John ON4UN addresses this question in "Low Band DXing".
His advice was to avoid shunt fed elements in a driven vertical array.
If the elements are dedicated (ie. not a shunt fed tower) then it is really
very easy to end feed the elements (insulated from ground):
Use a 6" piece of Garolite, or other suitable FRP rod, machined to telescope
into the bottom section of aluminum tubing. Pour a small concrete pad
(perhaps 1ft cubed) base for each vertical element and during the concrete
"set" impress the FRP rod 2" deep into the center of the pad. A few days
later sleeve the FRP rod 2" into the bottom aluminum section and cross bolt
it in place. Thus there is a 2" gap between the element bottom and the
cement pad. One of the bolts can be used as a simple connector for the coax
center conductor. Place three ground rods around the circumference of the
concrete pad. Cadweld a circular piece of plumber's copper tubing to each
ground rod. Connect your feedline ground to one of the rods. Connect your
radials (60 to 120 recommended) to the copper circle. Now you have a simple
and cost effective base insulated element. If you ever take it down just
pull the FRP out of it's indentation in the concrete and the FRP goes with
you!
73, Scott W3TX
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