..J.S... wrote:
I am using a vertical dipole (Sigma 5) 1m above ground.
Will it make sense to try to improve the ground by digging in lots of wires
around the antenna ?




Regards/JS


Hi J.S.

Cebik says concerning the Inverted L antenna- which is similar to the
vertical Dipole that : "There is little evidence, despite the vertical
position of one arm of the antenna, that the inverted-L would benefit
from a ground plane beneath the antenna. The actual low-angle gain of
the inverted-L will, however, vary with the quality of the soil in the
region of reflection at a distance from the vertical arm. All patterns
were taken over average soil, and soils that are either poor or better
than average will tend to show a higher gain and lower take-off angle,
at least on the fundamental frequency."

You might do well to read his articles at : http://www.cebik.com/radio.html
He has quite a few dealing with the effects of different radial systems
for vertical antennas.

Food for thought and it might save you time and back breaking labor.

73 Dave

You might do well to read his (Cebik's) articles at :

http://www.cebik.com/radio.html

He has quite a few dealing with the effects of different radial systems
for vertical antennas.

Food for thought and it might save you time and back breaking labor.

73 Dave

===========================

Without any doubt, Cebik is the finest author on radio antennas. The extent
of coverage of practical subject matters, numerical accuracy and use of the
English language are beyond reproach.

How he manages to find time even to keep his web-site in good working order
is amazing.

But even for the above-average-intellect amateur, the amount of detail is
too excessive to take in. Few people have time available for a complete
study. And I'm an approaching, still willing to learn, octagonarian.

What is needed is a very much abbreviated summary, just the essentials of
his works. Perhaps in small book form. But this can be produced, without
unintentional distortion, only by Cebik himself. Does such a work exist?

=======================

I have searched without success for the behaviour of simple antennas in the
presence of so-called poor ground soils. Can't find much in Cebik except
doubtful, expensive computer programs.

The 'constants' of ground soils are Resistivity (Conductivity), Permittivity
and Permeabilty. (In the absence of magnetic material such as iron in the
soil permeability can be neglected.)

It is generally accepted that ground loss increases as resistivity increases
above that of salt sea water. But this cannot be universally true. Taking
the extreme case of soils which approach insulators (solid granite rock and
arid desert sands) it is obvious soil loss falls again to very low values.

There MUST be values of resistivity at which soil losses are at a maximum
but which reduce at higher values of resistivity.

Here we are concerned with buried ground radials. It is submitted that
maximum ground loss occurs at lower soil resistance values than are
upposed - if they are supposed or imagined at all!

Suppose soil resistivity is 377 ohm-metres, not a very high value, but it
happens to completely absorb, without reflection, radio waves received from
an antenna. Is this a suitable candidate for maximum loss in the ground?

The statement, for simplicity, ignores permittivity and the angle at which
radiation strikes the ground. But you get the idea.

Has anyone any info on this subject?

Of course, I may be trolling, just to catch old-wives. ;o)
----
Reg, G4FGQ

Reg Edwards wrote:
. . .
It is generally accepted that ground loss increases as resistivity increases
above that of salt sea water. But this cannot be universally true. Taking
the extreme case of soils which approach insulators (solid granite rock and
arid desert sands) it is obvious soil loss falls again to very low values.

There MUST be values of resistivity at which soil losses are at a maximum
but which reduce at higher values of resistivity.

Here we are concerned with buried ground radials. It is submitted that
maximum ground loss occurs at lower soil resistance values than are
upposed - if they are supposed or imagined at all!

Suppose soil resistivity is 377 ohm-metres, not a very high value, but it
happens to completely absorb, without reflection, radio waves received from
an antenna. Is this a suitable candidate for maximum loss in the ground?

The statement, for simplicity, ignores permittivity and the angle at which
radiation strikes the ground. But you get the idea.

Has anyone any info on this subject?

Of course, I may be trolling, just to catch old-wives. ;o)
----
Reg, G4FGQ

Go to groups.google.com and look up the thread "Just a comment on losses
in the ground", in mid-January 2002, in which we both participated. The
posting I made on Jan. 13, in particular, had a fair amount of
information on the topic, but other postings in the thread are worth
reading.

Roy Lewallen, W7EL

KC1DI wrote:


Cebik says concerning the Inverted L antenna- which is similar to the

vertical Dipole that : "There is little evidence, despite the
vertical
position of one arm of the antenna, that the inverted-L would benefit

from a ground plane beneath the antenna. The actual low-angle gain of

the inverted-L will, however, vary with the quality of the soil in
the
region of reflection at a distance from the vertical arm. All
patterns
were taken over average soil, and soils that are either poor or
better
than average will tend to show a higher gain and lower take-off
angle,
at least on the fundamental frequency."

You might do well to read his articles at :
http://www.cebik.com/radio.html
He has quite a few dealing with the effects of different radial
systems
for vertical antennas.

I'd have to look at the articles later...But, as it is, I would
have to disagree with that. An inv-L is nothing like a 1/2 wave
vertical. He may be referring to an extended version, but normally,
an inv -L is a single wire loaded, 1/4 wave vertical,
and relies on the ground connection.
Max current is still at the base, and you can lose a lot to ground,
if it's poor. A longer 3/8, etc L would show lesser losses, but
radials would still help some.
MK

Mark,

In the article quoted, Cebik was describing a half-wave "L" fed at the
corner; basically a bent half-wave dipole in an odd orientation.

He fully agrees that the more typical base-fed quarter-wave "L" would
benefit from radials.

73,
Gene
W4SZ

wrote:
KC1DI wrote:


Cebik says concerning the Inverted L antenna- which is similar to the


vertical Dipole that : "There is little evidence, despite the

vertical

position of one arm of the antenna, that the inverted-L would benefit


from a ground plane beneath the antenna. The actual low-angle gain of


the inverted-L will, however, vary with the quality of the soil in

the

region of reflection at a distance from the vertical arm. All

patterns

were taken over average soil, and soils that are either poor or

better

than average will tend to show a higher gain and lower take-off

angle,

at least on the fundamental frequency."

You might do well to read his articles at :

http://www.cebik.com/radio.html

He has quite a few dealing with the effects of different radial

systems

for vertical antennas.


I'd have to look at the articles later...But, as it is, I would
have to disagree with that. An inv-L is nothing like a 1/2 wave
vertical. He may be referring to an extended version, but normally,
an inv -L is a single wire loaded, 1/4 wave vertical,
and relies on the ground connection.
Max current is still at the base, and you can lose a lot to ground,
if it's poor. A longer 3/8, etc L would show lesser losses, but
radials would still help some.
MK