On May 11, 7:23*am, "Richard" wrote:
Has anyone ever bored a hole into the ground and dangled a radial or
counterpoise down it instead of burying a radial 6" horizontally under the
ground or stringing out a counterpoise?

RF currents needing to travel a lengthy path through the earth to
reach such a vertical buried wire would encounter high losses.

The function of buried radials is to provide a low loss return path
for the r-f conduction currents induced in the earth near a monopole,
which result from displacement currents generated by radiation from
the monopole. Almost all of these currents lie within a radius of 1/2
of a free-space wavelength (regardless of the monopole height).

So the most efficient collection of these ground currents means the
radials should extend about 1/2 of a free-space wavelength from the
base of the monopole -- so that the currents won't have to travel very
far through the lossy earth before they are "captured" by a radial
wire.

The electrical length of buried radials with respect to the reduced
v.p. in their environment has no real bearing on how effective the
radials are at reducing the r-f loss in the ground system.

The r-f loss present in the radial ground system doesn't affect the
shape of the relative field pattern generated by the monopole, or the
propagation of the fields launched by the monopole. But as that
ground system loss is in series with antenna current, it will affect
the radiation efficiency of the antenna system.

A benchmark, real-world study of this subject was made by Brown, Lewis
& Epstein of RCA Labs in 1937. It showed showed that 113 evenly-
spaced, buried radials each 0.412 free-space wavelengths long and used
with monopoles from ~70 to 90 degrees in height produced measured
surface-wave fields at 3/10 of a mile that were within 2% of those
generated by a perfect monopole with a zero-loss r-f ground, over a
zero-loss ground plane.

This corresponds to an antenna system efficiency of about 96%, or 960
watts radiated for 1,000 watts applied to the feedpoint. For a
monopole with a radiation resistance of 36 ohms this 96% efficiency
means that the r-f resistance in the ground system is about 1.5 ohms.
There wouldn't be much practical benefit gained by using more/longer
radials.

The BL&E tests were conducted in the sandy soil of New Jersey, where
earth conductivity is rather poor.

RF