ARRL Extra Class License Manual, Page 9-8 Effects of Ground and Ground
"There is little you can do to improve the far-field, low-angle
radiation pattern of a vertically polarized antenna if the ground under
the antenna has poor conductivity, the most important factor affecting
ground losses. Most measures that people might try will only be applied
close to the antenna and will only affect the near-field pattern. For
example, you can add water to the ground under the antenna, but unless
you watered the ground for 100 of more wavelengths, it wouldn't improve
the ground conductivity for these distant ground reflections. Adding
more radials or extending the radials more than a quarter wavelength
wont help either, unless you are able to build an extensive ground
screen under the antenna out to 10 or more wavelengths!"
Need I go on?
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