Your first Amateur radio antenna. Or the antenna you hide in your attic, because of the coming Zombie invasion of course. Whatever your reason for having a wire antenna, whether its your wife, neighbors, HOA ( I hate those), small yard, your renting, your in an apartment or safety reasons or any other reason. Rejoice its a good choice.
The all time favorite HF wire antenna is the half-wavelength, center-fed, dipole. It is easy to build and it performs adequately. The dipole is the reference used to measure the performance of the other antennas. It's the base line. The dipole is a great reference point for amateur radio because you can actually build one (yes you can). And on some of the lower bands, most amateur radio operators will be using these. So you don't have to worry about pile-ups your never going to be able to break. There is also less competition on these bands since most everyone is using the same type of antenna as you... A wire. As well as the lower bands although very noisy at times are very forgiving regarding antennas, so a dipole works just great. Unlike on the upper UHF bands where you need a 11 element plus yagi just to hear anything at any decent distance.
Ham Radio Wire Antennas ......have great benefits:
They are inexpensive to build and make. or they're dozens of pre-made designs built by other amateur operators to choose from.
They are simple to put up in the air. (find a tree and your good to go).
Or if your still worried about Zombies, you can put one in your attic.
You can even really cheap out and feed them with inexpensive feed line...like ladder line! Wow what could be better?
Well sorry there is no Free lunch here either:
Wire antennas often create RF interference and can result in RF at your radio shack, on your TV, in your computer speakers, or even better your neighbors speakers.
The problem is this, the feed line, as well as everything connected it becomes part of the RF radiating system. Many people think that just because you have a 1/2 wave dipole you will be immune to this type of interference. They also are under the misconception that changing the feed line to some mysterious secret length, or use another type of feed line these problems will be eliminated. They won't. This problem usually is worse with a End-Fed antenna that the manufacturer told you doesn't need a counterpoise. Well I can tell you that a counterpoise will be made, whether you know it or not. Something will be used as the counterpoise, most likely its going to be the feedline.
Another issue which involves the above problem is, that you will have increased noise levels. If you have RF leaking out, you have Noise leaking in. Period.
So how can you stop the mass hysteria of chasing RF and interference (you'll never quite find) around your home. There are a couple of things that I would do in my opinion. One: Move the antenna and the feed system as far away as possible away from your house.
Two,Three, Four, etc. Use a good grounding system outside. Use a lightning arrestor outside where you are grounded, use a current Choke at the connection to the antenna, and another one before the feedline gets into the house. Use stock radio power with wires and you will most likely be okay, adding 1000+ watts to any wire system and your asking for a knock on your door. Wires and Circuit boards are soulmates, they want to be together. Your RF leaving your wire is looking for a Circuit board to excite, this is most likely going to be in some of your electronics or more likely your neighbors.
If you are working the lower bands, you do not need alot of power anyway. Mother Nature will take care of you there, and even might lift up her skirt and give you a DX peek a boo every now and then on 160/80 meters, even with your 100 watts and a shortened dipole. If you decided to use a end fed long wire antenna with no counterpoise and 1500+ watts of power, your career as an amateur radio operator will be short. or at the very least expensive from the eventual large FCC fine you'll be paying.
I realize it seems I am going off on amateur radio wire antennas here, but to be honest you should use these practices on any antenna system you have, and you and your wife and neighbors will be alot happier, you never know you might just be invited to their block party even with the 7 element 20 meter Yagi 50 feet above your roof.
OK What is a half wave dipole? How do you design a loop antenna? What is an Off Center fed Dipole? Lets find out.
As mentioned on another page, there are at least 140 varieties of wire antennas and probably dozens more then that. I am not going to go through them all, only the ones I personally have experience with, like everything else on this wa2ooo.com website. And I don't have the room.
1. The Half-wave dipole........... works very well, easy to construct and install, has a figure 8 pattern in books, but closer to omni directional in reality, especially if its not very high. I recommend it highly as a wire antenna. A million words and pages have been devoted to this antenna, so I dont want to repeat others here.
2. The Inverted V....sounds sexy and looks exotic doesn't it? Sorry its just a half wave dipole with the ends (legs) sloping down. Same decent performance as above but even more omni directional.
