"Ian White GM3SEK" wrote

That was an administrative policy decision rather than a technical
one.
From the technical viewpoint, everybody agrees that 120*0.25wl is
more
than enough to override the local ground conditions under the tower
irrelevant.

====================================

- - - - and since soil resistivity decreases with increasing
frequency, and the impedance due to soil capacitance also decreases
with increasing frequency, everybody agrees that 1/8th wavelength or
less is more than long enough.

And if that isn't enough, the velocity of propagation along buried
wires is considerably slower than the free-space value. It depends on
moisture content and permittivity.

The attenuation due to skin effect and wire inductance along lossy
radial wires is rather high. There's negligible current flowing in
them at distances greater than 1/4-wavelength at their own velocity.
The wires may just as well not be there.

Finally, as the wires spread apart, at appreciable distance
practically all the remaining current flows in the soil because the
cross-sectional area of the soil is far greater than that of the wire.
The longitudinal impedance of the wire is greater than that of the
soil.

The foregoing applies to low and medium resistivity soils. In arid,
sandy, rocky, cactus-growing soils, with resistivities greater than
5,000 or 10,000 ohms-metres, buried wires have low attenuation, they
become resonant and develop standing waves. It is then a good idea to
consider changing from vertical antennas to horizontal dipoles.

The effects can be estimated by calculations on model radial systems.

It may have been noticed that ground loss is least at low and very
high resistivities. So there must be a maximum loss at some
resistivity. I wonder if maximum loss occurs around 377 ohm-metres
after taking the reflecting angle into account?

If B. L & E, made any errors, they made sure they erred on the safe
side regarding numbers.
----
Reg, G4FGQ