RadioBanter - Radials for a Vertical ?

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Thanks for the input. I will check out the QEX article.

The fence is block and my "neighbor's yard" is a horse exercise pasture.
The horse farm behind me breeds and trains race horses.

Mark, KJ7BS

"'Doc" wrote in message
m...
Mark,
Good question! There will be ~some~ gain/loss of signal in
various directions. Probably won't be much gain or loss,
just depends on 'other' things (how near the fence, fence made
of wood/metal, and other mysterious things). Wouldn't worry
too much about it, and if it really bothers you, sneak a radial
or two under the fence for a ways. Hide it well and don't get
caught running stuff in your neighbor's yard!
'Doc

Mark wrote:
Thanks for the input. I will check out the QEX article.

The fence is block and my "neighbor's yard" is a horse exercise
pasture. The horse farm behind me breeds and trains race horses.

A friend has just buried a large amount of chicken-wire under the
surface of his wife's new horse-schooling area, so it can double as his
antenna testing range.

You might at least be able to persuade your neighbor to let you slot in
a few radials with a spade.

--
73 from Ian G/GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

I have read Al Christman's QEX article, and though he mentions radial systems
used in AM BC stations, I doubt if he's read Brown, Lewis and Epstein, else I
also doubt if he would have made some of the statements that appear in the
article

The Brown, Lewis and Epstein paper is a must read for anyone contemplating the
installation of radials for a vertical radiator. Fortunately, Richard Harrison
has supplied the paper in the thread below 'Brown Lewis and Epstein'.

My post below has also been added to the above mentioned thread. However, I
apologize for the problem in making the tabular data come out right--I tried,
but was unsuccessful, so I hope you can interpret the data to be useful to you.
Now to the mail I posted in the above mentioned thread. Walt,W2DU

Thanks to Richard Harrison, he has supplied us with the renowned Brown, Lewis
and Epstein paper, reporting the voluminous and enlightening experimental data
concerning the length and number of ground radials required in approaching the
condition of perfect ground underneath a vertical radiator. This paper has long
been well known and highly respected in the communications engineering
community, and since 1938 has become the standard for engineering the radial
systems for AM BC stations Worldwide. The FCC requirement for radials in US BC
stations is based on data in the BLE paper.

The tragedy here is that BLE paper has gone practically unknown in the amateur
community, as witnessed by so many continual questions and incorrect answers
concerning the length and number of radials required to achieve the desired
performance of our vertical radiators.

So let me present a short, but definitive abstract of the pertinent numbers
taken from the paper, that answer some of the pertinent questions correctly.

As a reference on which to base the radiated field strength, the industry
standard has traditionally used millivolts per meter to describe field strength.
Specifically, the field strength of 194.5 millivolts per meter at one mile,
radiated from a quarter-wavelength radiator over perfect ground with 1000 watts
input, is the industry standard. In other words, this field strength is the
maximum attainable under ideal conditions. The data below, obtained directly
from measurements made at 3 MHz by Brown, Lewis and Epstein in 1937, provide
definitive answers to those who ask how many radials of what length are
necessary to provide a suitable ground plane. When comparing the fields
strengths below, remember that 194.5 mv/meter is the field strength obtained
with perfect lossless ground.

Number of Field Strength Loss in dB Relative

Radials in mv/meter to Perfect Ground

Length Length

0.4 wl 1/4 wl 1/8 wl 0.4 wl 1/4 wl 1/8 wl

113 192 180 152 0.112 0.673 2.14

60 185 176 150 0.435 0.868 2.26

30 174 162 150 0.967 1.59 2.26

15 158 153 1.81 2.08

2 126 120 118 3.77 4.19 4.39

When reviewing these data, please keep in mind that as the field strength
approaches 194.5 mv/meter the effective ground is approaching perfect ground,
which means that the conductivity of the ground in which the radials are planted
is irrelevant, only the ground external to the radial system is relevant with
respect to conductivity.

It should also be kept in mind that the energy in the EM fields surrounding the
vertical radiator diminishes with distance from the radiator. Thus the
displacement currents entering the ground diminish proportionately with
distance. Consequently, there is a distance from the radiator after which the
currents become too small to be significant to the conservation of power
radiated. This fact determines the maximum length of the radials necessary to
reach the point where the law of diminishing returns prevails. The measurements
reported in the BLE paper show this distance to be between 0.4 and 0.5
wavelengths. As noted above, this distance is relative to the amount of energy
in the displacement currents at this distance from the radiator, and is in no
way relevant to any resonant length of the radial. It is well known that radials
buried in the ground lose all sense of resonance.

Walt, W2DU

Man, O, Man, do I have some apologizing to do to Danny Richardson, K6JHE. Danny
is the one who supplied the data on the Brown, Lewis and Epstein paper, not
Richard Harrison.

I'm sorry, Danny, it was a senior moment at age 86 that's responsible.