3. The Loop antenna ( personal fave )... its actually just a one element Cubical Quad. A full wavelength wire bent into the shape of a loop ( delta or square ), you'll enjoy lower noise and better gain then the dipole above. ( just like the cubical quad versus yagi ). Its litterally the same thing, just one element. Usually built as a single band antenna. Can be built for Vertical or Horizontal radiation just like a Quad. Sometimes people call this a Skywire loop, so check if it s bigger then a full wavelength or not.It can be fed with coax and a 2 - 1 balun or use a section of 75 OHM coax to match it. But you really its not that hard to get into the wire length ballpark you'll need. For example 40 meters is not only a ham radio band, its also the length of a 1 wavelength loop at those frequencys. How long is 40 meters? Well 1 meter is 3.28 feet long, so 40 meters is 40 X 3.28 = 131.2 feet long. Or you can do 1005/frequency. However thats a rough guide as wire size, covered or uncovered and a bunch of other things come into practice. If you want to be more precise, as I am sure you would be, you can go here: http://www.66pacific.com/calculators/full-wave-loop-antenna-calculator.aspx.
4.The End-Fed long wire or multiple of 1/2 wave length wire....... They do work, not as good as a loop or a dipole, but sometimes this is the only alternative you can run. make sure you read the RF interference section above at least 31 times before installing one. Okay maybe twice. These are used alot during club station stuff and by portable operators on mini expeditions. What could be simpler? The pattern of these is difficult to predict at best.
5. The Multiband dipole... same as the dipole with other bands (lengths of wire) attached to the feed point, again a Choke is necessary here no exceptions. SWR not always perfect or that good frankly. Keep it as far away from anything else as possible. depending upon the guy who makes it, they work either very good, or fair at best.
6. The G5VR antenna...very popular...cheap... not as efficient as a dipole but gets you on all the bands, with fair performance. SWR also not always as predicted. Lots of good ones for sale and even more poor ones for sale. Its generally 51 feet a side, and fed in the center by twinlead of 29 feet. This is an antenna that can really make you grind your teeth at night. But its Cheap ! Not really a full 10-80 multiband antenna, but often sold as such.
7. The OCFD ( Off Center Fed Dipole ) ... decent SWR on all bands, decent performance on lower bands, lots of little lobes on higher bands, the guy directly south of you might be "S9" while the guy 10 degrees west of him might be "S2". Tough to predict the radiation pattern (sorry Eznec) but a good alternative to the dipole if you prefer. This antenna is usually fed 1/3 from the end, in other words its a 1/3 wire lenght, feed point, followed by 2/3 lenght of wire. The longer the total wire the better.
8. The Carolina Windom... very similar to the OCFD, except it purposely uses the (22 feet or so) feed line for vertical radiation. ( Uh Oh ). works decent but it needs a CHOKE. It also needs precise measurements of everything to get right. Sort of an old school antenna, but still somewhat popular.
9. The Skywire Loop.. similar to the regular loop, just a big large random length of wire in the shape of a loop running either as high as possible or low along the ground for the lower bands. It needs a good tuner at the shack to tune this bad boy. That being said there is alot of wire out there (600+ feet) of Capture Area, to transmit from and hear things on. It works well. if you have 3 or 4 big towers and attach it to each leg of the towers someplace....you have yourself a butt kicking omni directional antenna. Even the lower ones work pretty good. Tune Tune Tune for any band you would like. Mostly used on lower bands.
10. The "I don't care what you say I'm throwing this wire out the window" antenna. Listen enjoy yourself and the bands, watch the RF in the shack, and if QRP is your thing then more power to you. It makes no difference to me what you use, nor should it bother you. Just enjoy the amateur bands. I would comment that throwing a random length of wire out the window will work, but its more a matter of luck then having good practice.
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My experience is with most of these. You will not get much better performance then the Half wave Dipole or Loop antenna. Here comes the flames.......
I personally think these will be the top performers. I have modeled and used many other types ( Rhombics, Double Zepps, Slopers, Doublets, etc. ) and like the crazy Yagi antenna designs that you can come up with, there are hundreds more complicated designs with wire antennas. Now I just dont think they are worth the time and the increase in gain versus one of the above. I can hear it now "I built a capacitive loaded collinear hentenna, that blew away my friends 6 element yagi on a 75 foot tower".
Number one . No you didn't, Number two . Okay great, I don't care. Are there other wire antennas that can give you good SWR, Multiband capability, and High Gain in one direction. I am sure there are. I am not building them, nor will I in the future, but you can! To me the simpler the better.
In fact I'll even help you get started : http://www.n4lcd.com/wireantennas/
