Why are outdoor antennas made of aluminum? Why does it matter that the Superbat has “real silver elements?” Does it really matter? You may be asking yourself these same questions, so let’s talk about good materials for antennas.
The purpose of one antenna is to conduct electricity, because radio waves are a form of electricity. So, One factor that must be possessed by an antenna is conductivity. Conductivity is a measure of how well any material conducts electricity. Materials that do a really bad job of conducting electricity, like rubber, are called insulators. Insulators are needed because otherwise we couldn’t touch anything electric. (It turns out that our skin makes a pretty good conductor; anyone who’s gotten a shock knows that.)
Part 1: A conductive material
It’s probably pretty obvious that most metals are good conductors, because any time you see some sort of wire it’s always made of metal. Connections between parts in a computer are gold, and all wires are made of copper. Not every metal conducts electricity equally. Let’s take a look at some common metals in order of their ability to conduct electricity. The top item on the list is the most conductive.
1. Silver
2. Copper
3. Annealed copper
4. Gold
5. Aluminum
6. Calcium
7. Tungsten
8. Zinc
9. Nickel
10. Iron
Silver is the most conductive, meaning that it’s going to do the best job pulling electricity out of the air. Copper, that favorite of wire makers everywhere, which is close to the top of the list. Iron used in cheap indoor antennas, it is near the bottom of this list but still does a passable job.
Part 2: A material that resists oxidation
Silver is the ideal material for an antenna because its silver elements are encased in plastic. However, an antenna made of silver would be a disaster, because oxidation occurs when the metal in the open air. Silver turns into silver oxide ,Iron turns into iron oxide, which we call rust. Copper turns into copper oxide, which is that green stuff on the outside of the Statue of Liberty. Most metals are prone to oxidation in some form or another. Oxidation affects the conductivity of metal, so a material that oxidizes easily is a bad choice for an antenna if it’s in open air. Some oxides are fairly stable, like aluminum oxide; it forms a thin dull layer over aluminum that doesn’t really hurt conductivity very much. Plain iron, as we all know, oxidizes poorly. An untreated iron will rust out quickly. Steel, which mixed iron with carbon, doesn't oxidize as easily. Gold hardly oxidizes at all.
Considering only oxidation, the best material for an antenna would be gold or stainless steel. Of course, this leads us to part 3…
Part 3: Cost and structural integrity
The structural integrity isn’t important for an indoor antenna… you hope a 50mph wind doesn’t ever blow through the house. The plastic surrounding the Superbat antenna is good enough. For outside, you need something that won’t bend too much in the wind, and ideally you want something light enough that if it does fall, it won’t tear a hole in your roof.
Gold may be a decent conductor and great at resisting oxidation, but it’s way too expensive to build an antenna with. It is also fairly soft and would bend over in a stiff breeze. Brass and Copper are also fairly soft and oxidize easily. Iron is cheap and holds up well, but it’s heavy and it’s a poor conductor.
Looking at outdoor antennas, it’s easy to see why the combination of light weight, strength, conductivity and the way it oxidizes make it perfect. Indoor, the best choice is silver, as long as you can keep it out of the air and use something to hold it up. This was not possible in the past, which is why older antennas were made of iron or brass. Now, the Superbat can combine the structural integrity and low cost of plastic with the conductive power of silver to outperform other indoor antennas.