Walt, W2DU

"Walter Maxwell" wrote in message
...
Man, O, Man, do I have some apologizing to do to Danny Richardson, K6JHE.
Danny is the one who supplied the data on the Brown, Lewis and Epstein paper,
not Richard Harrison.

I'm sorry, Danny, it was a senior moment at age 86 that's responsible.

Walt, W2DU
Dang, I can't seem to get anything right today. Can't even spell Danny's call
sign correctly. Repeat after me, it's K6MHE, it's K6MHE, it's K6MHE.

Walt, W2DU

I only wish I had contributed B, L, and E`s findings on antenna radials.
My information has always come 2nd hand from its reprinting by Ed Laport
in "Radio Antenna Engineering. Ed has formulas to use in choosing your
ground system. I can`t find my copy of Ed`s excellent book at the
moment. Laport, like Walter, W2DU, is an RCA alumnus and has associated
with the famous pioneers. K6JHE did us a favor by posting the original
data.

Common sense says that earth closest to a vertical tower gets most of
the capacitive current between the tower and the earth. It is important
that density of the ground radials be high close to the tower to reduce
current in the lossy soil.

I think there is more to it.

The area of a circle around a tower is (pi)(r)(r), where r=distance from
the tower. Area grows as the square of the distance from the tower.
Assume a unit depth for the earth crust, and cross-section becomes equal
to the surface area.

The resistance of a conductor is its resistive coefficient times its
length divided by its cross-sectional area.

Total resistance seen by a ground wave traveling away from a tower is an
inverse function of the distance from the tower`s highly conducting
ground system. The farther from the tower you get, the more
cross-aection there is, so the less resistance there is in the earth.
This must be in textbooks, but I don`t recall seeing it. I once asked
what a-c resistance to use for the earth at 60 Hz, 50 some years ago, in
a student problem and was told to use 25 ohms, no matter what the
distance through earth was. That`s when I noodled out the above
explanation for the earth`s resistance. It should work at r-f too except
for skin effect which if I recall causes an increase in resistance
proportional to the square root of the frequency. The skin thickness is
proportional to the reciprocal of the square root of the frequency.

The point is that high conductivity is only needed very close to the
tower for the ground wave. For a sky wave, you need high conductivity at
the reflection point for a vertically polarized wave.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
. . .
It should work at r-f too except
for skin effect which if I recall causes an increase in resistance
proportional to the square root of the frequency. The skin thickness is
proportional to the reciprocal of the square root of the frequency. . .

That's an approximation which is true only for a good conductor. A poor
conductor like ground acts like a conductor only up to a particular
frequency, above which it acts like a dielectric in which the skin depth
stays constant with frequency. Of course, there isn't an abrupt change,
but the characteristic transitions from one to the other much like the
frequency response of a highpass filter transitions from a fixed rising
characteristic to flatten at the break frequency.
Here are the transition frequencies for some common types of ground,
where the first number in parentheses is the conductivity in S/m, the
second is the relative permittivity (dielectric constant):

Very good (0.0303, 20): 27.2 MHz
Average (0.005, 13): 6.9 MHz
Poor (0.002, 13): 2.8 MHz

For many purposes involving electromagnetics including determining skin
depth, the ground acts like a conductor below the transition frequency
and like a dielectric above it.

For example, here's the skin depth in feet for average soil at various
frequencies:

Freq MHz Skin Depth Ft

0.5 34.2
1 25.1
3.5 15.9
7 13.8
10 13.2
30 12.6
100 12.6

A very good treatment of this can be found in Kraus' _Electromagnetics_.

Roy Lewallen, W7EL

Dear Richard:

Your last paragraph (quoted below) is a good summary. It, or something
like it, should be an introductory paragraph in every vertical's data sheet
and advertisement. Well done.

To have a vertical perform well for the important (for DX) angles
between 2 and 12 degrees (above the horizon) one would like to have a copper
sea starting one or two wavelengths from the antenna. I have worked 10 watt
backpack stations in the UK when they were by the sea side. No hope to do
so when they are inland.

73, Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Richard Harrison" wrote in
snip

The point is that high conductivity is only needed very close to the
tower for the ground wave. For a sky wave, you need high conductivity at
the reflection point for a vertically polarized wave.

Best regards, Richard Harrison, KB5WZI

I have worked 10 watt
backpack stations in the UK when they were by the sea side. No hope to
do
so when they are inland.

Three or four weeks ago I drove down to the beach to do
some fishing, bbqing, and general r&r. Of course, I had my
radio. I pulled my truck right up next to the water. Didn't
bother throwing a "water" ground wire out. Just ran normal
with my "extended" 14 ft mobile whip. The coil 8 ft above the
base of the whip. 100w. Was yakking on 40m late at night, and among
all the stations, mostly home stations, some running power,
I was one of the loudest ones on the freq. Can't beat a good
sal****er location. :) Also, a mobile late at night on 40m,
generally is as good as most normal height dipoles, etc. In fact,
I had one guy do a test. He was in the house in FLA, and I wagered
that his signal would increase if he went to his mobile.
He did, and it did. MK