An interesting --- and very easy to overlook! --- reference in ON4UN's
latest lowband bible in the matter of ground radials...
Specifically, wire laid atop the ground may be considered to have a velocity
factor of 50%...which means, of course, that any 1/4-wave (physically long)
radials that I meticulously laid-out beneath my inverted "L" last year were,
in fact, 1/2-wave (electrically long) radials...
~73~ Eddy VE3CUI - VE3XZ
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Hi Eddy,
This is the first time I have had the temerity to chuck in my penny-worth on
the Topband reflector. (Too frightened of putting my foot in my mouth)!
I also hope I do not get into trouble for quoting directly from the latest
low band bible - I have added some brackets in the quote - but here goes:
".... If you use just a few on-the-ground radials over poor ground, the
radials may act like they are somewhat resonant. (The resonance vanishes if
you have many radials or if the ground is good to excellent). For these
cases it is best to use radials that are an electrical quarter-wave long.
............on 160 meters you should use 20-meter long radials if you are
only using a few (up to four). But that's bad practice anyhow: Four is far
too few radials. As soon as you use a larger number of equally spread
radials the resonance effect disappears, and the radials form a disk, which
becomes a screen with no resonance characteristics. In this case we no
longer talk about length of radials but about the diameter of a disk hiding
the lossy ground from the antenna."
The way I read this is that for the situation where you only have a handful
of radials you would then worry about having them an electrical quarter wave
for best effect. The primary aim of the ground radials is to collect the
return currents from the antenna. As the antenna is radiating in free space
then the larger the disk the better within reason. A quarter wave physical
radius disk being a good compromise size to aim for.
73
George, VK5ALS
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