HORIZONTAL LOOP ANTENNA CONSTRUCTION
The Horizontal Loop, also known as the Loop Skywire Antenna, is an old but very effective design. Although this design has been around for a long time, it is only gaining popularity now due to the recent improvement in high power antenna tuners. The main purpose of constructing this omni directional antenna is to provide a multi band antenna which performs well from the lowest frequency band for which it is designed, all the way through 10 meters. It will usually even work well on 6 meters if your tuner will handle that band. It must be understood that an antenna tuner (trans match) will be necessary for use as a multi - bander, as well as the use of 450 ohm ladder (window) line as the feed line. You will of course need a 4:1 Balun near your tuner, or a tuner with a built in Balun to feed your rig’s unbalanced antenna connector.
How long to make it. To cut the antenna wire length to resonance we use the formula Length (in feet) = 1005 divided by frequency (in MHz). We must subtract 4% of the total full wave length if we are using insulated wire. Example : For a 160 meter loop, 1005 divided by 1.800 (lowest 160 meter frequency in MHz) = 558 feet. If using insulated wire, shorten the overall length by 4% (-22 feet). 558 feet minus 22 feet = 536 feet. The length of the feed line (450 ohm ladder line) may require some final adjustment as it may become part of the loop and serve as a radiator. My loop is 520 feet of insulated wire with a 28 foot lead in, and is resonant slightly below the bottom of the 160 meter band. I intend to shorten the insulated wire to exactly 508 feet the first time I take it down for any maintenance (Which may be a long time). You do not need to get it that close to resonance on the lowest band, but for us anal retentive types it is an interesting distraction.
Tuning. This design is a full wave (or longer) at the lowest frequency for which it is intended. It need not be cut to resonant length even for the lowest frequency band intended. It can be cut longer, even much longer, letting your tuner handle the mismatch. The most practical design however is to cut it to resonance at the lowest frequency of the lowest band targeted as outlined above. With some adjustment of the length of the feed line, you may find several bands or portions thereof which will be resonant enough to allow you to bypass the tuner. If using a separate balun to feed your tuner, try to keep the connecting coax as short as possible. 10 to 15 feet or less should not be a problem.
How High ? Ideally, this antenna should be hung as high as possible, but even at very low height (as low as 10 to 20 feet above the ground) it can be very effective. Be sure to hang it high enough that it cannot be contacted by anyone on the ground. It can be hung beneath the canopy of the trees as long as the wire does not touch any leaves, branches etc. Note: If insulated wire is used, contact with leaves or branches is permissible, but is best avoided to prevent the insulation from eventually being damaged.
What if I don't have room for a 160 meter loop ? Make the loop as large as your property will allow. If you can cut it for 160 meters go for it. If not, go for 80 meters or 40 meters. A 40 meter loop requires less than 130 linear feet of insulated wire. That is a square of only 33 feet per side. Nearly any suburban residential lot should be able to accommodate that size. Remember the sides need not all be equal, it can be almost any shape that encloses the largest area possible. EXPERIMENT !
At first blush, this design may appear to be just a big short circuit because each leg of the feed line is connected to the end of a big loop of wire. True, it is a short circuit at D.C. but at Radio Frequency which is A.C. it is an excellent radiator. Do not be misled by reports (mostly from those who have never tried it) that this is a vertical radiator or “cloud warmer” design. When used with ladder line you will be impressed with its performance as a transmitter antenna and surprised at how quiet it is as a receiving antenna. Naturally though, performance will increase somewhat with height above ground.
I strongly suggest the use of 12 gauge stranded, insulated, copper wire, which can be purchased at Home Depot and other home improvement centers for about $ 40 for a 520 foot roll. That is enough to make a 160 meter loop. The loop should be hung as high as is practical, and should be in the approximate shape of a big circle or square. It need not be perfectly horizontal, and the shape can really be a big square, or rectangle or any multi sided shape, so long as the two ends meet at convenient point where an insulator can be used to attach the feed line. The most critical element is that the loop should encircle the largest AREA possible. A circle, or square, or rectangle, is much better than an elongated oval, or triangle, or dog bone shape. My 160 meter loop is 7 sided, with none of the legs of equal length or height, and it is a stellar performer. It is 25 feet above ground at the highest point, and 15 feet at the lowest. Mine is 520 feet in total length.
