How is antenna performance measured?

TV reception is a funny thing. While we do our best with the wide variety of tools we have, there’s no way to guarantee that a particular antenna will work in a particular location, short of actually putting it up there. However, we do have a lot of tools that help us predict what an antenna will do and feel pretty confident about it. One of those tools is the antenna’s measured performance.

Antenna performance can be measured several different ways, depending on how precise you feel you need to be. Let’s take a look at how we measure an antenna’s performance and look at how it’s possible to make a pretty good guess about how an antenna will do in your home.

How performance is measured

We say that an antenna has a “gain” number and that’s the number that we use as a general guide. Sometimes we’ll split that number out into VHF and UHF, since different parts of an antenna are used for different frequencies. Gain is measured in decibels, or dB. Decibels are a relative measurement that help you understand how much more of something you have. When you see an antenna has a 14dB gain, there are three possibilities:

  • The lab can measure gain against something called a “reference dipole” which is a very basic antenna that everyone agrees to use for measuring stuff. When a reference dipole is used, generally gain numbers are quoted as “dBd.”
  • The lab can measure gain against a theoretical antenna called an “isotropic radiator.” This means it’s not a real-world test but the number is better at predicting what you’ll get in an ideal condition. When this is the case, gain numbers are quoted as “dBi.”
  • If the lab uses another method, they will quote gain numbers as “dB.” This method compares the antenna to whatever the lab used to test. Often times they will use a bare copper wire. They may also leave the signal meter disconnected. This provides a basic measurement.

Getting more detailed

While we’ll often say an antenna has a gain like “15dB in the UHF band” that’s still pretty broad. In order to see how an antenna performs over the entire frequency range you need to look at a plot. In a typical antenna plot you’ll see that the performance of an antenna changes depending on the frequency that it’s trying to pick up. Two antennas both rated with the same overall gain number might perform differently because of the actual channels you’re trying to pick up, and that’s important because the channel allocations are different in every city.

Getting even more technical

If you really want to understand an antenna’s performance, you need to realize that most antennas are directional. That is, they perform differently depending on how you aim them. So if you’re really going to delve into antenna performance, you need to look at a set of charts  like this one:

polarplots

These charts were generated by Televes’ testing facility in Spain, which is one of the most complete and detailed facilities on the planet for antenna testing. The terms “P.E.” and “P.H” refer to fairly complex physics formulas. In general I’ll look at the smaller of the two just to be safe.

You can see that these antennas operate fairly directionally. The “LR” versions focus a lot more gain at zero degrees (the front) so you can get better reception in a narrower area.

The right side shows amplified and unamplified gain charts which show performance over frequency. Here you can see that the Televes antennas don’t perform well at all over 700MHz, which shouldn’t bother you a bit. US television frequencies stop at 600MHz.

What you should learn here

Here’s what to interpret from looking at a gain chart and polar plots. You’ll get an idea how that particular antenna is going to perform. At least you’ll see how it performed in one testing location. When you get the antenna into place, things may be different. Tons of factors can affect antenna performance. From the trees and hills in front of you to the weather on a particular day, it all affects antennas. Of course, starting with the best information will help. In the end the only true measure of how an antenna will perform for you… is how it does perform.

If you’re looking for any sort of information on any antenna we offer at Solid Signal, call us at 888-233-7563. Real antenna technicians are waiting to take your call during Easy Coast business hours!

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 8,000 articles and longform tutorials including many posted here. Reach him by clicking on "Contact the Editor" at the bottom of this page.