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Vertical Monopoles Using Buried Radials




 
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Author Topic: Vertical Monopoles Using Buried Radials  (Read 1934 times)
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R. Fry SWL
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« on: June 28, 2019, 05:51:46 AM »

As an "FYI," below is a set of extracts collected from the textbook Radio Antenna Engineering by Edmund Laport, Chief Engineer, RCA International Division and Fellow of the Institute of Radio Engineers (McGraw-Hill, 1952).

Some of its details may be different than popular concepts about the way these antenna system configurations function.

The last sentence of the last paragraph below is particularly important information about these systems.

-----

2.5. Ground Systems for Broadcast Antennas

Antenna performance is standardized with reference to the ground being a perfectly conducting, flat plane. Such an assumption serves a very useful purpose in revealing the ultimate possibilities of a certain radiator in terms of its dimensions and longitudinal and sectional geometry at a given frequency. All practical deviations from this norm are due to a number of empirical circumstances, of which one is the earth itself.

A line of electric force (displacement current) extends from the top of the antenna through surrounding space to the earth. Upon entering a perfectly conducting earth it becomes a conduction current which returns to the base of the antenna and becomes a portion of the antenna current. The electric lines of force of the antenna field are thus seen to be the continuation current of a closed circuit through surrounding space. A vertical radiator above natural earth without any sort of ground system, energized by an electromotive force between the antenna and the earth, would require all earth currents to return to the antenna through a very imperfect conductor.

The earth currents return to the base of a vertical antenna along radial lines. At the base of the antenna, all the ground currents add together to enter the antenna as the antenna current. The total ground loss is the integrated losses at all points due to all the returning ground currents. In ordinary soils this loss is considerable, and measures have to be taken to minimize ground loss by the use of systems of buried radial wires that conduct the returning ground currents to the base of the antenna through high-conductivity circuits.

The distance from the antenna at which returning ground currents are of such a low value as to be negligible is on the order of 0.5 wavelength. Beyond about 0.4 wavelength, the gain in efficiency with increased length is seldom a good economic investment, when a sufficiently large number of radials is used.

Systematic measurements have shown that the effective length of a buried wire decreases as the number of radial wires is decreased.  Ground resistance decreases as both the length and the number of buried radial wires are increased.  However, when the number of radials exceeds 120 and their length exceeds 0.4 wavelength, one reaches the region of diminishing returns. With such a ground system, the circuital and radiational characteristics of a vertical radiator of the type used for broadcasting approach very nearly those computed from theory for a perfectly conducting earth.
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KK4YY
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« Reply #1 on: June 28, 2019, 07:38:52 AM »

Is Laport saying that the point of diminishing returns is analogous to very nearly approaching theoretical perfection?

I also note that he uses the term 'earth' not 'Earth'. The former, presumably, to refer to the soil in which the radial wires are immediately buried, as opposed to the entire planet Earth. However, using the term 'earth' may lead to a misinterpreted reading; a reader concluding that the radial system, as detailed, would provide for a nearly perfect global sphere of conduction (the Earth).

To my reading, Laport wanted to have the last word on the subject. And in writing that last sentence, one might argue that he succeed.


Don
(Not and engineer, not affiliated with RCA, and not getting paid to write an authoritative book)
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R. Fry SWL
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« Reply #2 on: June 28, 2019, 08:12:32 AM »

... To my reading, Laport wanted to have the last word on the subject. And in writing that last sentence, one might argue that he succeed.

Thanks for your comments.

Laport's final sentence there is consistent with the results of the earlier experiments and detailed paper titled GROUND SYSTEMS AS A FACTOR IN ANTENNA EFFICIENCY written by Brown, Lewis & Epstein of RCA Labs, and published in the June 1937 issue of the Proceedings of The Institute of Radio Engineers.

It is also supported by the field intensity measurements of broadcast consultants and radio station engineers over many decades, using calibrated field intensity meters and NEC4.x MoM calculations (see the graphic below).



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KK4YY
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« Reply #3 on: June 28, 2019, 09:50:33 AM »

Personally, I'm a proponent of elevated radial systems. They too, have been used effectively in broadcast applications when circumstances dictate, but for amateur use, elevated radial systems are far more cost effective. In my opinion, having 120 buried radials on an amateur vertical antenna installation is more for self satisfaction and bragging rights than engineering necessity. All that buried wire could be put to better use.


