Tom,
Great stuff! Could you elaborate on a couple of points -
1. I would think that a system with elevated radials that slope upward
towards the far ends (e.g for 160m 10' at feedpoint and 30' at far ends)
should have less loss as the field is less near earth where the voltage
is high in the radial. (unless there is something else that goes the
wrong way).
2. Is 1/4 wl resonance at all important as the number of elevated
radials increases - eg 10 total? The QEX N6LF papers seem to indicate
that a little less than 1/4 wl is optimum for that number of radials.
As much as I try to get answers to these from EZNEC+ the far field
results are all the same, 4 or 10 elevated radials and sloping or not,
resonant or not.
My VNWA shows my top loaded T for TB is "right on" but it doesn't seem
to work as well as I expected. Perhaps at N48 deg latitude (Redmond, WA)
one should not expect much for 160!
A "suffering seven" transplant,
Grant KZ1W
PS: if you have a moment please explain the pros and cons of skirt
wires. I think they are a good thing for top hat loading systems, but I
can't reason it out for elevated or in the ground radials. The old VLF
antennas all had them on the elevated ground planes, which isn't in any
current recommended practice.
On 3/2/2013 4:55 AM, Tom W8JI wrote:
Forgive me, please, if I'm re-hashing a bit of the "...same-old,
same-old" here, but I am really curious as to any "real world"
experiences that might be out there in the matter of elevated
radials, vs. those that are simply laid atop the ground...
(A) Is it true that a couple of elevated radials are just as
effective as the "optimum" amount of buried ones...?
Probably not a "couple", but almost certainly in small systems a few
elevated radials are better than the same number of buried radials.
Everyone would like this to be a "cookie cutter" answer, but the
actual results depend heavily on the soil and installation. Even N6LF
warns over and over that his data only applies for conditions like his.
(B) What is the "ideal" number of elevated radials that one should
use...?
As many as you can. More never hurts the signal, it just is more work.
(C) How many elevated radials are "just enough"...?
It depends on the soil, the height, the antenna, and what you want.
(D) How high should these radials be...?
It depends on the antenna, soil, and installation. Radial height takes
away from the effective antenna height. Certainly the safest thing is
about .05 WL , unless the antenna is really short and that takes away
significant radiator height.
(E) Would it be a requirement that I raise the feedpoints of my "L's"
to the same height as the elevated radials, or can I simply leave the
bases where they are now (at ground level) & simply slant the radials
upward with no effect upon performance...?
It probably doesn't make much difference.
(F) Is it OK to bend the elevated radials to fit property allotments...?
It depends on where they are bent. The best practice is straight and
symmetrical.
(G) What is the desirable length of an elevated radial...?
1/4 wave resonant length.
(H) Should any existing connections to real earth at the base of the
"L's" (i.e. a ground pipe) be completed severed with a system of
elevated radials...?
If the resonant radials are grounded to an earth ground, the system
will lose efficiency. This much is always the case.
Pick the particular story you like Eddy, that's what most people do.
:) Read the fine print though. N6LF, whose study is one of the most
comprehensive is a good source for that particular test condition.
Most people seem to miss this:
http://www.antennasbyn6lf.com/2012/02/elevated-radial-ground-systems-some-cautions.html
What he writes isn't often what people actually paraphrase.
73 Tom
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Topband Reflector
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Topband Reflector
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