Hi Doug,
One thing top-band operators using short antennas need to keep in
mind is if the capaciatnce at the top of a vertical (or end of a dipole)
is high compared to distributed capaciance in the structure, you
can put the inductor anywhere and efficiency will be virtually
unchanged. Efficiency, for a given ground system, would also be as
high as the ground system allows in a normal situation...and coil
design would be less critical.
Current in the radiator would be essentially uniform, making
radiation resistance about as high as is possible for a given height
antenna.
You could also ground the lower end of the coil and tap up on it to
find the 50 ohm point, and wind up with less loss than series feed
and an un-un.
I've used four "guy wires" as a capacitance hat and tuned some 30
foot verticals to self-resonace on 80 meters. I could then throw a
little inductance in at the bottom to work 160, and efficiency was
very high with a good radial system.
73, Tom W8JI
w8ji@contesting.com
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