Regarding antennas, what does counterpoise mean?

[northern35s]

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

Cody

My main interest is amateur radio, although I still use a CB radio at home for chatting with a couple of local friends, so my experience with some of the CB antennas is limited, especially the Wilson range, but I think I know the antenna you are talking about.

When we add an inductor to an antenna, in order to shorten it, we introduce loss, in an attempt to minimise those losses there are a number of things we can control, coil diameter, coil winding cross section, spacing between coil windings, length of coil, and most importantly, placement of the coil in the antenna, an efficient centre loading coil will always be better than an efficient base loading coil, that's just physics.

My own homebrew mobile antennas are 8' tall with a large centre loading coil just over 5" in diameter, that's a big antenna and one most people aren't prepared to mount on their car, however I don't care about the looks, efficiency and practicality are my prime motives.

Once again apologies for the thread creep and if admin would rather this be a subject of it's own then I'm cool with that


A picture is worth a thousand words, my homebrew multiband special, and no, it isn't any good for moonshine.

 

[northern35s]

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.

That all depends on what you understand by the term efficient, a ground mounted vertical antenna can be almost 100% efficient, the effect of Earth doesn't disappear at height and it isn't necessarily the ground / dirt below the antenna that enhances efficiency, it may well be the dirt hundreds of wavelengths away from the antenna in the far field or Fresnel zone

 

[The DB]

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.

That matches an image found in some editions of the ARRL Antenna Book, except this is a more general image, not specifically a car.

The DB

 

[The DB]

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

Up to a point, as you raise the load (coil) higher on the shortened antenna the efficiency goes up. So going from a base loaded Wilson 1000/5000 to a Wilson Trucker 2000/5000 that has a shaft will increase the antennas efficiency. For the same shortening effect, as you raise the load (coil) higher on the antenna it needs to be larger to accomplish the same ammount of shortening. Also as you continue to raise the load (coil) up higher and higher your gains in efficency per distance raised will drop off.

Another thing that would potentially change the efficiency of the base loaded versions is the mount type. Going from a magnet mount to a permanent bolted mount to hold up the Wilson Trucker style antenna would also be more efficient.

All that being said, I highly doubt you would notice the difference, unless you have a problem somewhere with one of the mounts. It takes much more of a difference for anyone to actually notice a change than most people realize.


The DB

 

[Marconi]

Up to a point, as you raise the load (coil) higher on the shortened antenna the efficiency goes up. So going from a base loaded Wilson 1000/5000 to a Wilson Trucker 2000/5000 that has a shaft will increase the antennas efficiency. For the same shortening effect, as you raise the load (coil) higher on the antenna it needs to be larger to accomplish the same ammount of shortening. Also as you continue to raise the load (coil) up higher and higher your gains in efficency per distance raised will drop off.

Another thing that would potentially change the efficiency of the base loaded versions is the mount type. Going from a magnet mount to a permanent bolted mount to hold up the Wilson Trucker style antenna would also be more efficient.

All that being said, I highly doubt you would notice the difference, unless you have a problem somewhere with one of the mounts. It takes much more of a difference for anyone to actually notice a change than most people realize.


The DB

DB, Amen to your last comment.

Among others, I think CB claims are often profound, claimed aplenty, and are often lacking in useful details.

As humans we tend to get excited about what we sometimes observe, and show some bias in what we think.

 

[HomerBB]

Cody,
Hopefully you can see that no one is avoiding a direct answer.
There are those generalities to which you referred that are the rules of thumb.

I think it needs to be kept in mind that the trend of this thread is with the counterpoise, what it is, and to some extent what it does that distinguishes it from other kinds of radials systems. So some of what is being written may lead to some associated thoughts, but may not of been speaking directly to what thoughts they generated in your head.

As for the counterpoise, it must be close enough to the ground to act as a capacitor plate with the earth. As for when some other device ought to be used in terms of how high, when the capacitive ground is no longer possible due to the distance between the earth and the radials network.


So, there is some rules of thumb for the counterpoise too, and we hope we might identify them with this discussion.

They are:

1. what is the counterpoise
2. how to construct the counterpoise
3. how to mount the counterpoise
4. what the purpose of the counterpoise is
5. when the counterpoise can be effective, and when some other device might be preferred

As it has been said for a mobile, as centered upon the mass of the entire automobile mass as possible so that the car body can be used as a capacitor plate most effectively.