The loop can be attached to poles, trees, buildings etc., whatever is convenient. It is best of course to try to avoid running it with a leg parallel to nearby power lines. NEVER INSTALL ANY PORTION OF THE LOOP OR FEEDER LINE ABOVE OR BELOW A POWER LINE! The loop can be free floating (that is attached so that it can be pulled tight at the two ends and just looped through the guy lines that hold it up) or it can be firmly attached at one or more points as necessary. I use heavy (5/16 in.) black Dacron rope with a knot that is loosely tied to the wire. Mine is free floating so that if I disconnect the center insulator, the entire loop will go slack, but will still be loosely attached to the guy ropes. This is probably the best way to hang it, especially if it is attached to trees, as it allows for some movement as the trees sway, and does not stress the wire. If it is left free floating or partially so, it is a good idea to leave a little slack in the wire. There is no reason to stretch the wire guitar string taut. Unless you are using a high power transmitter in a very wet environment, it is not really necessary to use insulators to attach the Dacron guy ropes to the wire when using insulated wire, as the Dacron rope does not tend to absorb much moisture. I highly recommend the use of Dacron rope due to its strength and resistance to deterioration from sunlight and the weather. This rope can be purchased from most ham radio stores and is available from MFJ, HRO, and AES. Note: This may be called Dacron, Dacron/polyester or Dacron/nylon rope, or just polyester antenna rope, and should not be confused with Dacron wire rope, which has wire woven into it, and is sometimes used as an antenna wire. It is unlikely that you will find Dacron rope at a local hardware or home improvement store. Whatever type insulator you choose as the attachment of the two ends of the wire to the lead in, be sure to solder the antenna to the lead in wires well. I use a piece of PVC pipe as the insulator. The antenna can be fed at ANY point. I chose to feed it near the end of one leg for convenience.
I want to stress the importance of several points:
Remember, each end of the wire loop attaches to one of the legs of the lead in wire.
The higher above ground you can hang your antenna the better.
Enclose the largest area possible. This is the key to great performance.
For best long term results, I recommend the use of #12 insulated stranded copper wire. The best color is black, as it is sunlight resistant and less visible. This wire is also quite strong and flexible, and the insulation reduces precipitation static.
Use black Dacron rope (Not Dacron wire rope), to tie it up. Just about any other rope will rot away in a year or so. NEVER use metal wire or wire rope as it will interact with the antenna and screw things up royally. If you choose not to use Dacron rope, I suggest using heavy, non - metallic Trot Line Cord which can be found at sporting goods stores or in catalogs catering to cat fishing enthusiasts. It is strong and rot resistant but will not last nearly as long as Dacron rope.
For best results, I recommend that you do not try to use it at a frequency lower than the lowest resonant frequency. (Don’t try to load an 80 meter loop on 160 meters) It will perform well at higher frequencies with a tuner. If you experiment with loading it on a lower than resonant frequency, try it at very low power while attempting to adjust your tuner for minimum SWR.
Do not feed It with coax. This is a MULTI band antenna, and 450 ohm ladder line will have very little loss at non resonant frequencies. Ladder line is not that difficult to deal with. You can cut a slit in your attic etc. to feed the line in. Just keep it 3 or 4 inches from any metal and don't bend it in a radius tighter than 10 or 12 inches. You can run it to a 4:1 Balun under your eaves for example, and then run a short length of coax into your shack. Experiment a bit and see what works best for you.
If you have trouble getting it to tune to minimum SWR on any band, try lengthening or shortening your ladder lead in line. Some bands may exhibit lowest SWR when the tuner is bypassed. Experiment as necessary.
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Good luck with your project. Chances are you will be so pleased with this antenna that you will no longer use any other wire antenna at or above the resonant range of your Horizontal Loop. Please let me know how it works for YOU.
If I can be of any assistance, please e-mail me at k5rcd@wildblue.net
73, K5RCD - Randy.
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