# Tag Info

2

A possibility for their use is suggested by the small "globes" at the free ends of the conductors in the 2nd photo. If this array of conductors was intended for lightning protection, they better would have very sharp tips in order to reduce the flashover voltage appearing at the ends of the conductors. Also, ~vertical conductors would be better ...

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Those are not antennas, but intended to be lightning dissipators. Basically, they are a type of lightning rod. A lightning rod or lightning conductor (UK) is a metal rod mounted on a structure and intended to protect the structure from a lightning strike. If lightning hits the structure, it will preferentially strike the rod and be conducted to ground ...

2

If you were designing a link budget, EIS is the minimum power required at the receiver, assuming the receiver is an ideal isotropic receiver. The EIS encapsulates the effects of both the receiver's sensitivity and antenna system. A link budget might look like this: transmitter power +/- adjustment due to antenna mismatch - transmitter feedline loss + ...

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I think it does not work. In the first place, the shorted quarter wave will present a very high impedance between screen and center conductor so there will be almost no current in the center conductor. Just removing the center conductor and in effect place a metal rod or metal tube with the same outer diameter would give exactly the same function. What you ...

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OK, I've checked 5 or 6 types of traps made of different materials, tuned to the same or slightly different frequencies, tuned right on the band, below the band and above the band. Most of them were not better than the first pair. Tuning above the band doesn't work. Traps made of RG58 coax work best. You get SWR 1:1 on both bands, 320 kHz bandwidth on 20m ...

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I am sure the phasing and proper connection of the coax to the individual dipoles will get you a pretty good hemispherical CP pattern. It is easy to get confused when connecting the coax to the dipole.

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Yes, that's correct. If the elements are isotropic then as you've written it, $G=1$ And the effective aperture increases by $N$. Of course this new aperture is only effective in the direction of the peak(s) of the response, elsewhere it will be less. And this assumes that the elements are far enough apart that there's no coupling between them.

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How about a J pole with decoupling below the feed point.

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There should be some difference in efficiency, on the basis that the vertical portion of an inverted-L is "pure radiator", whereas the horizontal portion functions partially as a capacity hat (but not entirely — it also radiates). You can see this in the fact that an inverted-L has a lower feedpoint impedance than a quarter-wave built for the same ...

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Below is the result of a NEC4.2 comparison of the radiation patterns & gains of the two configurations of radiators, with other things the same.

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W8JI has some measurements, and the worst case loss he found for two traps in a dipole was 1.6 dB. These were coaxial traps, operated at their resonant frequency, which is both the worst way to tune a trap, and the worst kind of trap. The losses are indeed mostly resistive losses, but not just because there is more metal. Losses are highest at resonance ...

2

A trap is usually a notch filter, designed to stop frequencies within a certain band from passing. The theory is that if you have a wire dipole that is electrically tuned for 20m, and then you put a pair of traps in there to ‘cut the antenna short’ when a signal at 21MHz is presented, you can effectively have an antenna that is resonant on 20m and 15m. This ...

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I've never seen a balun design like this and and I'm not entirely certain it works. But if it does, here's how I think it could work: As you say, a shorted quarter-wave stub appears like an open circuit. So the stub is a parallel open circuit to the differential mode: it has no effect. To the common-mode, the stub and the parallel section of feedline make a ...

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Beverage antennas are extremely inefficient. For receive applications this is not much of a problem, but for transmitting it's a big problem. As such, trying to match a transmitter to such an antenna is a futile exercise. At best, what you would achieve would not be much better than a dummy load. Most of your transmitter power will just make warm soil. You ...

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