8

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 ...


6

The number of horizontal radial wires used in an elevated "counterpoise" can be far fewer than the 120 buried wires used by most AM broadcasters, and the even fewer numbers of buried wires often used with vertical monopoles, inverted Ls etc by amateur radio operators. Several AM broadcast stations use 3 or 4 pairs of λ/4, co-linear, horizontal radial wires ...


5

The purpose of the ground radials isn’t to ground the counterpoise. The purpose of a dense field of radials is to emulate as much as possible a perfect mirror surface, so that, to the far field, the vertical monopole seems to have a mirror image half that makes the monopole seem more like a full size vertical dipole, with a pattern maxima orthogonal to the ...


5

The purpose of the counterpoise is to provide an efficient means of conducting the return RF current of the antenna. In the absence of an efficient counterpoise, the current will return through the lossy earth or poorly quantified paths such as coaxial cable shields. An efficient counterpoise will carry the same current as the primary radiating element. A ...


5

Here is an analysis of a vertical, 1/2 wavelength, 2 meter dipole suspended at various heights above ground: As you can see, as you raise the bottom end of the antenna from near ground level up to about 7 wavelengths, the gain increases. At the same time, the elevation angle of the maximum gain decreases (becomes closer to the horizon). As you continue to ...


4

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. ...


3

A dipole antenna does not require a connection to an "r-f ground" reference, either in the form of a ground rod or a set of buried radials. Its radiation efficiency typically is ~95% or more without it. OTOH, a vertical monopole does require a path to an r-f ground reference, because that path provides the 2nd terminal of the antenna system, which ...


3

A layer of corrosion between two metals forms a capacitor (or, sometimes, a diode). RF will go through it better than DC, because RF can go through capacitors and DC can't. However, that doesn't mean it's an acceptable substitute for metal-to-metal contact, because the antenna wasn't designed to have an impedance (capacitance) there! In your specific case, ...


3

There are a lot of variables involved in calculating the voltage on an antenna. If you require an accurate answer, the solution is to model or empirically measure the particular antenna in question. But for a very rough estimate, a 1/4 wave "counterpoise wire" is effectively one leg of a half-wave dipole, so you can treat it as such to get some number. In ...


3

With only three radials, the wire you use is probably not very relevant. Although a smaller wire has a higher resistance and thus loss, with only three radials directly on the ground your losses will still be dominated by the resistive loss of the soil. As a rule of thumb, a good ground requires at least 16 radials. It's not critical that they be exactly a ...


3

If you run a wire up in your attic, all other conductors such as ducting, house wiring, gutters, and so on are part of your antenna system. You want to avoid near-field capacitive coupling as your losses will definitely go up in that case. Therefore, a wire antenna close to other conductors that run parallel to the antenna conductor is not good. I am a ...


3

The voltage is high near the end of any dipole. If you locate the bottom end of a vertical dipole at --and especially below!-- the ground, you are greatly increasing the losses. There is really no specific distance from the earth to the bottom end of the dipole to the earth, above which is good and below which is bad. It just needs to be up and away from ...


3

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 ...


2

Can you elevate the radials? Two or three properly installed elevated radials can be just as effective as 120 on the ground! By properly installed, I mean that they should be roughly 10 feet high and have an effective common-mode choke on the coax right at the junction of the radials and coax shield. This junction MUST NOT BE GROUNDED. Try and make the ...


2

The downside of having your counterpoise in the shack is that it will be much closer to all the noise in your shack: your computers, powerlines, and so on. The counterpoise, and everything between it and the antenna, is every bit as much of the receiving structure as the "antenna". Also there will be stronger RF fields near your shack. This may or may not ...


2

Here is another answer on this site about buried vs. elevated radials.


2

The Hustler web site says: "For optimal performance, radial wires should be used." Somewhere else, there is a recommendation for sets of 3 tuned radials per band on which you plan to operate. A short metal pole in the ground does not act as a proper RF counterpose for HF bands, nor does it prevent ground losses, and will very likely not allow the best ...


2

Surely a 1m copper stake provides better ground connectivity for a vertical dipole? What really matters is conductivity. Current doesn't just go in the ground rod and then it's done. It has to flow through the surrounding soil. Soil isn't a very good conductor: (68.2 kΩ, says the display) Now imagine how much lower this resistance would be with a copper ...


2

Because the radials act as ground, and they're better at it than actual ground. Ground (as in: dirt) isn't a great conductor. A couple laid out good conductors hence work much better as ground plane than well-connected earth. For RF, a good connection to ground potential isn't necessary – what's necessary is that there's a large plane that conducts.


1

Below is a graphic comparing some of the operational parameters of ground-mounted and elevated vertical radiators for the 40-meter band. Their performance when installed at sites with relatively poor Earth conductivity is fairly similar.


1

As a start, below is a NEC analysis of the system described in the OP. The horizontal radials lie along the +Y or the + and -Y axes.


1

Either elevated radials, or radials lying on the ground or buried just below the surface can work just fine. The difference usually comes down to what's more convenient to install. I would not recommend a folded counterpoise, or any other kind of counterpoise which is not simply a straight wire unless you are constrained by space. Elevated radials have the ...


1

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. ...


1

You could just use the ducting in lieu of the wire. Anything conductive makes an antenna to some degree. For example, gutters. I wouldn't suggest putting more than 10W into your ducting unless you want to find out how your air handler deals with RF current, but the same advice would apply to a wire running in close proximity to your ductwork also. If you do ...


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