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I was searching for DIY end-fed antenna.
Some of the articles I found say that for a 1/2 wavelength end-fed I need a "small to no counterpoise" (with a lambda*0.05 m counterpoise), but some other articles say that I need "a good RF ground in close proximity to the end of the antenna".

Initially, I thought that a good RF ground is required for a random wire antenna but not for 1/2 wavelength one. But I just got an answer here saying that it is needed.

What is the truth? What type of end-fed requires a "small to zero counterpoise"?

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No, it is not needed, but it can improve the antenna system.

An EFHW is simply a half-wave length of wire and a matching device, and that's it. Counterpoises are commonly added to shunt common mode reflections when operating outside of the wire's resonant frequency to avoid RFI issues ("RF in the shack"). An RF ground (defined here as either very conductive ground, or a radial or grid system of wires beneath the antenna with a radius at least 1/4λ from the antenna center) isn't required.

However, that ground system improves the conductivity of the ground, which can have a positive effect on the radiation pattern, but little to no beneficial effect on the VSWR. It can also serve the purpose of the counterpoise if the ground side (shield) of the coax is connected to it near the antenna's feedpoint, but that's far more effort than it's worth.

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An end-fed half-wave operates on a principle that, for lack of a better name, I will call "voodoo".

If you look at the standing wave on a half-wave element in isolation, you see that the center is the point of highest current and lowest voltage (therefore lowest impedance), and the ends are the points of highest voltage and zero current (therefore infinite impedance). The factors that make the impedance less than infinite, and therefore make it possible to feed the antenna at all, are the same parasitic/environmental factors that we usually ignore in a quick-and-dirty analysis of an antenna because they're unpredictable and hard to quantify — things like stray capacitance with nearby objects, losses in the matching system, the fact that things we model as zero size actually have physical extent, and (especially) interaction with the feedline. A great many end-fed systems are dependent on feedline radiation to really work; since feedline radiation is generally a cause of RFI problems, operators try to use chokes to raise the common-mode impedance of their feedline, only to find that the feed impedance of their antenna has gone up as well, and they can no longer get a good match.

These issues lead to all sorts of creative solutions to try to make end-feds behave, and one of the simplest ways to make an end-fed behave less like an end-fed and more like a dipole is to make it less of an end-fed and more of a dipole. By adding a "counterpoise" to an end-fed, you are adding some kind of an element on the "other side" of the feedpoint. In other words, you're moving the feedpoint away from the end. In other other words, you've turned your end-fed into something more like a (very) off-center fed dipole. The current at this new feedpoint is greater, the impedance is merely large, and with proper matching, power will actually want to go into the antenna. This makes the antenna's behavior more predictable based on its own characteristics, and less sensitive to where it's placed, how it's fed, and other "voodoo" factors.

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  • $\begingroup$ So, yes I can add a 0.05 wavelength counterpoise and a choke? (and decrease main wire length by 0.05)? And this will turn my "end-fed" to "not-actualy-end fed". Can I make my antenna in L shape, when bottom line is a counterpoise or it should look like a normal dipole - straight? $\endgroup$ – Hose Dias Dec 11 '18 at 11:40
  • $\begingroup$ I mean a 7-like shape - top part of 7 will be across my balcony and "leg" or "main wire" will go down to the tree. (I think I need to register a second question, and I will if answer to my first question is yes)/ $\endgroup$ – Hose Dias Dec 11 '18 at 11:46
  • $\begingroup$ @HoseDias yes, that sounds alright. Don't go chopping off the wire immediately, though — adding the angle reduces electrical length, so you're going to want to tune empirically. $\endgroup$ – hobbs - KC2G Dec 11 '18 at 21:48
  • $\begingroup$ The voodoo principle? Really? As a point of information a half-wave antenna is a dipole regardless where it's fed... by industry definition of a dipole antenna. $\endgroup$ – JSH Jun 14 at 17:30
  • $\begingroup$ @JSH That depends on who you ask. Although the IEEE agrees with you, people like Terman, Jasick, and Krause differed. ;-) $\endgroup$ – Mike Waters Jun 14 at 18:02
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The EFHW (end fed half wave) needs to be classified as a specific case of the class of end fed wire antennas. The name is even a bit of a misnomer since the EFHW is often operated on multiple bands and therefore is no longer a half wave antenna. And due to the implementation details, the antenna is in fact often not even a half wave at its design frequency.

But let's start with the general situation of a half wavelength long piece of wire. As long as it remains a half wavelength long, the gain and radiation pattern of the antenna is the same even if we feed this half wave wire at various points along its length. At nearly every point that we choose to feed it, the antenna will not be resonant - that is to say at nearly every feedpoint, there will be reactance. Technically speaking, even a center fed half wave antenna is not resonant - we shorten it slightly from a true half wavelength in order to make it resonant when center fed.

When you feed a half wave antenna in its center, the antenna feedpoint is balanced - that is to say that each half of the antenna has the same impedance and so the same current would naturally flow into each half of the dipole. At any other feedpoint, the two parts of the antenna exhibit different impedances which results in different effective currents in the two sections. This can present challenges as it relates to the feed system. The corrective action is often a current balun that "forces" the same current into each part of the antenna in an effort to reduce the inevitable common mode current on the feedline.

