hi !
for years i ran a shunt fed tower with a 6 el 20m yagi on top as a tx
antenna for 160. I made sure that the antenna was well connected to the
tower and nothing happened.
Instead of trying to find a material that is electrically suficient as
well as mechanical, i would simply change the feeding. I can see no
reason to decouple the top yagi structure from the tower. At the same
time this has hazards in lightning protection too.
The extra capacity formed by the Yagi on top enhances the radiators
efficiency even further ( if its not already at least a full quarter
wave high )
All of this said without knowing all the detail of the installation.
I´d go for a Gamma match , equalize potentials on the top, and be done
with it and have no worries about insulation etc.
73 de wolf df2py
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