# Tag Info

16

An ideal vertical doesn't have radials: it's half a dipole sitting upon a perfectly conductive, infinite plane. Under these idealized conditions, its radiation pattern is identical to a dipole's radiation pattern that's been sliced in half (like a bagel), and the vertical's feedpoint impedance is exactly half that of a dipole. When the plane under the ...

7

The purpose of the radials is to increase the effective ground conductivity, thus reducing losses. As you propose to have 16 radials but in four groups, I'd expect the efficiency to be somewhere between 4 radials and 16 radials evenly spaced. That said, if you need to do this to work around some obstacle, then by all means do it. You can also make the ...

6

Perhaps consider that the objective of the ground plane is to present a low impedance. At the feedpoint, the hope is to have all the current go into the antenna, and none of it on the coax common-mode. The lower the impedance of the ground plane, the less current will be on the coax common-mode due to its relatively high impedance. If the ground plane ...

6

Elevated radials not equal to ground plane A common misconception is elevated radials (as counterpoise) perform the role of "ground plane" in an antenna system including dominating the far field effects from real ground over which the antenna resides. Radials perform two roles: a conductive path for the inner shield currents and a method to ensure the ...

6

Rule of thumb: if the radials are elevated, at least two resonant radials for each band. If the radials are buried or lying on the surface, at least 16 radials, each at least a 1/4 wavelength at the lowest operating frequency, and don't worry about resonance: just get as much wire in the ground as you can. More and/or longer is better. The objective of any ...

6

First: do you know about pskreporter? You're definitely getting heard, including one spot on 40m from New Zealand. Sometimes FT8 takes some patience, and it seems like no one wants to come back to you for long periods of time, but pskreporter can at least provide some reassurance that your equipment and the ionosphere are actually in working order. That ...

5

Elevated radials are required in order to increase/optimise the radiation possible from any such elevated "GP" monopole or whip antenna. If the elevated radials are symmetrically arranged and lie in the horizontal plane, then their net far-field radiation is zero. However the r-f current at the common point of those radials is not zero — it is the same as ...

5

Larger wire will have less resistance. However, the resistance of the radials in either case is negligible compared to the soil resistance, so I wouldn't worry about it. Longevity would be my concern. Commercial broadcast towers use 10 gauge bare wire. Anecdotally, there are plenty of amateurs happily using 18 gauge wire. Corrosion depends on many factors. ...

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 ...

5

To begin the discussion, it is helpful to understand the effects of shortening any antenna to a length below resonance. In all cases, the directivity of the antenna is reduced but this tends to be a fairly uniform reduction regardless of how much shortening occurs. The reduction in length also reduces the radiation resistance of the antenna. This is ...

4

The effects of using unequal length buried radials on the radiation patterns of a monopole are not very significant, as shown by the NEC4.2 analysis below.

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

People can and do use a pair of mobile antennas to make shortened dipoles. A "hamstick dipole" is one example. One application for such an antenna is in a mobile station which for whatever reason requires a horizontal polarization. It's also a quick way to make a small antenna where space would not allow for a full-sized dipole, such as an attic antenna, ...

3

Developing this comment of W2ASC (above): But, given the fact that radials are effective even when buried in a few inches of soil, my assumption was (and still is) that whatever difference exists between the two insulation types is - for all practical purposes - negligible. So, my question is probably a bit academic. I still believe my initial assumption was ...

3

Sure it will work. Metal wire is metal wire. The electrons don't care about the packaging. 24 gauge wire is thin enough you might be concerned about the resistance of the wires, which will decrease antenna efficiency. Use some RF resistance calculator to get some estimate of the resistance, and remember if you have 16 radials, then the effective resistance ...

3

Below is a NEC4.2 comparison of the v-plane patterns of a 1/4-wave ground plane antenna mounted 5m above level Earth and using 4 x 1/4-wave, horizontal radials, with / without a coax transmission line having the OD of the shield "grounded" to the Earth. Two observations: The 4 x 1/4-wave horizontal conductors do not effectively decouple the transmission ...

