Some common questions asked about wire antennas are as follows: What kind of wire should I use? What gauge is best? Can I use insulated wire? Can I use common household electrical wire? Should I use solid or stranded wire? Should the wire be made of copper, or can steel wire do the job? What’s all this talk about “skin effect?”. How long can a length of antenna wire be without having a support? Can I use wire to support a wire antenna, or must I use non-insulated antenna rope? Read on, and you’ll find some answers to these and other questions. Copper wire is generally best to use for antennas, although many tests have shown that the propagation difference between good conductors such as copper and aluminum
versus stainless or galvanized steel are minimal. The main advantage of using copper wire for an antenna is that it’s a better conductor than steel, and although it will oxidize, it won’t rust. Oxidation is copper’s version of rust. It’s a greenish or black covering that develops when copper is exposed to air. The black version of copper oxide is caused by heat. Chemically the “stuff” is called copper oxide.
The advantage of a copper oxide covering over an iron oxide (rust) one is that copper oxide may discolor the copper, but it won’t flake away and break apart like iron oxide does, thus the integrity of the wire will remain intact for a much longer period of time. For example, compare copper plumbing to iron or steel pipe. Now
you get the idea! Copper oxide does have some conductive properties, but not much.
You’ve probably heard about “skin effect”. That’s the property of radio frequency energy that allows it to flow on the outside of a conductor rather than within the entire conductor. The thicker the gauge of wire you use the broader the bandwidth of the antenna will be. However, it isn’t practical to use 1/2″ copper pipe for, let’s say, a 40 meter dipole (67 feet), although there are manufacturers that do use that thickness material in the manufacture of their beam antennas. Let’s confine our discussion to the construction of wire antennas, and leave the matter of beam antennas for another article.
I prefer to select the gauge of wire based upon physical considerations rather than electrical ones. In other words, how long is the antenna going to be, and what is the heaviest gauge wire that can be obtained for the project without breaking the bank. What is the longest length of unsupported antenna? Generally, most amateur radio operators prefer using a 14 or 12 gauge stranded copper wire for 80 or 40 meter dipole antennas. This type of wire is generally available in most ham radio stores and has minimal stretch properties. Others may use a “copperweld” design, which is simply a single copper coated steel strand, available in most common sizes from 6 to 20 gauge. The advantage of copperweld wire is that it won’t stretch, like common soft drawn house wire does. I don’t suggest you use common house wire for your antenna project, as your 15 meter antenna may become resonant on 20 meters after a good windstorm! Remember that “skin effect” will cause the RF energy to flow around the outer layer of the “copperweld”, which is the copper part, and not the steel portion of the strand. Thus the 40% conductivity rating of copperweld will not be much of a factor when using it for an antenna. Copperweld wire generally has a mind of its own, tangles easily, and can readily kink, which is why most amateurs use stranded copper wire. By the way, never install a wire antenna with a kink or sharp bend in the wire because it will most likely eventually break at that point.
You may use either rope or wire to support your antenna. If you decide to use wire, don’t cut the wire
supports at or near the resonant point of your antenna. If you do, break up the wire support with additional insulators, so as to avoid having a resonant length of wire near your antenna.
The short answer to the question as to whether or not you can use insulated wire for an antenna is “Yes you can”. Insulated wire will make your antenna appear physically shorter at the resonant point, but the difference is slight (estimated to be about 2%). The advantage of insulated wire is that the copper inside the insulation will be protected from oxidation, and may actually add some physical strength to the strand(s) of copper. It doesn’t make much difference if the wire is solid or stranded, but stay away from soft drawn copper wire because it will stretch, insulation or not!
Last but not least, remember your basic safety rules. NEVER install your antenna above, below or near electric utility wires or attach the end of your antenna wire to a utility pole.
