> I'm not sure I'd go too far with the FCC map. At my QTH, which is shown
> as average, actual ground/earth varies within a hundred feet from deep
> old riverbottom loam to limestone with a thin covering of topsoil (or
> sometimes none). While I don't know how this affects electrical ground
> conditions, the difference must be fairly pronounced - and I am very
> glad my shunt fed tower is based in the old riverbed.
If you only use ground rods or depend on earth as a counterpoise, where you
place the antenna locally can matter.
With a reasonably good ground, most of the losses are in the Fresnel region
outside the area you can control. The result is a mean value of all the
variables combined, local soil under the antenna doesn't matter much.
Since Rick's Beverages are long and likely cross a big sample area of soil,
most likely they do a good job of averaging ground. Not that ground is all
that important for a Beverage.
Mostly what we find, when we cut through all the emotion, is we try to find
a way to justify why our locations and antennas are somehow "special". In
truth, the description of sorting multiple stations or having directivity in
the BCB being somehow exceptional, like a "long Yagi", is just common
performance.
I lived in NW Ohio in an area with deep rich sandy black loam with water
near the surface, and BC conductivity estimates from local AM station proof
of performances placed that soil above 20 mS/ meter for that whole area, but
nothing totally off the charts. The seriously flawed ground rod test using
60 Hz was off the charts for conductivity, because the top black soil layer
was saturated with contaminated water.
What we forget is skin depth can be many dozens of feet, and the wavelength
is so long we get an averaged effect of all the stuff going on. We look at
one tiny area near the surface, or look 1000 feet deep, and assume that
defines something one way or another, usually to unintentionally make a
system "special".
My Beverages over that good very uniform soil worked exactly as described
over rocky poor soil.
As a matter of fact, they worked the same in Cleveland over clay, and in
Rockdale County GA over rock. They work that way here, too.
I could always go to the AM band with any properly installed Beverage of
400-500 feet or longer and change directions, and sort multiple AM stations
on one frequency. It is common antenna behavior, because the "test" being
used is so non-critical.
It always fascinates people who listen, when several stations can be sorted
on one AM BCB channel. That a normal reaction to a common non-special result
where just 10 dB of response variation over nearly equal signal levels
arriving from widely separated directions shows up as "changing audio like a
switch".
It's human nature, just like we commonly see when antenna systems are
changed, and why we should make measurements. The best example of this
common very human effect is to change the battery in your car, clean it ,
and wax it. It will run better, and get better fuel mileage. (A popular Ham
author actually put that in an article on mobile installations!)
I think this is what Rick was driving at.
73 Tom
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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