An Insight

[kl7aj]

Everybody should read L.B. Cebik (W4RNL)'s stuff. Recently, L.B. wrote a great dissertation to show that there is no such thing as a "counterpoise". What we call a counterpoise is just random garbage that is coupled to an antenna that we haven't thought much about. When it is all said and done, (and NEC antenna modeling bears this out) the radiation pattern of ANY antenna, balanced or not, is simply the vector summation of currents and their phases. A counterpoise is just additional wire in an antenna. What we consider "ground" is totally arbitrary.

Here's a good "thought experiment". Let's take a car that's 8 feet long. We'll mount an 8 foot vertical whip on the rear bumper, with appropriate loading coil. We'll put the whole shebang out in space, so we don't have to worry about coupling to the Earth.

Now, conventional wisdom tells us that the car body is some kind of "counterpoise" while the whip is what radiates. Not true! The 8 foot car body radiates EVERY bit as effectively as the 8 foot whip! In fact, our radiation pattern will be the same as that of an inverted Vee, lying on one leg. It will have maximum radiation along the bisector of the vee....45 degrees above the "horizon." (and 45 degrees below the horizon in the "backwards" direction.)

So...things are not what they seem. We need to get back to some clearheaded logical analysis. I am most grateful for hams like W4RNL and W8JI, who faithfully "hold our feet to the fire," as it were.

I am reminded of the words of my favorite author, Ernest Hemingway. He said, The most essential gift for a good writer is a built-in, shockproof sh** detector."

Truer words were never spoken.

eric

[K1VSK]

Any link to the article to which you refer?

I for one would be very interested in reading it as I believe my experience, albeit limited, clearly demonstrates the efficacy of a counterpoise. The measured field strength observations on which my opinion is based provides me with some empirical evidence which I can't ignore simply because someone says so.

[kl7aj]

http://www.cebik.com/gp/cps.html

[K1VSK]

tnx for the link - it is interesting but it is more a history (and clarification) of the terminology rather than a counterpoint argument.

[KI4NGN]

I've been lambasted by some hams when I've said that there is no such thing as a monopole antenna, that whatever one may consider to be the radiator, all antennas are based upon a dipole and there must be the other side of the dipole, whether it's the ground, a wire in the ground, a wire laying on the ground, your household ground, the body of your car...whatever. Current must flow if an antenna is going to radiate, and there is no such thing as current flow with only one pole.

It doesn't matter what you call the other half of the dipole, and I agree that "counterpoise" is just used to describe the half of the dipole for which no design consideration has been given as has been done with the "radiator".

Mike

[WA9SVD]

Try the entire Cebik web site. There's no "one" article there that's important, intreesting, or informative; they all are.

[PA5COR]

Been reading up there for ages.
As in the ARRL/RSGB antenna books, Rothammel etc.

He's an very good source.

[W1GUH]

I've always thought of the radials of a quarter-wave vertical as the "other side of a half-wave dipole." I've put that to practical use many times when I've had a temporary vertical where there was only room for one radial, and those always worked "pretty well." And what's the impedance of the end of a quater-wave piece of wire? 0 ohms....just like ground. How about that?

Counterpoise, radial, "other half of a dipole", ground (artifical or real), pretty much the same when it comes to working against an antenna. Using a random wire? Got no good ground? Try a quarter-wave piece of wire for a ground...or even tune a random piece of wire to look like a quarter-wave (as in artificial ground). You'll do fine.

[W2BBQ]

Hmmm, then what is going on with a 1/2 wave vertical. Either as a home antenna or say a marine antenna on a fiberglass boat. Where's the "other half?"

TNX


W2BBQ

[G0GQK]

I read that article a few weeks ago. What i don't understand is that he stated that radials don't radiate. If that is the case why for instanceare radials put on a Cushcraft R5 and why are we told to raise them so as not tocause problems for people and animals? RF goes into them so why wouldn't raised radials radiate ?

G0GQK

[kl7aj]

Hmmm, then what is going on with a 1/2 wave vertical. Either as a home antenna or say a marine antenna on a fiberglass boat. Where's the "other half?"

TNX


W2BBQ

A half wave vertical is just a vertical dipole.....it's just that it's voltage fed...but fundamentally the same. The ground actually doesn't do anything for you.

[kl7aj]

I read that article a few weeks ago. What i don't understand is that he stated that radials don't radiate. If that is the case why for instanceare radials put on a Cushcraft R5 and why are we told to raise them so as not tocause problems for people and animals? RF goes into them so why wouldn't raised radials radiate ?

G0GQK


There actually IS radiation close in, but since the currents are flowing in opposite directions, in the far field they cancel out. If you are within a half wave or so of a radial (and off to one side) there is radiation. At the very CENTER (right underneath the vertical part) there will be none.