The extreme case of imbalance when feeding a half wave antenna occurs when it is fed from the end. The impedance at the end of the antenna will be quite high - typically 5,000 ohms or more. To tame this high impedance, an impedance transformer of at least 9:1 and as high as 49:1 is often used. This transformer is a simple autotransformer so it can do nothing to reduce common mode current on the feedline. It also tends to be quite lossy when used over a wide frequency range. This helps improve the SWR due to the lower Q but this comes at the expense of reducing the efficiency, and thus gain, of the antenna.

What is often overlooked in an end fed antenna design is that the current that is present on the half wave element needs a method of returning to the transmitter in order to allow the antenna to efficiently radiate. There are erroneous claims on the Internet that the autotransformer somehow provides this path but that is simply not true. The autotransformer provides a return path for some of the current on the feedline (in the form of a reflection) but not for the current on the antenna.

Yet we know that an EFHW "works" to some degree as many people have success with this style of antenna - so where is the path for the return current? The answer is highly dependent on the installation. In most cases, the external braid of the coax provides the return path. When this happens, the braid is actually part of the radiating antenna. So it transpires in this case that the claimed half wave antenna is no longer a half wave at all! This also means that the antenna pattern is likely not what would be suggested by the spacial orientation of its half wavelength piece of wire.

In other installations, if the shield connection of the autotransformer is directly grounded to an earth ground system, the return path will largely be through the lossy earth (although some shield current can still exist). Due to the lossy earth, the antenna system efficiency, and therefore gain, is reduced.

The third installation variation is to install counterpoise wires that drop from the elevated transformer down to the ground and then run along the ground. In this case, these wires will typically also form part of the radiating antenna but at least a good part of the return current comes via these wires instead of the lossy earth.

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There's confusion about counterpoise because there's two kinds of end fed antennas. Both are multi-band, but different approaches to achieve this.

The first kind is deliberately non-resonant, uses a 9:1 unun and requires a tuner. It may require a good tuner if you want to work the low bands on a short wire. Some suggest a counterpoise of .05 or .1. Common lengths are 44' 53' etc.

The second kind is EFHW which is half wave resonant on the lowest band but is also resonant on all harmonics. This requires a 49:1 unun or similar and if built and installed right, should not require a tuner, except to cover all of 80m. If you use a 0.05 counterpoise here, you will likely need a tuner. With my installation, a ground rod was excellent to sufficient for most bands and 2 rods were slightly better for SWR. You may try adding additional .25 counterpoise wires for problem bands if you really don't want to use a tuner. I've noticed that adding to the counterpoise system always seems to help and never hurts.

A DC ground is desirable for lighting and static electricity, but not required if your counterpoise wire(s) is effective. Though ground rods are forbidden with 1/4 wave verticals due to resistance, they're not a problem for EFHW since much less current flows through the rod than when driving a 1/4 wave. For non-resonant wires using 9:1 unun, ground losses will be greater than EFHW and will become a problem when trying to load up lower bands on short wires.

For either antenna, I recommend using a common mode filter at the antenna and use a separate counterpoise system instead of the coax shield.

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I was searching for DIY end fed antenna.

end-fed: A monopole?

"a good RF ground in close proximity to antenna end".

That's true for a ¼ wavelength monopole, where the ground acts as "mirror" and lets the antenna behave like a half-wavelength dipole.

You don't want a full-wavelength dipole (unless you like grating lobes...), so, for a half-wavelength antenna, you avoid the mirror ground.

You wouldn't end-feed a half-wavelength antenna. You would normally divide it in its middle and make a half-wave dipole out of it, which is a good antenna.

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    $\begingroup$ a half-wave monopole is twice as long as a ¼ wave monopole, and exactly the same size as a 1/2 wave dipole. Whatever you're doing, a half-wave monopole probably isn't the right thing. $\endgroup$ – Marcus Müller Dec 10 '18 at 15:39
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    $\begingroup$ There's been two downvotes, which is democratically fine, but I'd like to know where I was wrong! $\endgroup$ – Marcus Müller Dec 10 '18 at 16:26
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    $\begingroup$ An end fed half wave antenna is a half-wave length of wire fed from the end; It's exactly like a standard dipole, just not fed from the center. It's not a monopole, and it has the same radiation pattern as a dipole. It's just that the impedance at the end is very high, requiring something like a 9:1 balun to bring it closer to the range of an autotuner. That said, putting the end of the antenna very close to the ground, as you do, certainly does quite a number to the radiation pattern. $\endgroup$ – Sterling N0SSC Dec 10 '18 at 17:46
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    $\begingroup$ I think that the problem is that you're mostly insisting on particular terminology without actually explaining the situation to people not already familiar with the point you're trying to make. $\endgroup$ – Kevin Reid AG6YO Dec 10 '18 at 17:47
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    $\begingroup$ @HoseDias Those articles are using incorrect terminology. An end-fed antenna is not a dipole. Also, welcome to ham.stackexchange.com! :-) $\endgroup$ – Mike Waters Dec 10 '18 at 17:54

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