Everybody acknowledges that a good ground is required for any amateur
work, especially for a vertical. When I'm putting in an RF ground for
either my station or for an antenna system, how do I know when I've
achieved "good enough"? What works?
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Anything will work!
To summarise, begining with 1 radial, all you can do is keep laying more
radials until performance ceases to improve. Then that's the best which can
be done at your QTH. Performance can be judged by measuring the strength of
fixed, stable, not too distant, MF and lower frequency HF radio stations in
daylight. There's an effect known as "Reciprocity" which means that an
antenna with its ground system is just as good or bad on transmit as it is
on receive.
If you increase the number of shallow-buried radials by 50 percent and
there's no noticeable improvement then stop laying. Depending on the type of
soil you will end up with a number which, in general, will be fewer than
what you thought of before you started.
With a vertical, much depends on the lowest frequency of interest. Opinions
differ but in my opinion, in average garden soil, there's not much point in
laying shallow buried radials longer than 1/10th of a wavelength. They can
be shorter in very fertile, fine, damp soil and longer in dry sandy or rocky
soil. Fertility is the key. Increase their number according to the above 50
percent guidline.
Layout and bends in the wires are unimportant as are varying lengths. Just
spread them out fairly uniformly over the area available. A 180-degree
missing sector because the house gets in the way is not of great
consequence.
Wire diameter has little electrical effect. Choose wire diameter according
to type of soil and wire durability.
Forget about ground rods. A ground rod is little better electrically than a
horizontal radial of about the same length. A short ground rod can be used
as a common connecting point.
If you like amusing yourself with numbers, and for crude predictions of what
to expect, download programs EARTHRES and RADIALS2 from website below. A
little knowledge of your local soil resistivity can add much to the interest
and help you to forget the lumbago.
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Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
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