"Cecil Moore" wrote
It would appear that 1/2 wavelength
buried radials do NOT present a high impedance.

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Cec,

.. . . . as demonstrated by program RADIALS2

which treats radials as transmission lines. As they truly are.

The permittivity of soil surrounding buried radials is high. It is due
to the moisture content of the soil. Water has a high permittivity K
= about 80. If the moisture content is 20 percent then the
permittivity is roughly K = 16 plus a little bit for the dry content.

The poor, low conductance of the dielectric material, in conjunction
with wire inductance, also has an effect.

The soil is mainly, minute rock particles and a little air. Rock has
K = 4 or 5. Air = 1.

Velocity factor of any transmission line = 1 / Sqrt( Permittivity ).

In some circumstances, there may be no point in having radial lengths
longer than 1/10th or 1/12th of the free-space wavelength.

If the soil has any magnetic material in it then the velocity is even
lower. But it's a waste of time trying to tune buried radials by
sprinkling iron filings around your garden.

The attenuation along buried radials is usually so high that even
1/4-wave resonance doesn't show up. Impedance versus length at low HF
is a smooth curve approximately equal to Zo. But input impedance of a
set of radials is NOT equal to the impedance of the individual wires
all in parallel. They interact with each other. The Law of Diminishing
Returns applies.

In perfectly dry desert sand with a resistivity of 5,000 or 10,000
ohm-metres and K = 3, the 1/2-wave resonance may appear on an
impedance vs frequency curve. Program RADIALS2 shows this effect as
evidence of reasonable modelling accuracy.

This is a case of ground loss decreasing as soil resistivity increases
further. It appears attenuation is a maximum when soil resistivity
is around several hundred ohm-metres (377?). Which is quite a poor
soil.

(I once had a garden of sandy soil. Resistivity was 400 ohm-metres
even in wet weather. Eventually I moved house. SR fell to 70. On the
160m band 7 radials, each about 10 feet long, plus the cold water
pipe, were good enough with a 3/8 wave inverted -L. I never tried
B,L,E's 118 radials, 1 wavelength long.)

But in bone dry sand-desert soil, just rock mixed with air, at low HF
one would not use a system of radials under a 1/4-wave vertical. The
antenna could be a horizontal dipole lying on the ground. ;o)
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Regards from Reg, G4FGQ
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