Hi Steve!
I insulate ALL of my Yagi elements with Grade LE phenolic! My rationale
is simple: it works! I know... some towertalkians would prefer that I
turn my antenna farm into a science experiment, but I'm gonna stick with a
winner!
25 years ago I had a very bad experience with unintended resonance caused
by a 3 element 20 meter beam with all metal construction mounted 10 feet
above a 40 meter full size 3 element beam with all metal construction.
The 20 meter beam totally ruined the performance of the 40M beam because
the 3 element 20M beam on a 10 foot mast looked just like a top loaded
vertical and lots of driven element energy was coupled into the top-loaded
vertical! Insulated elements totally solved the problem, and I've used
insulated elements on nearly 100 Yagis I've built since!
I design my T-matched elements with K6STI's YO program, but the length of
the driven element must be extended aproximately five percent relative to
the length predicted by YO.
73!
Frank
W3LPL
donovanf@sgate.com
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