This is easy to demonstrate with a current probe. I have an upcoming article in QST (collaboration with John Stanley) on Antenna current probes. Stay tuned.

eric

[w5alt]

Yep, that's one of the things I've learned over the years, too. Everything attached or coupled to your antenna and ground is part of the antenna system. Failure to recognize that can lead to some very strange misconceptions and hard to diagnose problems. In addition, since in most rigs, the shield side of the coax antenna connector is connected to the rig ground and chassis, everything attached to your rig may well be a part of your antenna, too, whether you want to call it that or not.

A few hours spent with an RF current sensor can be a very enlightening experience!

73,
Walt, W5ALT

[KI4NGN]

Hmmm, then what is going on with a 1/2 wave vertical. Either as a home antenna or say a marine antenna on a fiberglass boat. Where's the "other half?"

TNX


W2BBQ

Everything connected to the ground side of your rig's antenna connection is the other half of your vertical dipole.

[kl7aj]

Everything connected to the ground side of your rig's antenna connection is the other half of your vertical dipole.

We should probably qualify that statement with the following clause....."unless deliberate measures are taken to prevent coupling..."

A good example is a J-pole. A properly tuned J-Pole will have unmeasureable common mode currents on the feedline. The bottom 1/4 wave is a tuned stub that has INFINITE impedence at the top end.

A variation on this theme: A perfectly good balun and a perfectly balanced horizontal dipole is not an absolute guarantee of no transmission line currents! You can RE-COUPLE r.f. onto the feedline if it runs parallel to the dipole...even if there is NO common mode current passing by the balun. A dipole has to be physically AND electrically balanced to prevent feedline radiation.

eric

[ab0wr]

As far as radials not radiating, the radials don't actually make up the "other half" of the antenna, at least if I remember my 40year old electromagnetics class right.

The ground provides a sort of a "mirror" where the other half of the dipole "virtually" appears. The better the ground the less the loss associated with that virtual side of the dipole. Since the ground, even with a lot of radials, still has a lot of loss, it just appears that the "ground" (i.e. the radials) doesn't radiate.

I haven't read Cebik's paper yet. It will be interesting to see if he agrees.

tim ab0wr

[W2BBQ]

Ah....mmmmmm.....not sure I'm buying the answer regarding 1/2 wave verticals.

Anywho, how about a full-wave loop skywire. Where's the dipole in that? Other half of the antenna?

[kl7aj]

As far as radials not radiating, the radials don't actually make up the "other half" of the antenna, at least if I remember my 40year old electromagnetics class right.

The ground provides a sort of a "mirror" where the other half of the dipole "virtually" appears. The better the ground the less the loss associated with that virtual side of the dipole. Since the ground, even with a lot of radials, still has a lot of loss, it just appears that the "ground" (i.e. the radials) doesn't radiate.

I haven't read Cebik's paper yet. It will be interesting to see if he agrees.

tim ab0wr

The MIRROR effect is actually a very large scale effect and cannot be simulated by a close in radials (or any man made ground, at least at H.F. wavelengths). There's a LOT that takes place in an antenna system FAR beyond the limits over what you have any control. To have an R.F. mirror, you need essentially an infinite conductive plane (though not necessarily a very GOOD one)...but it has to be many wavelengths in each direction. (In interior Alaska, the effective "mirror" is between 30 and 60 feet below grounds level...which is why you can pretty much lay a dipole right on the ground and it works fine!)

[kl7aj]

Ah....mmmmmm.....not sure I'm buying the answer regarding 1/2 wave verticals.

Anywho, how about a full-wave loop skywire. Where's the dipole in that? Other half of the antenna?


A full wave loop is a complete antenna, it doesn't need to "find" another terminal.

Incidentally, a very short, center-loaded antenna, (such as two mobile whips end to end, or a W0SVM "shorty-forty" is also a complete antenna.

The real point is that there is nothing special or magical about a counterpoise. It's just more wire in your antenna....it can work for you or against you.

[W2BBQ]

A ha! Thanks for helping us a find an antenna that isn't in some way or shape based on a dipole, which was earlier stated that included EVERY antenna.

[KI4NGN]

No such thing was found. A full wave loop is a close dipole: it doesn't need to "find" another terminal because it is connected directly to the other terminal. There are still two poles. There can be no current flow with only one pole: current has to flow from and to somewhere.

[N2RJ]

Hmmm, then what is going on with a 1/2 wave vertical. Either as a home antenna or say a marine antenna on a fiberglass boat. Where's the "other half?"

TNX


W2BBQ

Your feedline's shield will act as a counterpoise.