3

VERTICAL MONOPOLE, EARTH, and BURIED RADIALS as FACTORS in ANTENNA SYSTEM RADIATION EFFICIENCY Considerations: The components shown in the graphic below, and the soil where they are located/buried are elements of the complete antenna system. R-F currents flowing on/in the earth within a radius of 1/2 wavelength from the monopole as a result of its ...

3

The information below is extracted from the "benchmark" 1937 I.R.E. paper* of Brown, Lewis & Epstein of RCA Laboratories, and is based on their accurately measured data for these systems. IMO, the outlined and underlined text at the bottom of this clip is worth remembering, and deserves greater access/acceptance. *Proceedings of the Institute of Radio ...

3

Below are NEC4.2 analyses showing the intrinsic, free space radiation patterns of (1) a ground plane antenna having two pairs of co-linear, λ/4, horizontal radials spaced at ±90°, and (2) a comparison of the free space elevation pattern of the ground plane antenna to that of a λ/2, center-fed dipole. The λ/2 dipole has about 0.7dB more gain than the λ/4 ...

3

As long as the radials are symetrical it will make no noticable difference. A single radial opposite the other half of a dipole or 2 radials opposite each other will yield a reasonable pattern. The key is symetry so that the radiation pattern is not distorted. Any number of radials will do, even odd numbers, if kept symetrical. Most people agree that more ...

3

Will this significantly change the omnidirectional nature of this antenna? Yes. For 270 degrees of azimuth, you have no ground plane. Or another way of looking at it: you are missing 3/4ths of your radials. There will still be some radiation in every direction, but you may find that there is significantly less radiation in the direction where you have no ...

2

In broadcast AM radio it is standard practice to use quarter-wave towers (because half-wave towers are expensive and more of a maintenance headache). These towers require a ground plane to reflect the signal in such a way that it virtually provides an image of the rest of the half-wave that allows for lowest voltage and highest current at the feedpoint. (...

2

Radials are grounded to the feedpoint. For instance, the shield of the coax feeding the quarter-wave antenna. For AM radio broadcasting stations, there are radials every 3 degrees (120 of them) and they are generally buried (enough so you can still mow the lawn above them), so they are at ground potential their entire length. If the radials are not ...

2

The radials are not connected to the earth. Here's a photo of a ground plane antenna. They are connected together as shown to the coax shield. This shield should be connected to the common on the board that can serve as an RF ground.

2

You can remove them and instead attach the shield of the transmission line to the actual roof! It will make a great ground-plane, probably much better than the radials that are currently attached. Alternatively, connecting a copper mesh will work too. You will definitely want something though, as you'll be giving up some power and efficiency if you just ...

2

Below is a NEC4.2 study comparing the fields radiated by an eighth-wave, series-fed vertical monopole driven against sets of thirty buried radials of 1/4 and 1/8 wavelength (other things equal). The X axis shows field intensity (E), and the Y axis shows elevation (Z) above a flat Earth ground plane, at a horizontal distance of 100 meters from the base of ...

2

Infinitely long radials are ideal. So to directly answer your question: no, there is no such thing as "too long". However, infinitely long radials work because the current in the radials approaches zero as distance from the base approaches infinity. At some point the current is negligible, so truncating the radial at any point makes no significant ...

2

You might look into a noise cancelling device. The principle of operation on this is to use a second antenna to 1) capture the same noise but phase shifted 180º and 2) mix/add to the primary antenna's signal to leave just the desired signal. The second antenna doesn't need to be huge or effective... in fact, if it's not very sensitive and the only thing it ...

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

Thanks for joining us on Ham.SE! Insulation on wires will affect performance if they are part of the antenna's system of resonance. Just as with coaxial cable, adding insulation to a wire decreases the speed at which electromagnetic effects propagate: $$\lambda=\frac{vc}{f}$$ where $v$ is the velocity factor of the insulation and is less than or equal to ...

Only top voted, non community-wiki answers of a minimum length are eligible