With regard to perfect ground/saltwater verticals are affected much
more than horizontals. The pattern of a horizontal dipole over usual
soil and over saltwater isn't very different. Once you're up over a
quarter wavelength or so there's not much difference in ground loss.
Verticals are a different animal and one over saltwater will
potentially kick the snot out of a dipole.
BUT, you need to have perfectly conducting ground all througout the
Fresnel zone, which can sort of be thought as the region in space
where the far-field pattern of the antenna is developed. Anything in
the Fresnel zone is going to have some effect on the pattern.
I don't know what the usual definition of the "size of the Fresnel
zone" is, but it's BIG. Think several tens of wavelengths radially at
least.
So if you could coat the earth with copper 30 wavelengths out from
your vertical antenna in all directions, you'd have a killer signal
compared to just putting down a very good radial field. Of course,
the practicality of this is dubious, drop this into google: (I love
google calculator...)
((((c / (3.5 MHz)) * 30)^2) * Pi * (0.003 in) * (9 (g / cc)) * (US$
3.55)) / pound
For very, very low horizontal dipoles an excellent ground screen can
reduce ground loss, but you'd be better to spend your money getting
your horizontal antennas up high where the ground quality doesn't
matter much.
Dan
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