Regarding antennas, what does counterpoise mean?

[The DB]

Here is a link to a guy looking for the experiment you note above. It was published in CQ, April, 1984.

TopBand: W3ESU/K8CFU 'minipoise' - any info?

Here is another article about the test these same guys did and it has some history too.

http://www.w1npp.org/events/2010/2010-F~1/ANTENNAS/HF-VER~1/830202~1.PDF

db, I also think I have the article you noted entitled: "Vertical Antennas: New Design and Construction Data."

It is 5 pages long, front and back.

The book (ARRL Antenna Book, 16'th edition) does list those three authors, and the less than a page about it available to me says full results are available in The ARRL Antenna Compendium, Volume 2. The pictures in the book are from the same source, and don't match what is in the article from the same people you linked. There is less than a page of information directly related to the subject in the antenna book.


The DB

 

[The DB]

I also took note of the suggestion in the article you referenced of there being yet another method of implementing the counterpoise than what we have discovered. While it wasn't perfectly clear to me, it did seem to say that one could improve the effects of the counterpoise over certain soils by having both a ground mounted radials system and a raised counterpoise immediately above that.

I thought this sounded familiar so I looked through an old thread on this forum called The whole truth, and nothing but the truth - Counterpoise. The following is a quote from me on post number 21 in that thread:

I'm guessing this would change with frequency. I am also guessing that that the quality of the ground would make a difference as well, as a more conductive ground would naturally allow for more capacitance and thus allow for similar results with a smaller radial system. A more conductive ground would also allow a radial system to be further away (higher if you will) and still have the needed capacitance between ground.

Question 4) What happens when it rains? That would change the conductivity of the ground beneath the radial system would it not? Would it also change the tuning of said antenna? If I were to build such an antenna would it be worth my time top stabilize and/or potentially increase the typical conductivity of the ground in question?

I thought sure I also made a reference to a second set of grounded wires, and either buried or laying on the ground being a potential benefit as they would raise the conductivity of the ground below. While my quote above does talk about the conductivity of the ground below the counterpoise, I can't seem to find where I referred to a second set of wires. It must have been something I though of and never posted...


The DB

 

[northern35s]

The book (ARRL Antenna Book, 16'th edition) does list those three authors, and the less than a page about it available to me says full results are available in The ARRL Antenna Compendium, Volume 2. The pictures in the book are from the same source, and don't match what is in the article from the same people you linked. There is less than a page of information directly related to the subject in the antenna book.


The DB

I have vol2 pdf if you you're interested

 

[CowboyCody]

I am a bit of a late comer, and my technical knowledge is limited, and I know that this is a discussion about the terms used. But it made me think about a picture I saw in an article I read about the WLW station. I have to wonder if the "Guy wires" that kept the tower erect didn't create an unintentional counter poise of sorts. Most commercial stations have them. Weather they have been named, or intentionally created or not I don't know. I would say that either way the antenna will "find" its own counter poise.

Here is a few pics of the tower
Visit to WLW -

One thing I have always been curious of is how crucial the length of the "other half" of the antenna actually is. I wonder if the fraction of a wavelength rule that many use has any real effect in the real world. I would think longer is better may apply here.

 

[The DB]

I am a bit of a late comer, and my technical knowledge is limited, and I know that this is a discussion about the terms used. But it made me think about a picture I saw in an article I read about the WLW station. I have to wonder if the "Guy wires" that kept the tower erect didn't create an unintentional counter poise of sorts. Most commercial stations have them. Weather they have been named, or intentionally created or not I don't know. I would say that either way the antenna will "find" its own counter poise.

Here is a few pics of the tower
Visit to WLW -

One thing I have always been curious of is how crucial the length of the "other half" of the antenna actually is. I wonder if the fraction of a wavelength rule that many use has any real effect in the real world. I would think longer is better may apply here.

Many towers use couplers to break up the electrical lengths of the guy wires with the intention that they not act as part of the antenna. I would imagine that that is not always possible. Even then, most of the guy wire is typically to high to be capacitively coupled with the earth below.

When dealing with resonant lengths of "the other half" the antenna is resonant when both the radiator and "the other half" combine to be resonant. We typically try and make both sides resonant, however, the article does talk about varying the size of "the other half" to compensate for the vertical element being a little to long or a little to short. It deals with 2 meter quarter wave antennas as I recall, and had a short 5/8 wavelength section at the bottom. When I get some time I'll see if I can find it and post a link for you.


The DB

 

[CowboyCody]

That's interesting, I did not know they purposely isolated the guy wires. I agree that it is good to have the antenna balanced, but what about when the coax shield or vehicle body becomes the other half? This situation is not a resonant length... Is it perfect? No but it does work fairly well. But then again this is not a true "counter poise" or "ground plane" in the mobile the body of the vehicle becomes more of a barrier between the antenna and the lossy ground if I understand it correctly.

