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Author Topic: Counterpoise and radials  (Read 1964 times)
AA4PB
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« Reply #15 on: June 16, 2005, 10:06:54 AM »

Can someone point me to a reference that indicates that one wire is a counterpoise and multiple wires are radials without regard to where they are placed?

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2E0ESW
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Posts: 27




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« Reply #16 on: June 16, 2005, 10:19:16 AM »

AA4PB,
Sorry mate I'm as confused as you are (hi  hi)

73
Etienne Swanepoel 2E0ESW
Bude
Cornwall
UK
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2E0ESW
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Posts: 27




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« Reply #17 on: June 16, 2005, 10:25:39 AM »

K5DVW,Thanks for your answers
Etienne Swanepoel 2E0ESW
Bude
Cornwall
UK
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K5DVW
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Posts: 2193




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« Reply #18 on: June 16, 2005, 11:17:19 AM »

AA4PB> I think the classic definition of the word counterpoise refers to a usually single wire run from the back of a tuner. That's what I've always considered a counterpoise.

A radial is what you find at the base of a vertical antenna and you most always find more than one of them laid out in a radial fashion from the feedpoint. I can't think of a vertical antenna (that worked worth a hoot) that had a single wire radial.

I do think some manufacturers of antennas confuse the two terms. They also make crazy gain claims.

An RF ground, well that can be a counterpoise OR a radial field.
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AA4PB
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« Reply #19 on: June 16, 2005, 12:06:22 PM »

I think the classic definition of the word counterpoise refers to a usually single wire run from the back of a tuner. That's what I've always considered a counterpoise.
------------------------------------------------------
I agree that a single, insulated wire connected to the ground side of the back of a tuner is a counterpoise. I think its a counterpoise because it is not in direct contact with the ground rather than because it is a single wire. If you look at the definitions in some of the older ARRL books (and related references on several Internet sites) you find that they define radials as being in direct contact with the ground (either laying directly on or burried just below the surface) and a counterpoise as a system of conductors that located on insulators above the ground and is only capacitivly coupled to the ground.

Of course you will also find much information (especially from antenna manufacturers) that use radial and counterpoise interchangeably. Some even call their system radials/counterpoise.

The bottom line is that radials and a counterpoise accomplish the same thing and so I think the questions have two correct answers.
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K5DVW
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« Reply #20 on: June 16, 2005, 12:29:25 PM »

AA4PB > I agree that the questions are somewhat nebulous. It can be real confusing when you try and think of all the ways counterpoise and radial are used.

So, I wonder what the 'right' answers were and why?
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W9OY
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« Reply #21 on: June 16, 2005, 08:24:00 PM »

I don't think these question are vague in the least.  I think they directly address the nature of a vertical antenna.  I don't think the questions have anything to do with single wires or connections to the ground lug of antenna tuners.

A vertical has a radiator and it has what ever mass the radiator is imaged back into to complete the circuit.  The radiator is usually made from metal and is efficient.  The counterpoise can be metal or salt water or dirt or rocks, or the shield of the coax or 120 pieces of 1/2 lambda of wire, a combination of these things, or what ever entity that the current flows in when the RF is applied.  If the entity is a wet noodle or a granite bolder, the counterpoise  isnt very efficient.  If it is square mile of solid silver plate it is very efficient.  If at 3.5MHZ you plot a 10ft vertical radiator and a 60ft vertical radiator over the same counterpoise you get the same pattern.  The field strengths are different but the shape of the pattern is virtually the same.  

A radial is a conductor that lays along a ray that bisects a circle through the center point.  How the radials are laid out effects the antenna's pattern.  If you lay out 1 radial the pattern is oval in shape.  If you lay out 2 radials at right angles it is an oval that shifts its axis 45 degrees.  If you lay out 120 evenly spaced radials the pattern is circular.

Why make it hard?  The questions I think are clear.  

73  W9OY
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K5DVW
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« Reply #22 on: June 17, 2005, 05:46:15 AM »

W9OY> Remember the pattern of a vertical dipole in free space. The pattern is a donut looking thing, right?

Ok, now bend the bottom conductor out 90 degrees. No more donut shape. The pattern is distorted with one wire or counterpoise (my definition). Move the single wire around, or crinkle it up, the pattern changes, but the feedpoint resistance doesnt change. Pattern is affected! Is this one wire a counterpoise or a radial?

Now, add a symmetrical wire to the thing directly opposite the first 90 degree one so you have two opposite ones, the nominal donut shape is back. Add 200 more of them, the donut shape remains. Hence, if you're willing to accept that radials occur in number more than 1, they don't affect the nominal radiation pattern.

Then, check out the radiation resistance of a ground mounted vertical with 2 vs 20 radials. There's a huge difference in field strength, but not a huge difference in pattern. So, radials affect efficiency, not pattern.

I do agree somewhat that counterpoise could mean any number of things. But, when you put counterpoise AND radials in the answer, it's hard to know which one is technically correct.

