LOOP SKYWIRE ANTENNA
The Loop Skywire Antenna, is a very effective design for DX. This omni-directional, multi-band antenna performs well from the lowest frequency band for which it is designed, all the way through 6 meters if your tuner and balun will handle that band. It must be understood that an antenna tuner will be necessary to use this antenna. I recommend 450 ohm ladder line as the feed line. You will need a 4:1 balun transformer either in, or near your tuner.
To determine the resonant length of the wire, we use the formula: Length (in feet) = 1005 divided by frequency (in MHz), multiplied by the velocity factor of the wire used. For example, a 160 meter loop is 1005 divided by 1.800 (lowest 160 meter frequency in MHz) = 558 feet. Multiplied by .975 (for 12 and 14 AWG stranded, insulated electrical wire) = 544 feet. The length of the feed line (450 ohm ladder line) is insignificant. This design is a full wave at the lowest frequency for which it is intended.
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.
This design may appear to be 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 low angle radiator. Do not be misled by ignorant reports (especially from those who have never tried it) that this is only a vertical radiator or a “cloud warmer.” When used with ladder line, as these plans direct, you will be impressed with its performance as a DX antenna and surprised at how well it receives and with very little man-made noise.
I suggest using 12 gauge stranded, insulated, copper wire, which can be purchased at Home Depot and other home improvement centers. If you are building the 160 meter loop, have them measure and cut your wire to length so you don't have to buy a 1000 foot roll. 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. 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.
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 should be free floating (That is attached so that it can be pulled tight at the insulators where the wire passes freely through.) There is no reason to stretch the wire guitar string taut. I highly recommend the use of Kevlar or Dacron rope due to its strength and resistance to deterioration from sunlight and the weather. This rope can be purchased from most ham radio and hardware stores. The antenna can be fed at ANY point. It DOES NOT have to be fed at a corner, as some folk would have you believe. The feed line should hang away from the antenna wire at as close to a 90 degree angle as possible to prevent coupling of the feed line to the antenna wire.
KEY POINTS TO FOLLOW FOR BEST PERFORMANCE, RELIABILITY AND LOW MAINTENANCE:
Enclose the largest area possible.
For best long term results use #12 insulated, stranded copper wire. The best color is WHITE, as it is sunlight resistant and less visible. This wire is also quite strong and flexible, and the insulation reduces precipitation static.
Use Kevlar or Dacron rope (Not Dacron wire rope), to support the antenna. Other rope will eventually rot and fail.
For optimum performance, do not try to use the antenna at a frequency lower than the lowest frequency you cut it for. This antenna is designed as a full wavelength at its lowest frequency, and multiples of a full wavelength at higher frequencies.
Do not feed it with coax! Again, for those of you who "heard it from someone blah blah blah..." DO NOT FEED THIS ANTENNA WITH COAX!! This is, was, and always has been designed as a MULTI band antenna, fed with open ladder feed line. Coaxial cables were not even invented back when this antenna was designed. If someone tells you to feed it with coax, they just plain do not understand balanced and unbalanced feed lines!
These big antennas are a large target for a lightning strike, either a direct or nearby hit. They can also build up a significant static charge from atmospheric conditions. You should ground the feed line when the antenna is not in use. The old style twin bladed knife switches work perfectly for this application. One side to ground, the other to your transmitter.
Enjoy the antenna, and good DX