Don
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R. Fry SWL
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« Reply #4 on: June 28, 2019, 10:13:22 AM »

I agree -- 4 or more elevated, 1/4 WL radials can give the same system performance as 120 x 1/4 WL buried radials.
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WU2D
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« Reply #5 on: June 29, 2019, 09:07:32 AM »

There is Amateur Best Practice, Expert Best Practice, and Commercial Best Practice. Each have their proponents, norms. and associated risk to the investor.
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Steve - K4HX
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« Reply #6 on: June 29, 2019, 05:01:14 PM »

If, and only if everything is perfectly balanced and symmetric, both physically and electrically.


I agree -- 4 or more elevated, 1/4 WL radials can give the same system performance as 120 x 1/4 WL buried radials.
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KK4YY
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« Reply #7 on: June 29, 2019, 06:17:54 PM »

Here's Dr. Beverage on the subject...

* NEW AM BROADCAST ANTENNA DESIGNS.pdf (322.53 KB - downloaded 91 times.)
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« Reply #8 on: July 08, 2019, 09:25:26 PM »

Not to be confused with Harold Beverage, inventor of the Beverage antenna.
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KK4YY
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« Reply #9 on: July 09, 2019, 08:50:17 AM »

Mea culpa. I made that very mistake. Clarence was Harold's nephew.
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« Reply #10 on: July 09, 2019, 10:50:23 AM »

And more radials, more Q.

I've found that 8 is optimum for being able to QSY easily within the band.

73DG
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KK4YY
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« Reply #11 on: July 09, 2019, 11:22:00 AM »

I remember reading an article, some years ago, where various numbers of elevated radials were tried and the results plotted. I don't recall the source of that article, but the upshot was that somewhere in the 6 to 8 radial area provided a good compromise, all things considered.

I can't find that article now, so I'm relying on my recollection for what it's worth.


Don
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W4EWH
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« Reply #12 on: July 09, 2019, 12:06:56 PM »

In my opinion, having 120 buried radials on an amateur vertical antenna installation is more for self satisfaction and bragging rights than engineering necessity.

I agree, with one exception: those with CC&R's on the deeds who must load their flagpole would need buried radials, and it helps to know that 120 radials at .4 wavelengths each is the goal to aim for.

By the way, I've always been curious about the "120" figure: I would have thought that radials could be more easily installed by repeatedly bisecting the distance between the previously installed radials, so as to arrive at 128 radials instead of 120. I guess I've been around computers too long.

Bill, W4EWH

P.S. Does anyone know the windows "alt" code for lambda? I tried 0955, without success.
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« Reply #13 on: July 09, 2019, 12:16:53 PM »

Keep in mind the AM BC world is built around fixed formulae to generate a specific mV/m at a certain distance @ a certain power input on a single frequency (not counting diplexed/triplex arrays).

Amateurs are more concerned with costs, abilities, restrictions, and usability--not so much on fitting any such 'form'.

If one goes to all the trouble & expense to put up a vertical, the most important thing is 'Does it work to my advantage?'  Can I use it at different spots on the band?  Does it get out better than a simple dipole?

In short, lots of radials--toss yer VFO and stick to one freq. Otherwise you'll be out at the doghouse, retuning the thing every time or rigging up some type of motor-driven gizmo trying to make that silk purse out of the sows ear.

73DG
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KK4YY
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« Reply #14 on: July 09, 2019, 01:09:56 PM »

P.S. Does anyone know the windows "alt" code for lambda? I tried 0955, without success.

Lambda:
UPPERCASE = Λ
lowercase = λ

I never could figure out how to type it, but I know how to copy/paste it.
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« Reply #15 on: July 09, 2019, 03:00:14 PM »

https://www.keynotesupport.com/websites/greek-letters-symbols.shtml

Pretty much covers them all.


--Shane
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« Reply #16 on: July 09, 2019, 03:03:10 PM »

I remember reading an article, some years ago, where various numbers of elevated radials   ...

I can't find that article now, so I'm relying on my recollection for what it's worth.
Don

Rudy Severns,  N6LF  has written extensively about Elevated Radials,   as published in QEX:

https://www.antennasbyn6lf.com/2012/02/elevated-radial-ground-systems-some-cautions.html

FWIW,   Vic
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KK4YY
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« Reply #17 on: July 09, 2019, 05:52:03 PM »

I remember reading an article, some years ago, where various numbers of elevated radials   ...

I can't find that article now, so I'm relying on my recollection for what it's worth.
Don

Rudy Severns,  N6LF  has written extensively about Elevated Radials,   as published in QEX:

https://www.antennasbyn6lf.com/2012/02/elevated-radial-ground-systems-some-cautions.html

FWIW,   Vic



That's the one! Thanks, Vic. Smiley
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