Is this real or a myth? I wondered and so asked Al K3LC. He studied the
question and had a good article about the topic. For 160m I use a 90 foot
irrigiation pipe vertical with four
wires in part of the top guys, each 42 feet long. The antenna looks
electrically like a quarter wave. So there is some improvement in the base
impedance, which helps make a matching network and antenna more efficient.
The main
question however was about the shielding or signal cancellation effect of
using such top loading. If I interpret his article correctly, the antenna
radiates equally well with or without such top loading. There is however a
big
benefit of using such top loading - much better bandwidth when that is used.
My results compare well on bandwidth with this data in his article. With two
matching L networks, each with two ceramic doorknob capacitors, I can
transmit anywhere in the 160m band with low swr. And it has helped me work 209
countries on 160m, which isn't too bad from Montana.
73 Bob W7LR _w7lr@aol.com_ (mailto:w7lr@aol.com)
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