Bob,
You didn't mention the model or manufacturer of your tower. The
best installation involves a genuine tapered bottom section of the
type made to accommodate a ceramic base insulator. Usually when you
find one, you also get the mounting hardware and ball gap that
accompanies it. You have to construct a concrete pier so the
insulator is elevated. This keeps it up above water, snow, blowing
debris etc. You have to have four copper straps coming down from the
bottom of the insulator to the ground system so that the concrete does
not have voltage across it--only the insulator should. The tapered
or cylindrical insulator and tapered bottom section should seat into a
pin hole on the bottom hardware mount allowing the tower to rotate so
there is no twisting of the tower. Obviously you need to guy the
tower as it is not free standing and the guys must either be RF
transparent or be broken up with johnny ball insulators so they do not
distort the pattern.
If you want to employ a free standing tower, or if you cannot find a
bottom section or insulator or both, you can construct a tower and
skirt feed it. You line the tower with 3 or 4 hot wires on insulators
running up the sides with horizontal rings connecting them to each
other every 20 feet or so and a ring at the top and bottom. If the
tower is guyed you'll still need to break up the guys so they don't
distort the pattern. Either way a quarter wave vertical with 100+
quarter wave radials will be a great flame thrower.
There's no need to reinvent the wheel. You can find a lot of photos
on-line of broadcast tower bases. This page should give you some
ideas: http://www.amgroundsystems.com/projects_2013.html
73
Rob
K5UJ
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