It has been pointed out by many in numerous threads over many forums that an effective antenna is not necessary an efficient antenna.

My mama's rule of thumb is what guides me to learn more and then experiment when I can - "If anything will do, nothing will do as well"

northern, I realize the earth always has an effect upon RF. I also know that there is a point at which the counterpoise ceases to be a counterpoise because the distance above the earth is in excess of that from which a capacitive ground can be established. That is the point of discussion pertaining to the counterpoise we've been trying to clear up. Only a knothead would declare the earth to not be influential upon RF at any height. It is the earth that makes a discussion regarding height worthwhile.

 

[CowboyCody]

You guys have a much deeper understanding of theory than I will probably ever have. I find this all very interesting though. I'm sorry if I derailed it some. Back to topic!

 

[northern35s]

[/I]northern, I realize the earth always has an effect upon RF. I also know that there is a point at which the counterpoise ceases to be a counterpoise because the distance above the earth is in excess of that from which a capacitive ground can be established. That is the point of discussion pertaining to the counterpoise we've been trying to clear up. Only a knothead would declare the earth to not be influential upon RF at any height. It is the earth that makes a discussion regarding height worthwhile.

My comments were in response to Cody's understanding that a vertical antenna has to be at least 1/2WL high to be efficient, that isn't the case, there are situations where a ground mounted vertical can have a near 100% performance and very low take off angle, but this has everything to do the antennas construction and with the terrain, and not necessarily the dirt under the antenna

 

[HomerBB]

My comments were in response to Cody's understanding that a vertical antenna has to be at least 1/2WL high to be efficient, that isn't the case, there are situations where a ground mounted vertical can have a near 100% performance and very low take off angle, but this has everything to do the antennas construction and with the terrain, and not necessarily the dirt under the antenna

clear as a bell. thanks

 

[Marconi]

My comments were in response to Cody's understanding that a vertical antenna has to be at least 1/2WL high to be efficient, that isn't the case, there are situations where a ground mounted vertical can have a near 100% performance and very low take off angle, but this has everything to do the antennas construction and with the terrain, and not necessarily the dirt under the antenna

35, Homer says this is all clear to him, but your comment is not clear to me.

I can possibly make a judgment about the effectiveness or performance for how my antenna responds, by comparing to other locals in my area, but I can't put a % value on any of these terms, efficiency, effectiveness, or performance.

Disregarding the soil condition issues we've read about with Broadcast radio in this thread, are y'all considering this counterpoise idea can overcome the problems associated with ground clutter. 35, I think you mentioned the Fresnel zone idea. Is this and example noted below? It looks like he's talking a little bit about what I call clutter on the Earth's surface.

When I mount any part of my antenna below my average roof peak height I see noticeable attentuation...unless I can get very far away and well into the clear. I know increasing the height of an antenna that is placed well into the clear above this clutter will likely be a benefit too performance.

I also believe this counterpoise idea can show improvement in gain under some situations, over very poor soil for example and maybe on the tops of some of the building installations we seen in images. The idea also looks to show a little improvement in signal over buried or ground mounted radials...when they are mounted on or near the Earth too. But, I don't see the counterpoise idea being beneficial for 11 meters unless we make our comparisons in an open field with plenty of open space all around.

How do we measure near a 100% performance?

 

[northern35s]

Marconi, Cody was talking about efficiency, a full 1/4WL antenna can be near 100% efficient, that is, 100W into the antenna is 100W radiated from the antenna, no heating due to loading, a shortened vertical is less efficient, if we continue to reduce the antenna length, and increase the loading then it again becomes less efficient. It's a problem faced by many amateurs, but not necessarily most CBers, and it's especially affects anyone that works mobile, even then most CBers aren't prepared to use a 1/4WL antennas and rely on loading of some sort, vis a vis less than 100% efficient.

