Jim wrote:
i was surprised to find that the black plastic spiral cable wrap that i
was using as abrasion protection for a cb antenna shot my swr all to
hell! its heavy vinyl plastic but i thought that it would be rf
transparent! who can explain this?

Possibly changing the thickness of the cable (via the tape) changed its
RF velocity, which may change the SWR reading. Just a guess.

Making changes to RF cables after getting your SWR where you want it
can cause changes one wouldn't expect. I shot my SWR at the tx to hell
just by cutting a few extra feet of leadin out of the coax.