for stopping any RF leakage - I wouldn't think that's a problem when properly torqued, but I guess they had their reasons.

Over the years, something in the foam - either sulfur compounds from vulcanizing, or acetic acid from latex - leached out and chemically attacked the SMA connectors to the point of mechanical failure. Trying to undo the SMAs caused them to break apart, ruining some of the modules. The gold-plated steel SMAs totally rotted out, while the stainless steel types survived externally, but their inner conductors were shot, and their threads gummed up so badly that some couldn't be umated without breaking. All of the lower frequency SMAs and SMBs that were not wrapped, looked brand new.

Ed

I have similar stuff in high-performance Mil stuff. The SMAs were all
overpainted with silver bearing paint, and the entire box was lined with
microwave absorbing black foam sheet.

This was in a 2 to 16 GHz Instantaneous Frequency Discriminator

-John

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