I believe the length of buried radials is not that critical (bigger/more =
better) and one size fits all bands. Within reason, subject to all the
normal caveats, etc.

But what about elevated radials? Does anyone know Hustler's recommendation
for elevated radials on their BTV series of verticals?

I suspect they want a pair of "tuned" radials on each band when elevated
because that is what I have always seen. I am curious what Hustler says and
what the group opines.

k4ia
Buck
Fredericksburg, VA

the more and the longer the better of course! the perfect situation is an
infinite perfectly conducting plane. failing that it is up to you to figure
out how much wire you can suspend and how long you can make it. keep in
mind that the highest current density for the return currents (and hence the
most chance for losses) is near the base of the vertical, so a good screen
in close is a good investment. under my 80m elevated 4-square i have one
elevated radial that is 1/4 wave, but then under it on the ground i have
150' of 4' wide 2x4 galvanized fence in a cross pattern (100' from the
center of the 4-square radially out under each vertical then a 50' piece at
90 degrees to that one under each vertical.). under my 160m raised inverted
L's i have 8 radials that are about 1/4 wave long. both of these work well,
though if i was being a perfectionist and thought i could keep more wire in
the air i would add more.

"K4ia" wrote in message
news:aAApe.28651$iU.5809@lakeread05...
I believe the length of buried radials is not that critical (bigger/more =
better) and one size fits all bands. Within reason, subject to all the
normal caveats, etc.

But what about elevated radials? Does anyone know Hustler's
recommendation
for elevated radials on their BTV series of verticals?

I suspect they want a pair of "tuned" radials on each band when elevated
because that is what I have always seen. I am curious what Hustler says
and
what the group opines.

k4ia
Buck
Fredericksburg, VA

Dave wrote:
"The more and longer the better of course!"

Increases cost and wind loading.

If the ground plane is high above the earth, it isn`t required to hide
the earth from the radiator to prevent displacement current flow loss in
the earth.

If I recall the story, George Brown, the inventor of the ground plane
antenna wanted to use only two opposing 1/4-wave radials in his antenna,
but was persuaded by the RCA marketing department to use four.

The extent of the ground plane affects the radiation pattern. See Figure
21-10 on page 720 of the 3rd edition of "Antennas" by Kraus.

The imnfinite ground plane (soild line) has its maximum radiation at
zero-degrees or toward the horizon. !/2-wave radials (dotted line)
produces a slight elevation above the horizontal, but there`s not much
difference in field strength at the angle if the ground plane is
infinite or has 1/2-wave radials.

If you were a medium wave broadcaster, you would want the infinite
ground plane. Brown, Lewis and Epstein at RCA determined the number of
ground radials needed for very high efficiency long ago.

Best regards, Richard Harrison, KB5WZI

Dave wrote:

[regarding elevated radials]

the more and the longer the better of course! . . .

No, that's not true. The efficiency of a vertical antenna with elevated
radials declines noticeably as radial length increases beyond quarter
wave resonance. With half wavelength radials, the efficiency can be very
poor, depending on soil conditions, the number of radials, and the
height. Decreasing the radial length to less than a quarter wavelength
doesn't generally hurt the efficiency much. I'd guess that the
efficiency would peak again at 3/4 wavelength, but I haven't checked.
It's easy to model with EZNEC or similar program, and you can get a fair
evaluation of a system with a few radials using the free demo version.

I should mention that the resonant length of radials is shorter when
close to the ground than it is in free space. This has to be considered
when choosing elevated radial length, particularly if the radials aren't
very high in terms of wavelength.

Roy Lewallen, W7EL

Buck wrote:
"But what about elevated radials?"

Just like 1/2 of an elevated center-fed dipole, the element length
should be 1/4 wavelength for resonance with the other element(s). The
open-circuit at the far end appears at the feedpoint as a low impedance.

Best regards, Richard Harrison, KB5WZI

Just to add a little to Richard's quite correct advice.

A single well-elevated 1/4-wave radial has a resistive input impedance
of very roughly 25 ohms. It is, in effect, a horizontal 1/4-wave
antenna and forms, with a 1/4-wave vertical, a bent half-wave dipole
which will radiate just as efficiently as a straight wholely vertical
dipole. The radiation pattern, of course, will be different.

With two or more equi-distributed radials the radiation pattern
changes again and the resistive impedance presented to the base of the
antenna reduces still further.

When the height of radials above ground is of the order of 1/10th of
their length the resonant length begins to decrease. So when the
radials are lying on the surface of the ground the propagation
velocity is about only half of the free space value. Consequently, to
maintain the 1/4-wave resonant length, their physical length should be
reduced.

On the other hand, when the radials are lying on the ground surface,
ground loss damps down resonance and dimensions are no longer very
critical. A collection of surface radials can be of various lengths.
They can be investigated/selected by using a hand-held antenna
analyser.

Shallow-buried radials, in average sorts of soils, are practically
non-resonant and their lengths can be reduced without detriment to
small fractions of the free-space wavelength.

The attenuation at HF along buried radials is quite high. There is not
much point in having radials longer than the distance at which very
little current is flowing in them.

For the behaviour of buried radials in various soils see program
RADIALS2 from website below.
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Regards from Reg, G4FGQ
For Free Radio Design Software go to
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