Tom,

You can go on line and find tables of coax lengths that aren't 
recommended for various bands.   Perhaps you have a total overall length 
that the system doesn't like.

I'm also wondering about the installation.  Perhaps changing the angle 
of the radiating wire will affect things.  I think you have the end at 
10 feet; maybe raising or lowering will give you a change in swr.

You also said that it is grounded to the 40 foot metal mast.   Is there 
another  ground wire  running down from the feed point to ground?  I'm 
not sure I would trust  the several joints in the mast to provide a good 
rf ground.

If there is a single ground rod at the base, maybe try  attaching some 
radial wires and just lay them on the ground.

I have seen the web site for this antenna, and with all due respect, 
think that the claim of 2:1 swr across 120 khz of the 160 band is a bit 
pie in the sky.  I know that for ground mounted verticals the worse the 
ground system, the wider the 2:1 swr band width.    As the ground is 
improved, antenna efficiency improves and the swr bandwidth shrinks.


Post a time and freq for 160 test, and I will try to be there.

73, Steve KW3A