"Capacitive coupling" is maximum near the voltage point of an
antenna. Moving the voltage near earth and concentrating it around
one single radial is generally not a good idea.
Ground losses are a combination of three effects. Radiation,
magnetic induction field, and electric induction field losses. The
only way to reduce losses to low levels is to move the antenna up
away from earth a large distance (more than 1/4 wl), or to cover the
earth with a screen or radial system of some form.
This is especially important near the antenna. To substantially
reduce losses, we have to spread the fields out over a larger cross-
section of earth.
The bulk of losses with any of these antennas are right around the
antenna, not ten miles or even several hundred feet away.
Even a very small limited space antenna like an inverted L will do
very well if some effort is put into the ground system. My friend
K8GIJ was always within a few dB of my signal (I used a 1/4 wl
vertical tower with 100 radials), and he only had a 15 foot deep and
100 foot long back yard! But then Harold filled his small yard with
radials, and even tied the fences and everything else in to his
ground system.
1/4 wl long is fine, and is probably the best overall length. There is
a little to be gained going longer, but as others have said you have
to be careful to NOT move maximum current into the flat top area.
You want maximum current in the center of the vertical section,
that maximizes current over the entire vertical area of the antenna.
73, Tom W8JI
W8JI@contesting.com
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