Currently ALL of my radio time is mobile, be that in my car or on foot, and as a result I see on a daily basis the affects of terrain, specifically terrain in the Fresnel zone, sometimes hundreds of wavelengths away from me. Here's a typical situation where terrain works in my favour; I was driving home from work one evening working DX on the 17m amateur band and there was an Alaskan station running quite a big pile up, remember I'm using a short antenna, a screwdriver antenna around 7' total length on the roof of my car, so it isn't 100% efficient, I don't know the percentage efficiency, but let's say 50%, my 100W in would be 50W ERP, I've lost 3dB already, so I'm using a negative gain antenna, let us say -3dBd gain. If we then consider the pile up this station was running, there were hundreds of people calling him across the globe, many probably using much more power than me, many using much bigger, high gain antennas than me, how could my -3dBd ever possibly compete with these signals? Simple, terrain, using the terrain to enhance my signal, increasing the low angle gain, just imagine if I could focus my 50W ERP onto the horizon, a really low angle, then I'd stand a chance.
Now I know the journey home from work, and I know whereabouts my signal gets this gain, and in which direction it favours, I needed a hill with the ground sloping down away from me to the North, there's only two places this happens on my journey home (60 mile drive), but I kept trying to work him for around 20 minutes until I reached one of these locations, and for 20 minutes he replied to everyone except me, if there was ever going to be a chance he would hear me, it was going to at this particular point in the journey, anyway, the upshot is he is now in my log

This is down to luck, time of day etc but we can't ignore the effect of terrain. I know a lot of guys in the UK like to go mobile on the top of a high hill and work the DX, many CBers do this, yet don't fully understand why being on a high hill makes it easier to work the DX, it's obvious to them why it increases the distance line of sight, and why they can work stations in different counties maybe up to 70 miles away or more, but it's the ability to punch their signal to the other side of the World that excites them.

Hope this makes sense and gives you an idea what I'm talking about.

Edit: I've just reread your question and realise I didn't explain the Fresnel zone, however I see by your graphic that you've already googled the subject, however I'm using the Fresnel zone to add in phase reflections to my signal, thus reducing the radiation angle of my signal, the effects of theses zones, and their distance from the antenna affect the signal differently, if I want to reduce the angle of radiation significantly then I'm relying on a Fresnal zone that is a significant distance from me, thousands of feet in fact.

 

[Marconi]

35, I should have used the image that Avanti used in their advertising for the AstroPlane showing what they describe as shadow effect. I did not intend to get into a discussion on the Fresnel zone. I know little to nothing about the subject.

All I did here was find an image on a Fresnel site that I thought might display my idea of blocking RF signals by buildings and other objects on the Earth's surface.

I did this because I'm curious as to how we might expect to benefit when using the counterpoise for 11 meter 1/4 wave antenna that will mostly be mounted well below the typical roof peaks of the average home in US neighborhoods were most of us live. I refer to this problem as ground clutter that interfers with RF signals by attentuation and reflection. I've discussed this idea many times in other threads.

My concern is that the counterpoise idea at 11 meters will produce results similar to an 11 meter ground dependent Bob Tail vertical array antenna that also must be mounted with the vertical 1/4 wave open ends...somewhat close to the Earth.

IMO and experience, the Bob Tail is not very effective at 11 meters, due to its lack of an adequate install height for a short 1/4 wave CB antenna, and its requirement to be installed near the ground.

If the Bob Tail is properly built, at a much lower frequency like the Broadcast idea we've been talking about, then it might work great too.

 

[northern35s]

Ground absorption is a killer at 27MHz, which is one of the reasons why a ground mounted vertical is a bad idea, that and the fact any terrain irregularities, including buildings, is going to kill the signal off pretty quick, certainly for local communication, height is indeed might.

I remember in the early days of UK AM CB radio, my little old Sears Roadtalker 40 struggled to make 8 miles, my 7' firestick was mounted at the back of my parents property at around 10' to the base of the antenna, I had four wire radials coming away at about a 45 degree angle from horizontal, it wasn't much, but as a school kid it was as much as I could muster. The only way I made this particular contact was very late at night, the bands were simply too busy during the day and evening, this was the furthest I'd ever got my signal at the time, it was a revelation.
Fast forward a couple of years, I was in work and had a bit more cash to splash, I had a 1/2WL antenna on the roof of my parents property, probably around 70' high (it was a 4 storey hotel), I could talk to people 20-30 miles away like they were a next door neighbour, happy days

 

[Lil'Yeshua]

Buddy pole antenna

In this vid the guy is using a "counterpoise" wire
Homebrew Buddipole with Modifications - YouTube

 

[HomerBB]

Not a counterpoise. He simply made a vertical dipole.