"Owen Duffy" wrote
Whilst there are articles around about the performance of shallow
buried radials, I have not seen any that deal quantitatively with
radials laid on the ground, or pinned to the ground as you describe,
and the effects of those different installations on antenna
efficiency.
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Owen, you may be interested in Program RADIALS3.

Once radials are buried in the ground, just below soil surface, I
don't think depth of burial matters very much. But things happen very
fast when resting on the soil surface and conductor height is raised
only slightly.

Consider a single counterpoise wire. When resting on the soil surface
propagation velocity along the wire is about half of the free space
velocity. Propagation velocity increases fast as height increases.
When height is greater than length the VF is very nearly 1.

When resting on the ground there is an equivalent loss resistance
distributed along the wire due to the mutual impedance with the
ground. The input resistance at resonance is high. Q is very small.
But a lot depends on soil resistivity.

With increasing height the coupling with ground decreases and so does
the input resistance. When height is greater than length the input
resistance is due only to conductor loss resistance and resonant Q is
high.

Resonant frequency increases with height due to the increase in VF.
The increase in VF is due to decrease in capacitance to ground when
considered as a transmission line.

Changes in capacitance, VF, resonant frequency, and induced loss in
the ground, mostly occur in first few inches of height above ground
but cannot be neglected until height is roughly greater than length.
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Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
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