On Wed, 27 Apr 2005 20:15:03 -0400, Mike Coslo
wrote:

The main reason I ask though, is that I thought I heard here some time
ago, that a dipole would perform better over a good ground system.

Hi Mike,

You heard correctly. The ground system lowers losses which translate
to more power out. This is not method of controlling TOA, simply loss
- all angles of radiation improve.

I don't have the results published, but I have a near field study
showing interesting results for a dipole over ground, and over
shielded ground at:
http://home.comcast.net/~kb7qhc/ante...pole/index.htm

73's
Richard Clark, KB7QHC

"Richard Clark" wrote
The main reason I ask though, is that I thought I heard here some time
ago, that a dipole would perform better over a good ground system.

Hi Mike,

You heard correctly. The ground system lowers losses which translate
to more power out. This is not method of controlling TOA, simply loss
- all angles of radiation improve.
_________________

Note that the intrinsic, free space pattern/gain of a dipole does not depend
in any way on the presence or nature of a ground plane.

Reflections from the ground (and other objects) can modify the classic donut
shape of the dipole pattern and produce relative gain in some directions, at
the expense of gain in other directions. But the "power out," or absorbed
by a matched dipole will be the same in any case.

A low-resistance ground system will increase the fields radiated from an
antenna that uses the earth as an 'image' part of the complete radiation
system, such as the vertical mast radiators used in MW broadcasting. With a
perfect ground in this situation, the base current in the vertical mast is
twice what it would be for the same power applied to an equivalent wire
dipole (less a ground system) in free space -- resulting in 3 dB system
gain.

RF

Richard Fry wrote:
"With a perfect ground in this situation (MW vertical tower) the base
current in the vertical mast is twice what it would be for the same
power applied to an equivalent wire dipole (less a ground system) in
free space -- resulting in 3 dB system gain."

I`m not agreeing or disagreeing, just listing facts.

Arnold B. Bailey in "TV and Other Receiving Antennas"on p. 500 gives the
gain of a horizontal half wave wire (thin), center-fed as zero dB at its
center frequency. He should. It is his reference for all other antennas.
His authority is the famous G.H. Brown in Proc. I.R.E., Vol. 33, p. 257,
April 1945. Antenna resistance = 60 ohms.

On page 538, Bailey gives the free-apsce gain of the quarter-wave
vertical antenna. It too has a gain of zero dB = 0 dBd. His authority is
A.S. Meier & W.P. Summers in Proc. I.R.E., Vol. 37, p. 609, June 1949.
Antenna resistance 28 ohms.

Power is current squared times the resistance..

Terman says on page 886 of his 1955 edition:
"Effect of Ground on Directive Gain of Ungrounded Antennas. Consider an
antenna is far enough from ground so that the total power radiated by a
given set of antenna currents is independent of the presence or absence
of the ground. Then a ground reflection that reinforces the main lobe
will double the field strength of the main lobe, and so will increase
the directive gain of the antenna system by a factor of 4." (thet`s a
power ratio of 4)

On page 885 Terman says:
" Consequentially (due to ground reflection nulls), to obtain strong
radiation in the directions approaching the horizontal using a
horizontally polarized radiating system, it is necessary that the height
of the antenna above the earth be of the order of one wavelength or
more."

Also on page 885 Terman says:
"In the case of horizontal polarization the effect of imperfect ground
is seen to be quite small, especially at low vertical angles. With
vertical polarization the ground imperfections have greater effect; in
particular, the filling of the nulls at moderately low vertical angles
is very pronounced."

For the power to be the same in a vertical mast and a wire dipole, the I
squared R must be the same in both cases.

Best regards, Richard Harrison, KB5WZI

I wrote:
"With a perfect ground in this situation (MW vertical tower) the base
current in the vertical mast is twice what it would be for the same
power applied to an equivalent wire dipole (less a ground system) in
free space -- resulting in 3 dB system gain."
to which Richard Harrison responded.
____________

Excuse my inaccurate statement about that current, and thanks for catching
it.

The input resistance of a 1/4-wave monopole working against a perfect ground
plane is 36.5 ohms,* or half that of a 1/2-wave dipole in free space. A
given input power then results in 1.414X more current in the monopole than
the dipole. Hence the monopole radiates 1.414X the field of the dipole.
And, as shown in Kraus 3rd edition, Table 6-2, a 1/4-wave monopole against a
perfect ground has 3 dB more gain than a 1/2-wave dipole in free space.

Increasing the field from the 1/2-wave, free space dipole by 1.414X in the
above example would require doubling its input power (3dB), which would
result in the same 1.414X increase in its current -- to the same value as
seen in the monopole with 1/2 that power.

* per Kraus 3rd Edition, p 567

RF

This is unfortunately an example of arriving at the right result by
using the wrong (actually, incomplete) method.

