If you look at a modern yagi antenna like our Televes DAT790 Mix, something odd will begin to occur to you. If you really begin to look closely, you’ll see the cable is connected to a small chunk of metal in the middle, which is isolated from everything else by a lot of plastic. Almost all of the antenna that you see isn’t even connected to the cable at all. Does that mean this antenna is a fake, or a phony, or that we’re putting something over on you?
It absolutely does not mean any of those things.
It all comes down to what a “yagi” antenna really does. The whole point of a yagi antenna is to focus all of the signal that’s coming in onto a single, relatively small point. The part of the antenna that’s connected to the cable is called the “receiving element.” It’s the part of the antenna that, like its name implies, actually does the receiving. The rest of the antenna, the part you can actually see from a distance, is designed to focus all the signal on the receiving element.
The parts in the front are called “directors.” They gather signal from a large area and focus it on the front part of the receiving elements. The large parts in the back are called “reflectors” and they take even more signal and focus it on the back of the receiving element so that even more signal — close to twice as much — is available.
You might be asking yourself how these metal posts and largely empty spaces can focus anything. After all, you’re probably imagining that this could all work the way I describe it, if all these things were made of glass and if they looked like lenses and mirrors. The trick is, they actually are mirrors and lenses, only they work for TV signals.
TV signals are electromagnetic radiation, just like light, but at a much lower frequencies. Low frequencies mean that the waves are a lot longer… a light wave is a few millionths of an inch wide while a VHF antenna wave is several feet wide. When you’re talking about such large waves, it’s a lot easier to focus them. Think of how air and water can go through a screen door because they are made of tiny particles but bugs, who are much larger than air particles, cannot. The screen door has “reflected” the bug even though it isn’t solid.
This is actually kind of the point of a yagi antenna, that simple bits of it can be used to focus signal on what is actually a very small area. Most large antennas work this way because a yagi antenna is nearly as efficient as an antenna which actually uses multiple large, wired elements. (We call that sort of antenna a log periodic.) Yet, the yagi is simpler to make and requires less delicate wiring, making it more durable.