The assumption that the skin depth varies inversely as the square root
of frequency is valid only for good conductors. Most types of soil fit
this category only at low frequencies, with the transition falling on or
near the HF range. For example, average soil (conductivity of 5 mS/m,
dielectric constant of 13) behaves like a conductor only below about 7
MHz. Above that, it's more like an insulator, where the skin depth stays
constant with frequency. Here are the skin depths in feet for average
soil at various frequencies:

0.25 MHz 47.6
0.5 MHz 34.2
1 MHz 25.0
2 MHz 19.0
4 MHz 15.4
7 MHz 13.8
10 MHz 13.2
100 MHz 12.6
1 GHz 12.6

There's a very good discussion of this in Kraus' _Electromagnetics_.

This doesn't alter Richard's conclusion that radials near the surface
make a much better ground than a single vertical conductor or
"connection" to ground.

Roy Lewallen, W7EL

Richard Harrison wrote:
Richard wrote:
"I have access to a 65 ft. water well that I could install a radial in."

A radio wave traveling along the surface of the earth has its electric
lines of force tilted slightly forward so that the direction of
propagation is slightly tilted downward. The earth is a poor conductor
as compared with copper. The earth absorbs and dissipates some of the
wave`s energy.

Skin effect is the phenomenon of high-frequency current concentration on
a conductor`s surface. Skin effect applies to earth as it applies to
copper, but the penetration depth depends on wavelength and resistivity
of the conductor. At 1 MHz, r-f penetrates copper to an effective depth
of only 0.0026 in.. The effective skin thiclkness (penetration depth) in
the earth depends on its dielectric constant. In ordinary soil the
dielectric constant may be 15 and may vary with moisture in the soil.
Water has a dielectric constant of about 80. Very dry soil may have a
dielectric constant of only 2 to 5. Soil conductivity varies from 1 mmho
to 40 mmhos.

At I MHz, the effective skin thickness of the earth, with good soil
conductivity of 36 mmhos per meter, is about 8.5 feet. At a soil
conductivity of 6 mmhos per meter it is 20 feet. For a poor conductivity
of 1 mmho per meter the skin thickness of the earth is about 50 feet at
1 MHz.

Sea water has a dielectric constant of 80, and has an effective skin
thickness at 1 MHz of 0.738 feet.

Skin effect thickness varies inversely with the square root of
frequency.

Point is that contact with the soil at a 65-foot well depth is not
important at h-f, as r-f current flow at h-f is mostly confined to the
surface of the earth. Skin effect will confine the r-f path from the
water surface at the bottom of the well to the surface of the well bore
back out of the well to the surface of the earth around the well, if the
r-f can be caused to go down the well at all. Highly conductive radials
at the surface are the key to an effective ground for h-f unless you are
lucky enough to be in close contact with water in the sea..

Best regards, Richard Harrison, KB5WZI