The field from a conductor is proportional not only to the current
flowing in it, but also the length of the conductor. So if you put the
same current into a dipole and monopole, and assuming they have the same
current distribution, the field from the dipole will be twice the field
from the monopole.

So let's start again. The input R of a monopole over an infinite perfect
ground is 1/2 the resistance of a free space dipole, so for a given
power input the monopole current is 1.414 times the dipole current, as
you said. Ok so far. But because the dipole is twice as long and with
the same current distribution (and oriented in such a way that the
fields from the two halves add in phase), the field from the dipole is
2/1.414 = 1.414 times the field from the monopole. However, each ray
from the monopole is reflected from ground, resulting in two rays adding
in phase at a distant point. This doubles the field from the monopole,
so it's now 2/1.414 = 1.414 times the field from the free space dipole.
This is the same result, but with the two additional important factors
of radiator length and ground reflection included.

A good check of the final result is to note that, neglecting loss, the
average field intensity from *any* antenna in free space has to be 3 dB
less than the average field intensity from *any* antenna over an
infinite ground plane, if the same power is applied to each. The reason
is simply that the supplied power is spread over half the volume when
the ground plane is present.

Roy Lewallen, W7EL

Richard Fry wrote:
. . .
The input resistance of a 1/4-wave monopole working against a perfect
ground plane is 36.5 ohms,* or half that of a 1/2-wave dipole in free
space. A given input power then results in 1.414X more current in the
monopole than the dipole. Hence the monopole radiates 1.414X the field
of the dipole. And, as shown in Kraus 3rd edition, Table 6-2, a 1/4-wave
monopole against a perfect ground has 3 dB more gain than a 1/2-wave
dipole in free space.

Increasing the field from the 1/2-wave, free space dipole by 1.414X in
the above example would require doubling its input power (3dB), which
would result in the same 1.414X increase in its current -- to the same
value as seen in the monopole with 1/2 that power.

* per Kraus 3rd Edition, p 567

RF

Richard Clark wrote:

On Wed, 27 Apr 2005 20:15:03 -0400, Mike Coslo
wrote:


The main reason I ask though, is that I thought I heard here some time
ago, that a dipole would perform better over a good ground system.


Hi Mike,

You heard correctly. The ground system lowers losses which translate
to more power out. This is not method of controlling TOA, simply loss
- all angles of radiation improve.

I don't have the results published, but I have a near field study
showing interesting results for a dipole over ground, and over
shielded ground at:

Interesting indeed!

- Mike KB3EIA -

You heard correctly. The ground system lowers losses which
translate
to more power out. This is not method of controlling TOA, simply
loss
- all angles of radiation improve.

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

Some buried wires under a horizontal dipole, at a height of 1/4 or 1/2
wavelengths, will, in theory, reduce losses. Some old wife, once upon
a time, must have read something about it in a book without bothering
about the magnitude of the effect.

It's not enough to be detectable. So don't listen to your voices or
waste time digging up your back yard and getting back ache.

There's far too much of old wives reading things in books and
ill-written radio magazines, getting the wrong ideas, and then
plagiarising them. Which innocent people hear about 3rd or 4th hand
or n'th hand.

The fabled SWR meter is another example.
----
Reg.

On Sun, 1 May 2005 23:06:25 +0000 (UTC), "Reg Edwards"
wrote:

Some buried wires

Some?

under a horizontal dipole, at a height of 1/4 or 1/2
wavelengths,

Why that high? Another Wives' tale? What about 1/8 or 5/8 (or even
some fraction in between)?

will, in theory

Whose theory?

, reduce losses.

Clearly loose conjecture. You got any data, or is this merely
rustling baking crumbs out of your apron?

73's
Richard Clark, KB7QHC

Richard, I can see you adopt the same attitude as I do towards
questions on this newsgroup which begin with "I have heard that . . .
.. ".

Hardly a reliable start to a question. One gets the impression the
questioner is unlikely to be able to understand the answer and tailors
the answer to suit.

Looking back over my career, I have never(?) taken anything out of a
book (Terman, etc) at face value. The number of occasions on which
errors and uncertainties of one sort or another have come to light has
justified the time and effort expended in checking.

Anybody who quotes Terman as from a Bible has only ever read him but
must have never actually used him in anger. I mention Terman only as
an example but hasten to add, in my opinion, he is amongst the most
reliable of popular technical authors. I have only his first edition
produced in the middle of WW2.

The work which continued during the life and death struggles between
the nations of WW2 never ceases to amazes me. During the battles of
Leningrad and Stalingrad, Russian engineers were designing High
Voltage DC power lines from yet-to-be-built hydro-electric power
stations deep in Asia, into Europe.

Stalin himself was concerned with the nutrition and the future of
school children. During the horrible prolonged battle of Stalingrad he
directed that children and mothers, then living in the frozen sewers
beneath the ruins, should be given top priority with food rationing.
This was based on the grounds that the average life of a soldier in
the city, having just survived crossing the river Volga, was only 7
hours and consequently he would not have time to eat and fully digest
a good meal.

