Topband: Grounding the ends of radials

[Richard Fry]

Elevated radial wires perform much differently than buried radial wires.

Elevated, horizontal radial wires having self-resonant 1/4 wavelength used 
as all, or part of an elevated counterpoise for a monopole, tee, or inverted 
L should NOT have a low-Z (direct) path to the earth at the operating 
frequency at either end of those horizontal conductors -- such as provided 
by wired connections using ground rods.

If so, then those elevated, horizontal conductors no longer will have the 
characteristics of opposing, end-fed 1/4-wave conductors -- which have about 
zero r-f current at the ends opposite their feedpoints and maximum r-f 
current at their feedpoints, and which produce the best radiation 
efficiencies from such antenna systems.

The reason for this is that the r-f current flowing in to and out of the 
ground plane from the end(s) of such grounded, elevated radials constitutes 
loss that otherwise would add to the fields radiated by that antenna system.
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Depending on their wavelengths, number, and geometry, buried radial wires 
concentric with the base of a monopole provide a relatively low loss path 
for r-f currents flowing in the earth within about 1/2 wavelength of the 
monopole (due to its near-field radiation into the ground plane) to flow 
between the r-f ground connection of the transmit system and the feedpoint 
of the monopole.

The lower the r-f losses in that path, the greater the radiation efficiency 
of that antenna system.

As shown by well-documented physical experiments going back to 1937 and many 
subsequent real-world tests and measurements also accepted by the FCC, a 
monopole of about 55-deg electrical height or more driven against a set of 
~120 buried horizontal radials at equal azimuth spacing and each having a 
free-space wavelength of about 90 degrees produces a peak inverse-distance 
groundwave field at 1 km that is within several percent of the maximum 
theoretical field possible for that applied power when radiated by a perfect 
monopole of such electrical heights when driven against a perfect ground 
plane.

R. Fry