How can an antenna be made of plastic and still work?

TOPICS:

Most folks I know think antennas are ugly. In fact, they think the ugliest antennas are the ones that look like big collections of metal sticks. They look at something like this:

and their answer will tend to be “not just no, heck no.” And yet, antenna enthusiasts will tell you than an antenna like this, our Xtreme Signal HD8200XL, is going to outperform practically any other TV antenna you’re likely to get. There are plenty of areas of the country where it’s this antenna or nothing, at least if you want to get decent reception.

That’s why I think you could be forgiven for being skeptical of an antenna like the Televes Dinova Boss Mix. After all, it doesn’t look like any other antenna you’ve ever seen before. It doesn’t look like an antenna. It looks more like some sort of 1970s spaceship. And, it’s made of plastic. Everyone knows plastic can’t be used for an antenna, right? Sure it has some metal bits that stick out, but those couldn’t possibly be the only parts of the antenna that do the work? Or could they be?

Here’s the real secret to how this all works.

The secret is simple. Inside that plastic shell (which we call a “radome”) is the actual antenna itself. It’s a lot smaller and thinner than you would expect, because it’s supported by all the plastic bits inside the antenna. Antennas themselves don’t work particularly differently whether they are made of thin bits of metal or thick ones. So, encasing the antenna in plastic has the ability to actually make an antenna smaller because it doesn’t need to be thick enough to stand up by itself.

Inside the Dinova, there is the antenna, which is actually a circuit board, as well as the amplifier that helps provide a stronger signal without introducing a lot of noise. There’s also a combiner that allows the signal from the internal antenna to mix with those pull-out metal bits on the sides. Finally the whole thing goes into a balun. A balun converts the 300-ohm resistance of the lines inside the antenna into a 75-ohm resistance so it can travel efficiently over coaxial cable. Coaxial cable has better shielding than 300-ohm cable. More importantly it’s been popular for generations thanks to its use in cable television and satellite television applications.

Doesn’t the plastic block the signal?

Everything that a radio signal passes through will “attenuate” it (that is, lower the signal level) by a little bit. However the plastic on these antennas is designed to let as much signal through as possible and so the amount of signal lost isn’t a concern. We tend to say that the signal passes through the radome, as if no signal is lost, because so little signal is actually lost there.

Bottom line: is a plastic-covered antenna better or worse?

The real determination of an antenna’s effectiveness isn’t whether or not it’s covered in plastic. It’s how the elements are sized in comparison to the size of the radio wave being received. In a perfect world, you would want an antenna to be the exact size of the radio wave being received. However, TV signals have fairly long waves — sometimes over 6 feet long. AM radio signals have even longer waves. Luckily, it turns out that you do pretty well if you use an even fraction of the size of the wave, such as 1/2, 1/4, 1/8, etc.

Larger antennas like the HD8200XL will use half-wave dipoles or quarter-wave dipoles, so that the antenna’s receiving element is exactly one-half or one-quarter of the size of the wave. Smaller antennas like the Dinova will use eighth-wave dipoles so that the element is one-eighth the size of a wave. The smaller the fraction, the less effective the antenna is going to be. You can compensate somewhat with amplifiers, that’s true. However, plain and simple, a larger antenna is going to give better reception. At that point you only have two questions. Do you actually need better reception? Remember digital signals don’t work differently whether they’re strong or weak as long as they’re received. The other question is, of course, if you can even put a gigantic antenna on your roof.

No matter what you need for an antenna, you’ll find it when you shop at Solid Signal. Have more questions? Call us at 888-233-7563 or fill out the form below.

About the Author

Stuart Sweet
Stuart Sweet is the editor-in-chief of The Solid Signal Blog and a "master plumber" at Signal Group, LLC. He is the author of over 10,000 articles and longform tutorials including many posted here. Reach him by clicking on "Contact the Editor" at the bottom of this page.