We're getting wrapped around the axle here, fellas.
Several good points have been made...and for the sake
of sanity, I'd like to echo them.
1) Earth with good conductivity is better than earth with
poor conductivity. You can improve that conductivity by
installing copper radials under the antenna. If you can
afford it. Doesn't matter whether you connect to them;
current will be induced in the earth below the radial system.
2) The higher the elevated radial system is above ground,
the less it matters. Inverse square law applies here.
Get it up as high as you can, to reduce the directly induced
earth currents.
3) 2 radials does not a Vertical Ground Plane make. 4 sort
of works, but you lose low angle radiation between the radials.
With 8, having a radial every 22.5 degrees, a reasonably uniform
pattern starts to emerge.
4) First reflection. Here, the 'pseudo-Brewster Angle' comes
into play. In optics, the Brewster angle defines the angle of
incidence, below which light does NOT exit at the complementary
angle. This varies with the index of refraction of the optical
material. Similarly, in earth, there is a brewster angle effect
which is a function of the earth conductivity.
If you're ground mounted, do some ray tracing, and see where this
takes place, with respect to the base of your vertical. A 1/4
wavelength vertical has most of this within 1/4 wavelength of the
base. For a 5/8 wavelength array, or a stacked 'Franklin' array,
the radials will need to be as long as the vertical is high.
If the vertical is elevated, the first reflection is way the heck
out there, where you can't control the environment. This puts you
back where I said, at the outset--at the mercy of your earth.
There is NO REINFORCEMENT HERE. Losses below the Brewster angle
(i.e. at low vertical angles.) can easily exceed 30 or 40dB.
5) A brief comment on water. Quoting K2AV: "operation on a saltwater
beach, where the reinforcement at very low angles over the sea is
spectacular, with spectacular results."
Sea water provides really good conductivity, and consequently,
a really low Brewster angle. Down in the 2-3 degrees vicinity. The
"Reinforcement" means that rays which penetrate the water (earth) at or
above the Brewster angle are refracted backup and out, as opposed to
down into the earth.
Any language suggesting 'seawater gain', or 'reflection gain',
is imprecise, at best. It IS true that verticals work better over highly
conductive earth. But there ain't no gain there.
Do not for an instant think this is also true of a freshwater lake.
It isn't. (I'm thinking of a recent CQ article with a freshwater pond.)
6) Lightning ground is another matter. How long do you think #10
copper wire will last, with 1,000,000 amperes running through it?
It's a resistor. Femtoseconds. Maybe Picoseconds. You can't protect
against a direct hit.
Short of copper plating earth, what you do for lightning protection
will have little effect on antenna performance, and vice-versa.
And this is a good topic for another post. This rant has gone on
long enough. :)
N2EA
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