 

[The DB]

I agree that it is good to have the antenna balanced, but what about when the coax shield or vehicle body becomes the other half? This situation is not a resonant length... Is it perfect? No but it does work fairly well. But then again this is not a true "counter poise" or "ground plane" in the mobile the body of the vehicle becomes more of a barrier between the antenna and the lossy ground if I understand it correctly.

Actually, the chassis/body of a car is one of the few things that some people call a counterpoise and are actually correct, but typically for the wrong reason.

The body of the car is attached electrically to the shield of the coax, and provides capacitance with the earth below. The biggest problem today is the chassis and frame are often both painted before they are put together, which isolates them from each other electrically, and thus they act as different units. RF Bonding is a solution to this, and is done surprisingly rarely in todays world where people are looking for that every little bit to help their signals.


The DB

 

[CowboyCody]

That's funny, I had it flip flopped in my head.... Even after reading all this:blush: I think I have it now. As for bonding, I did it in my F250 Powerstroke and it made a world of difference as far as engine noise, I'm not sure about transmit but it had to have helped there also.

 

[northern35s]

There's a lot more going on with a mobile installation than we may first imagine, this image depicts some of what is going on, along with the equivalent circuit:

This image appears in Les Moxon's, G6XN, book HF Antennas For All Locations, and whilst it is a book that contains many a 'ham' antenna, some of his explanations about terrain and propagation makes for essential reading, he's probably most famous for his work on the Moxon Rectangle.

 

[HomerBB]

Thanks for the post, northern.
If you could bring the legend over into the post for those of us who don't know how to translate them into words it may be helpful. Or simply add explanations so it has a bit of flavor for those wondering what Moxon is explaining with it.

 

[northern35s]

Thanks for the post, northern.
If you could bring the legend over into the post for those of us who don't know how to translate them into words it may be helpful. Or simply add explanations so it has a bit of flavor for those wondering what Moxon is explaining with it.

He is discussing the earth losses of a mobile installation and goes on to explain ways of minimising this, the latter would sidetrack the thread somewhat, however, I'll do my best to explain.

This is an inductively shortened HF antenna, by that I mean it has a coil somewhere along it's length, there is capacitive loss between the antenna and the car body Ca, there is a capacitive loss between the car body and the ground below Cb, there is a resistive loss in the earth below the car body Re (normal earth / dirt being a poor conductor) and a series capacitive loss of the antenna to earth CaI.

The diagram below the car shows these losses and components in a circuit diagram, the two addition items we see in the circuit is Rr Radiation Resistance of the antenna and La which represents the loading coil of the antenna.

HTH

 

[HomerBB]

Thanks.
So for those wondering, you placed it in the thread to demonstrate the the actively capacitive relationship between the antenna, car body, and the ground/earth. This helps us to see that the antenna system is not simply the antenna, and car body. It demonstrates from another perspective the why of the car body being a counterpoise. What is not in the illustration is the flip side of the capacitive losses that are inevitable with an antenna mounted so near to earth - the advantage of the capacitive bond to the earth that will limit the losses to a manageable extent.

What is interesting to me for the sake of the thread is that Moxon sees the RR - radiation resistance - without which no antenna will disperse a signal into the air, in the earth component of the tri-unity of this mobile antenna system. Without the capacitive linking of the of the upper antenna components, the car body and the antenna, with the earth there is no functional antenna system.

Of course, as an aside, it shows why putting mobile antennas on bumpers or other extremities off-center to the mass of the automobile body is at best a bad idea, and at worst a recipe for a complete disaster in terms of losses to earth and performance degradation.

 

[northern35s]

On the mobile theme, and sorry for the thread creep, a coil at the base of an antenna requires less inductance than one in the centre of the antenna, why? because there is greater capacitive loss in the coil at the base of the antenna than there is in the centre, it reduces coil Q, and for similar diameter coils made of the same diameter wire, a base loaded antenna will have a greater bandwidth.

And here's one I haven't experimented with yet, if you add antenna length below the coil, say take a wilson base loaded vertical and add a 1' shaft below the antenna, there should be little change in the VSWR, however your efficiency will increase, but your bandwidth will decrease.

Should really be a thread on it's own this one, sorry :blush:

 

[CowboyCody]

And here's one I haven't experimented with yet, if you add antenna length below the coil, say take a wilson base loaded vertical and add a 1' shaft below the antenna, there should be little change in the VSWR, however your efficiency will increase, but your bandwidth will decrease.

Should really be a thread on it's own this one, sorry :blush:

Wouldn't this basically be a "trucker" style antenna then? Like the Wilson 2000/5000?

 

[CowboyCody]

What is not in the illustration is the flip side of the capacitive losses that are inevitable with an antenna mounted so near to earth - the advantage of the capacitive bond to the earth that will limit the losses to a manageable extent..

Which brings up the million dollar question, how far above earth does a vertical antenna have to be to be efficient? I would assume a monopole antenna should be higher than a groundplane. I know I have always been told at least 1/2 wavelength and that a full wavelength is better. Of course this all depends on soil conditions.