Understanding a little bit about TV antenna amplifiers

I was inspired to write this article after a discussion with a coworker. They said something like, “an amplifier can’t give you more range, it can only give you more signal.” That’s sort of true, but it also really typifies the kind of misunderstandings we have about amplifiers.

It seemed like a good opportunity to go really deep on the subject of amplifier and what they are capable of.

A basic understanding of amplifiers

An amplifier is any device which increases the quantity of something while retaining its quality. That’s a pretty broad definition. Until the late nineteenth century it was all you needed. Before that, if you thought of amplification, perhaps you thought of a device like the one you see above. That’s not really an amplifier, it’s a megaphone. A megaphone, at least the simple one you see there, doesn’t amplify sound. It seems like it does. What it does is direct it so it’s going in the same direction. Instead of sound waves getting scattered all about, it’s focused in one direction. More of it reaches your ears, which is why it seems louder. But this device didn’t “make” more sound because that’s impossible. At least it’s impossible without using electricity.

Modern amplification

This spiffy looking fellow is Lee de Forest. Although he had very little actual training or prior experience, he invented the world’s first working electronic amplifier in 1906. This was the first device that was able to increase the level of a signal by adding more electricity to it.

This may have been one of the most important inventions of all time, not because of what it was, but because of what it enabled. With amplifiers, radio signals could be transmitted over greater distances, making them useful. Sound could be amplified to fill a room. Even more important, small amounts of electricity could be controlled precisely, eventually leading to literally every electronic device ever and the whole internet. But that’s another story for another day.

The very basis of an amplifier was that it preserved the characteristics of a weak signal but converted it to a strong signal.

The vacuum tube

This device is a vacuum tube, so named because there is no air in it. By controlling the flow of electricity, it is capable of increasing signal levels. The lack of air isn’t really a necessity but it increases the reliability of the device.

Vacuum tubes were the only form of amplification until the 1960s, when transistors became readily available. The transistor does the same thing as a vacuum tube but does it in an enclosed package that is much smaller and much much more reliable. This technology forms the basis of all the amplifiers we use today, with few exceptions.

The relatively inexact amplification created by vacuum tubes imparts a “warm” sound to music when it’s amplified. For that reason, tubes are still used in high-end audio amplifiers and musical instrument amplifiers.

Amplifiers vs. digital signal processors

It’s only been in the last 20 or so years that cheap digital signal processors (DSPs) have been available. The DSP is sort of the “holy grail” of amplification. It’s a device that can, on a basic level, “understand” the signal it’s receiving and reconstruct parts of it that are missing.

An amplifier, even the best amplifier, can only give you more of what you already have. Here’s what I mean. Let’s say that I wanted to send you this image.

The problem is that by the time it gets to you, it’s much weaker, and the transmission hasn’t been perfect because something got in the way. So it looks like this.

With a traditional amplifier, you can only fix so much. You might get something like this:

And that might be enough for you to realize that it’s supposed to be the word “banana” but it’s not really clear and precise.

A digital signal processor can look at the signal in ways that you can’t. It can search for meaningful patterns that might help reconstruct the signal in such a way that it can be better interpreted. After some digital signal processing, you might have an image like this:

No one is going to mistake that for the original signal but it’s a lot easier to read the word “banana” there and that’s all that really matters.

Digital signal processors are used routinely in cell phone transmissions as well as over-the-air television broadcasts to make the most of weak signals once they are amplified. As you can see, they can make a huge difference.

Can an amplifier “add range?”

No, it cannot. A DSP can’t either. But, today’s advanced amplifiers can help a smaller antenna act like a bigger one because of the way they handle digital signals.

Digital signals are ones and zeroes sent across space. Practically every wireless transmission you encounter today is digital, from your cell phone to your Wi-Fi to over-the-air television. The only exceptions are things like radio and remote controls that use older technologies. With a digital signal, the actual level of the signal doesn’t matter, The only thing that matters is whether you can understand it.

Let’s say I’m sending you this picture, where everything is either solid black or solid white:

Now, you understand this signal and you’re not going to understand it any better if I make it really big like this:

You’re also not going to understand it any worse if I make it pretty small and blur it out:

In fact, even if I mess it up and make it really hard for you to perceive it…

I can still use a DSP and restore pretty much all of it back.

So the only thing that matters is if the amplifier and DSP, working together, can tell the difference between what’s supposed to be solid black and what’s supposed to be solid white.

Where noise comes in

An amplifier can work to restore a signal and be really effective, but the problem comes when you introduce noise. Noise comes from naturally occuring electrical variations in the air and in wires. If our signal is sufficiently weak and sufficiently noisy:

then our signal processor will have a hard time reconstructing it. It may end up looking more like this.

Eventually, with enough noise and a weak enough signal, we stop being able to see the pattern at all.

What today’s amplifiers can do

Today’s low-noise amplifiers and digital signal processors can do some amazing things. As long as the signal is clear enough and strong enough to interpret the difference between “on” and “off” you’ll get really great reception. That means you can often make do with less signal coming in. That’s why you can end up using a smaller antenna that simply receives less. However, eventually the signal is just lost in the noise and there’s nothing you can do. Using a larger antenna will help up to a point, but eventually the signal just “falls off.” That’s why you’ll hardly ever be able to get a TV signal reliably from more than about 75 miles.

Wrapping it all up

With a modern amplifier, you can use a smaller antenna to get signals from further away. Is that the definition of “adding range?” I suppose some folks could see it that way. I’d say that isn’t true, even if that is the net effect. By understanding the ways that amplifiers actually work, and the way that digital signals are read and understood, you’ll get a better sense of what’s possible.

And, of course, when you’re ready to get an amplifier for your antenna or for anything else, I hope you’ll shop at Solid Signal.

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.