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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3Maybe 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. – user10489 Feb 18 '22 at 01:37
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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. – NonYaBidnezz Feb 18 '22 at 01:44
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2Point 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. – user10489 Feb 18 '22 at 05:48
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1Yep, "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). – Marcus Müller Feb 18 '22 at 13:36
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This Q prompted me to do a basic web search and it turns out that the received wisdom (or possibly, research) is that multi-half-wavelength unterminated end-fed long wires _are_ somewhat direction. some even describe them as a multiple number of half-wave dipoles in one antenna. An antenna where you encourage standing waves. Huh. Anyway, the info is out there if you do a web search. – Feb 18 '22 at 16:21
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@jdv The main lobe of a one-wavelength Beverage has a 3 dB beamwidth of 90°. – Mike Waters Feb 18 '22 at 22:36
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Where did you hear this? A Google search for *808.28 feet long antenna* returned no search results. – Mike Waters Feb 18 '22 at 22:48
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1@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.) – Feb 18 '22 at 22:50
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@jdv I see what you mean. But a 10' wire parallel with the ground has a surge impedance of about 450 ohms. Using a suitable un-un (1:6.25) to isolate the coax from the wire, I found no standing waves of any significance. Pretty sure that I also modeled that with [EZNEC 5.0 +](https://eznec.com). – Mike Waters Feb 18 '22 at 22:58
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I think the idea is a wire 3-5 1/2 wavelengths long. Hence, working with hundreds of metres of wire. – Feb 19 '22 at 20:00
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I wonder if the OP is asking about this sort of antenna?https://youtu.be/EtEBxY8TvuE?t=471 Definite similarities to a Beverage but appears to be further above ground and described in terms of **transmission** gain (resistor losses simply accepted?). – natevw - AF7TB Jul 07 '22 at 21:55
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Video goes on to mention further extension of that concept into a Rhombic (https://en.wikipedia.org/wiki/Rhombic_antenna / https://qrznow.com/the-mighty-rhombic-the-king-of-antennas/) design as well. – natevw - AF7TB Jul 07 '22 at 22:00
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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.
Mike Waters
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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 !
Andrew
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