The reduction in efficiency is a direct result of the
reduction in radiation resistance due to the
sloping top hat wires. With lossless ground,
there is no reduction in efficiency.
I have an inverted L, with a 70' vertical section.
I was able to adjust the radiation resistance by
changing the height of the end of the horizontal
section. I adjusted the height by tying a rope
to the wire and throwing the rope over my tower's
guy wires. By sliding the rope up and down
the guy (which ran from 120' to ground level,
and about 100' from the vertical part of the
inverted L) I confirmed that the radiation
resistance changed a noticable amount. The
resonat point changed very little. I selected
25 ohms as a desirable impedance because it
made matching with paralleled 75 ohm 1/4 wave
coax so simple.
Terry Zivney, N4TZ/9
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