[Antennas] antenna problem solving question

[KA4INM]

   Hi Bill W9OL:

/*snip*/
> coax is relatively new, maybe 4 years old with factory installed
> connectors from the amateur coax vendor here in Illinois.
> (forget the rg8 similar number at this moment)

> No big winds or lightning in the recent past.

> So where should I start looking? At the antenna's coax connection??
> Which is my first 'usual suspect'?

> please and thank you for you help in advance.

   I know this bites, but cut the problem in half first, disconnect the 
feedline from the "Sommer yagi" and substitute a test load. Re-test,
then you will know what you need to work on.
The feedline that twists around the rotator is most suspect.
-- 
   Ron  KA4INM - Youvan's corollary:
                 Every action results in unwanted side effects.