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So multiples (by 3x-5x) of full wave lengths long? It's my understanding that you can build an antenna that is 802.28 feet long and it's naturally resonant WITH GAIN on all the usual Field Day frequencies? I'm hunting more information on this. We have an awesome Field Day location in a national forest with space to burn. :-)

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    $\begingroup$ Maybe you are looking for "beverage antenna" ? Note that an antenna with gain also is directional, and unless you can aim it too, you probably don't want that for field day. Aiming a 800 foot long antenna might be a little extra exciting. $\endgroup$
    – user10489
    Feb 18 at 1:37
  • $\begingroup$ According to my Elmer, (20 years with the Airforce as a Radio guy) it's quadra - directional so maybe not much reason to move it? The fact that we aren't sure is why we are looking for someone who has had more contact with it. According to my Elmer, this was a common antenna type many years ago for commercial applications. $\endgroup$ Feb 18 at 1:44
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    $\begingroup$ Point being, if you use a directional antenna aimed in one direction at field day, unless you are already on the edge of the country, you're going to miss a lot. $\endgroup$
    – user10489
    Feb 18 at 5:48
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    $\begingroup$ Yep, "gain" says "unlike a perfect isotropic radiator, I don't divide my transmit power identically in all directions; I prefer some directions"; inherently, other directions get less of the power. So, antennas with gains only help when you have a way of pointing them in the direction you know your communication partner is (RX is the same as TX, passive antennas are reciprocal). $\endgroup$ Feb 18 at 13:36
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    $\begingroup$ @MikeWaters the experiments people are doing is on multi-half-wavelength long end-fed wires, unterminated so you get lots of standing waves. I literally searched for "end-fed resonant long wire antenna" or something. And, yes, apparently it used to be quite the thing if you had the room. (Though, "resonant" in this case might be playing fast and loose with the term.) $\endgroup$
    – user21417
    Feb 18 at 22:50

2 Answers 2

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It's my understanding that you can build an antenna that is 802.28 feet long and it's naturally resonant WITH GAIN on all the usual Field Day frequencies?

Not so. What you heard about was probably a Beverage antenna.

Beverage antennas are commonly terminated with a resistor equal to the surge impedance of the wire. That makes them non-resonant. However, they are very useful for receiving over a very wide range of frequencies.

They have negative gain, at least 8 db below an isotropic (non-directional) antenna. Although lossy, they often are superior to a dipole for DX, even for transmitting.

As others have stated, you must point it in the desired direction.

You can also dispense with the far-end termination resistor. In that case, it will be bi-directional. You will also receive signals off the feed end about 6 dB down from the far end.

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Long wire antennas are resonant at odd and even multiples of a half wave length, and the actual length of the half wave depends directly on the frequency of operation as per this formula :

Wavelength (m) = 300,000,000 / frequency (Hz)

Your antenna with length 802.28 feet which is about 20 meters would be approximately resonant on the 10, 20 and 40 meter amateur bands, it being 2 wavelengths long on 10 m, 1 wavelength long on 20 m, and half a wavelength long on 40 m.

The feed point impedance of your long wire antenna needs to match that of the transmission line and radio equipment you are using. Many ham radio operators confuse impedance with resonance. An antenna can be resonant but have an impedance which doesn't match the impedance of the transmission line and radio equipment. Resonance depends entirely upon the antenna dimensions and is affected by nearby objects, whereas impedance depends on the antenna dimensions and on where along the antenna length the feed point is positioned.

Dipole antennas for example, which are like a long wire but with the feed point in the center, have a high feed point impedance at even multiples of half a wave length and a low impedance at odd multiples of half a wave length.

Despite all this, any antenna will work at least a bit, you can use any length of long wire with an antenna tuner to match the antenna impedance to that of your equipment, and it will probably work well enough for the purposes of your field day.

Note that long wire antennas and dipoles have some gain in different directions, which increases as the length increases, but the gain is not very high and is probably not going to make much difference for your purposes.

If you need further reading, i suggest you steer clear of ARRL publications as these are hard to read and confusing, i have found the following books very good if you are interested.

  • Antennas - Alexander Shure
  • Antenna Theory Analysis and Design Fourth Edition - Constantine A. Balanis

Hope that helps !

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