rg-213 moisture
it is crap cheep nasty coax
use heliax and some plated connectors dress with self amalgamate tape
it is more likly the antenna has changed impedance or is affected by the moisture
some get better some get worse
becouse the Q changes with moisture level
quotiant of gain relative to humidity
much like tuning a guitar string
then moving the guitar to a damp room
it sounds off tune
but is this the room the moisture ??? or both
so when you move it back
its tuned again
but tune the guitar in the moist room and move it back
?? and
maybe better resonance is achived as your on the moisture side is better side ... tuning range
rg213 is ment for inside the building
it is sensative to uv and moisture as you have found out
heliax isnt ...
impedance is realy only a measure of resistance
and not at any given point in general
so at a "hot " spot
much like a guitar string with a knot in it
you can encourage harmonic content etc and funny parasitics
try it.//./
initinatiously this is quite a good way to get gain from the feeder
attached is a device to self tune a guitar i designed just now
you can build into it a micro for self retune etc
even retune on the fly
amazing how much it looks like the simantics of an atu
and wonderfull handy devices they are too