"Robert11" wrote
I realize that anything in the antenna feed loop degrades signals
top some extent, but how can (just) two BNC's degrade any to a
"meaningful" extent "

I can't tell you just how much attenuation a pair of BNC right
angles introduces, but I'd guess they'd add 1-2db. It isn't excessive
but I do know that they helped reduce some pager intermod that I was
getting, without harming the strong signals I wanted. Of course,
folding the antenna down so that it lay alongside the scanner case
blocked all but the strongest signals.
If you want to get the exact figures, look for specs on UG-306/U
or Amphenol 31-009.