10 votes

Can a 1:1 transformer be used as a protection from static electricity?

A transformer can help and could also make things worse. I have some bad experience with this. The way that a radio is damaged by static is simple: Something charges up to a high voltage, and then ...
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  • 8,235
8 votes
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Tuning/trimming a ground plane antenna

My trick is instead of cutting, rather extend the whip first, and see if the SWR gets better or worse. Extend it 1/2" with a bit of wire wrapped around it and sticking out. If the SWR gets better, ...
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7 votes
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What is the attraction of vertical antennas for HF?

Cribbing a few quotes from answers to related questions, here's a start. From https://ham.stackexchange.com/a/195/1362: The primary advantages of vertical antennas are that they are ...
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7 votes
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When and why does the size of a ground plane or radials matter?

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....
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7 votes
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Radials on a vertical, spread out evenly or not?

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 ...
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7 votes
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calculating all specifics for a 5/8 antenna

I congratulate you on your interest in working out the design issues from the ground up. Understanding the theoretical and comparing this to the field results is the beginning of a life long enjoyment ...
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6 votes

Marine VHF whip antennae - what are they?

Without having one of these antennas to disassemble (perhaps destructively), I can't tell you exactly how they are constructed. But maybe I can address some of your underlying concerns. Firstly, ...
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6 votes
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How to calculate/estimate the effect of having conductive material nearby an antenna

In your particular case, I'd note 2 things: The aluminium is directly above the whip, where the antenna's fields are the weakest. Aluminium is a good conductor, so unless there is something about it ...
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6 votes

How Does the Performance of Elevated Radials Differ from That of Buried Radials?

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 ...
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  • 2,882
6 votes
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Stabilization of an antenna pole with anchoring cables

What you have is a basic civil engineering problem. You might calculate a sheer and moment diagram, look up all the material properties, and calculate the failure points of all the components. In the ...
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6 votes

Radial length for vertical antennas?

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 ...
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6 votes
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Vertical Antennas

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 ...
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6 votes

Why are many ground radials preferable to a single ground stake buried 1m deep?

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 ...
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  • 12.5k
6 votes

cut or lengthen to reduce swr on vertical wire antenna

If you're only measuring SWR at one frequency, or in a narrow range like the ham bands, you won't know until you cut it. Mount the antenna in its final location as the SWR and resonant frequency will ...
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5 votes

Tuning/trimming a ground plane antenna

If you take SWR measurements at a range of frequencies and plot them (or just watch the SWR reading as you change frequency), you should get a graph with one or more valleys of low SWR. Ideally, if ...
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5 votes

Using two short mobile HF antennas to make a vertical dipole

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 ...
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5 votes
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Can a vertical antenna be used for NVIS?

Knowing that 1/4λ verticals are known in VHF/UHF applications to have nearly isotropic patterns This is not a valid assertion. A UHF/VHF vertical antenna has > 0 dBi gain (more succinctly a ...
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  • 18.2k
5 votes

How Does Earth Conductivity Affect the "Takeoff Angle" of a Vertical Monopole?

A common belief is that Earth conductivity mostly affects the "takeoff angle" of a vertical monopole. However the NEC4.2 study below shows that the shape of the radiation patterns is quite similar ...
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5 votes
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How low can a vertical dipole be mounted?

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 ...
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  • 18.2k
5 votes

Antenna suggestions for 160m band in smallish yard?

Almost any 160 meter antenna is a compromise. With limited space or budget, the compromise tends to be larger. At first glance, a dipole that is shortened by loading coils might appear quite ...
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5 votes

Are Elevated Radials Necessary for Elevated, 5/8-wave "Ground-Plane" Antennas?

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 ...
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  • 2,882
5 votes

Give vertical antenna directional gain?

Sure, that can work. Here's a monopole yagi I designed: Photo: Alaris Antennas MONO-A0005. It's a half-yagi for remote control of a mine locomotive, improving the control range by firing one way ...
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  • 8,235
5 votes

Multiband vertical antenna not working as expected

It may very well be that the open contacts are arcing, and I'm betting that's what is happening. Here are some possible solutions. How about using different relays that have less tendency to arc: ...
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  • 7,544
5 votes

Colinear Vhf antenna

The ideal dipole antenna is roughly a half wave long. A monopole is half of that, with the other half in the conductive surface below the monopole. The colinear antenna is a series of stacked and ...
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  • 4,258
5 votes
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Can a 1:1 transformer be used as a protection from static electricity?

Assuming that power losses in the transformer are acceptable, and that it's placed after 1:1 current balun (which eliminates common-mode current), is there any reason why it might be a poor solution? ...
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5 votes
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Why are many ground radials preferable to a single ground stake buried 1m deep?

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 ...
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  • 2,882
5 votes

Is the Boom Strictly Necessary in a Vertical Dipole?

If you don't route the feed line away from a center-fed dipole antenna at 90 degrees, it will be in an unbalanced RF field, and thus will couple to the unbalanced RF field, to some degree, even with a ...
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  • 12.5k
5 votes

Can coax be run through the center of a radiating element without currents being induced on the coax shield?

That is a great idea. In fact antennas of this design are quite common, and you probably have a much smaller antenna of similar construction on your Wi-Fi router: Effectively, the lower dipole ...
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4 votes
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How to calculate or estimate surface area of required ground plane for a mobile antenna?

What are the rules of thumb for getting ground plane dimensions for a mobile antenna beyond "the bigger, the better"? There isn't one. An monopole antenna does not reach ideal performance until the ...
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4 votes
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2 Meter horizontal or vertical dipole polarization?

For VHF, choice of polarization is not up to your desired radiation pattern, but who you want to be able to communicate with. In HF, the ionosphere causes random rotation of your signal's polarization,...
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