As is well known the Germans ran out of food and ammunition first and
the survivors crawled out of the sewers and burning buildings to
surrender. The German generals must have known then the war was lost.
But it was not until 6 months later, in the Battle of Machines around
the city of Kursk, on the broad summer grasslands of the surrounding
steppes, littered with thousands of burning tanks, wrecked mobile guns
and aircraft, and deserted troop carriers, that Hitler must have been
convinced of ultimate defeat.

But another two years were to elapse and millions of Russian, Polish
and German lives were still to be lost before Russian tanks crossed
the Oder and Russian rockets and shells began to rain down on Berlin.
----
Reg, G4FGQ.

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

"Richard Clark" wrote in message
...
On Sun, 1 May 2005 23:06:25 +0000 (UTC), "Reg Edwards"
wrote:

Some buried wires

Some?

under a horizontal dipole, at a height of 1/4 or 1/2
wavelengths,

Why that high? Another Wives' tale? What about 1/8 or 5/8 (or even
some fraction in between)?

will, in theory

Whose theory?

, reduce losses.

Clearly loose conjecture. You got any data, or is this merely
rustling baking crumbs out of your apron?

73's
Richard Clark, KB7QHC

Reg:

I can see how one such as I might be confusing.
I came from academic institutions which (stated) they believed, "There are
no "dumb" questions, only "dumb" people who WILL NOT put these questions
forward."

I interpreted this to say, "You can either choose to look STUPID with your
question--and change, or, you can choose to maintain your pride (remain
silent) and remain "STUPID!"
I would like to think I choose the first (but, due to my limited resources,
has only marginally improved my stupidity)...

Also, it was common belief that a person had to hear the concept, idea, etc.
six-times before it was absorbed by the mind in question and became
"knowledge."
There may be those gifted in absorbing information on the first try,
however, I fall into the group I mentioned above. frown
It does make me appreciate men/women/children with tollerance and
patience--if that is any factor which would redeem me....

Warmest regards,
John

"Reg Edwards" wrote in message
...
|
| Richard, I can see you adopt the same attitude as I do towards
| questions on this newsgroup which begin with "I have heard that . . .
| . ".
|
| Hardly a reliable start to a question. One gets the impression the
| questioner is unlikely to be able to understand the answer and tailors
| the answer to suit.
|
| Looking back over my career, I have never(?) taken anything out of a
| book (Terman, etc) at face value. The number of occasions on which
| errors and uncertainties of one sort or another have come to light has
| justified the time and effort expended in checking.
|
| Anybody who quotes Terman as from a Bible has only ever read him but
| must have never actually used him in anger. I mention Terman only as
| an example but hasten to add, in my opinion, he is amongst the most
| reliable of popular technical authors. I have only his first edition
| produced in the middle of WW2.
|
| The work which continued during the life and death struggles between
| the nations of WW2 never ceases to amazes me. During the battles of
| Leningrad and Stalingrad, Russian engineers were designing High
| Voltage DC power lines from yet-to-be-built hydro-electric power
| stations deep in Asia, into Europe.
|
| Stalin himself was concerned with the nutrition and the future of
| school children. During the horrible prolonged battle of Stalingrad he
| directed that children and mothers, then living in the frozen sewers
| beneath the ruins, should be given top priority with food rationing.
| This was based on the grounds that the average life of a soldier in
| the city, having just survived crossing the river Volga, was only 7
| hours and consequently he would not have time to eat and fully digest
| a good meal.
|
| As is well known the Germans ran out of food and ammunition first and
| the survivors crawled out of the sewers and burning buildings to
| surrender. The German generals must have known then the war was lost.
| But it was not until 6 months later, in the Battle of Machines around
| the city of Kursk, on the broad summer grasslands of the surrounding
| steppes, littered with thousands of burning tanks, wrecked mobile guns
| and aircraft, and deserted troop carriers, that Hitler must have been
| convinced of ultimate defeat.
|
| But another two years were to elapse and millions of Russian, Polish
| and German lives were still to be lost before Russian tanks crossed
| the Oder and Russian rockets and shells began to rain down on Berlin.
| ----
| Reg, G4FGQ.
|
| =======================================
|
| "Richard Clark" wrote in message
| ...
| On Sun, 1 May 2005 23:06:25 +0000 (UTC), "Reg Edwards"
| wrote:
|
| Some buried wires
|
| Some?
|
| under a horizontal dipole, at a height of 1/4 or 1/2
| wavelengths,
|
| Why that high? Another Wives' tale? What about 1/8 or 5/8 (or even
| some fraction in between)?
|
| will, in theory
|
| Whose theory?
|
| , reduce losses.
|
| Clearly loose conjecture. You got any data, or is this merely
| rustling baking crumbs out of your apron?
|
| 73's
| Richard Clark, KB7QHC
|
|