The problem with the questions are in how they define a counterpoise. They should have said "single wire counterpoise" or "x number of radials" or some such qualifier.
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N1OD
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« Reply #23 on: June 17, 2005, 06:16:27 AM »

W9OY>  That was how I interpreted the question, hence my answers.  "Counterpoise" does not refer to a single conductor, but the groundplane.

Paul N1OD
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KA5N
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« Reply #24 on: June 17, 2005, 07:40:48 AM »

To score well on the exam, you have to give the answer that the makers of the exam consider "correct."  It makes no difference what we USA hams think is correct.  So again I suggest you inquire of the RSGB or whatever authority in GB that makes the exams for a definition of counterpoise and radial because as it has been pointed out you could answer each question either way depending on those definitions.
Allen
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W9OY
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« Reply #25 on: June 17, 2005, 08:50:32 AM »

here are the common definitions of counterpoise and their references:

These come from doing a google search on this search term  "define: counterpoise"  copy this exactly into google without the quotes if you want to do it yourself.

<Definitions of counterpoise on the Web:

counterweight: an equivalent counterbalancing weight
www.cogsci.princeton.edu/cgi-bin/webwn2.1

The second half of an antenna, which "balances" the radiating element to launch the RF wave. Although not always readily apparent, a counterpoise always exists and its suitability can greatly affect the efficiency of the antenna. A ground plane, as found on ground plane antennas, is one type of counterpoise, as is the outer case or circuit board of a receiver using an attached whip antenna.
www.audiotechnica.com/glossary/

A state of equality between opposing forces.
www.yourwebassistant.net/glossary/c17.htm

The reference-plane portion (grounded or ungrounded) of an unbalanced antenna.
www.visionneeds.com/glossary.htm

Offset; balance; counterbalance; act as an equal effect.
https://www.mises.org/easier/C.asp>

Note none of these definitions refer to a single wire.  They refer to a concept.  And none of the definitions refer to pattern.  They do refer to efficiency.  The single wire definition is simply your definition of a counterpoise.  A single wire is a subset of the superset of counterpoise, but it is not the entire set of counterpoise.  It is a specific example of one kind of counterpoise.  As such I don't think it gets at what the question is asking.  Certainly a single wire opposite the radiator in free space is a very efficient counterpoise, so is an infinite plate in free space.  Note the reference to efficiency in both of these examples.  You can extend the analysis to dirt, sand, rock, salt water, fresh water etc.  Each of these analyze around efficiency.  A silver plate in free space> salt water > radial field > good earth > sand etc.  This is a very common analysis that all hams know about, and the kind of thing a body that examines hams would consider asking.  So I think efficiency is the common feature being addressed in this question.      

A radial system is a specific kind of counterpoise that is intended to approximate a solid plate.  The shape of the radial system affects the pattern.  Given these definitions I think the questions become clear.  If there are great variations in the conductivity of the plate across its surface the radialted pattern takes on a shape decidedly different than circle.  Since the question is specifically refering to pattern, I think the choice of the word that specifically refers to an antenna element that can affect pattern is the correct choice.  

If the question added this choice "reflector" what would you choose as the answer?  Remember the question expects you to pick the "best" choice.  If you add the word reflector that becomes the best choice.  Radial becomes the next best choice and counterpoise becomes the third best choice.

Power can effect efficiency.  It occurs if the components in an antenna are under rated, where power instead of being radiated goes into melting or arcing components.  Modulation can affect efficiency in the case of very narrow bandwidth antennas, but neither of these things are mentioned in the questions.  Neither power or modulation affect pattern.

So this is my analysis of the questions, and I think you can clearly defend these answers before any testing body.

73  W9OY  
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K5DVW
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« Reply #26 on: June 17, 2005, 11:11:20 AM »

W9OY> Ok, I appreciate your definitions. Let's run with them for a second.

A counterpoise can be radials, it can be a single wire, it can be a plane, a water pipe, it can be a whole host of things.

For grins, I checked on the IEEE website. They have several antenna articles mentioning counterpoise. In one case, a single wire. In another case, a random set of wires in a crows foot pattern generally going in the same direction. Apparently they dont like the word "counterpoise". Wonder why?

They do the right thing and call ground planes what they are and define them properly. The word counterpoise is too nebulous for science, or exam questions.

Frankly, I think both questions shouldnt have counterpoise and radials in the answers and one could argue either one is correct.

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2E0ESW
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Posts: 27




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« Reply #27 on: June 17, 2005, 12:06:26 PM »

My thanks to ALL who so actively and investigatively addressed the issue. The data, comments and references provided are most helpful.

Thank you
Etienne Swanepoel 2E0ESW
Bude
Cornwall
UK

PS  If I get such a question I shall post it and the answer.
73
E.S
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AA4PB
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Posts: 12644




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« Reply #28 on: June 17, 2005, 12:41:09 PM »

From the SGC web site: "Vertical antennas can have radials mounted on or below the surface of the actual ground. If the radial system is mounted above the ground, it is technically a counterpoise and takes the place of the actual ground."
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