Why is noise figure important to an amplifier?

One of the key features you should be looking for in a high-quality amplifier is noise figure. We’ve mentioned the term before, and while I could get highly technical, noise figure for all intents and purposes is the amount of noise, measured in dB, that an amplifier adds when it amplifies the signal. It’s impossible to add no noise at all, because even the best, most comples amplifier is going to amplify what it hears and then process out the noise as best as possible. A low noise amplifier is generally considered to have a noise figure of about 2dB or less.

Noise figure is especially important with digital signals. With a digital signal, it’s either there or it isn’t, but you need to realize that we live in an analog world. There’s no such thing as something purely digital, and when we say something is “there or it isn’t” what we really mean is that “it’s there, to the extent that the computer chips can pick it out of the noise surrounding it, or it isn’t.” That’s an important distinction. A strong signal has to be strong enough to make up for the noise surrounding it or the tuner won’t be able to pick it up. If you add noise to a sketchy signal, you make it harder to tune even if you make the signal stronger. That may not make a lot of sense at first. If your signal is so weak that it’s overwhelmed by noise… and that’s what happens in certain “fringe areas,” adding an amplifier, especially one with a high noise figure, can actually make matters worse.

That’s why we are careful when we make antenna recommendations. It’s very hard to tell whether or not an amplifier will help you. In order to get a benefit from an amplifier, you need a signal that’s weak enough that you have trouble tuning it but strong enough that it can overcome the noise figure of whatever amplifier you attach. That’s a pretty slim margin and without expensive test equipment it’s hard for an average person to know if they’re right where they want to be.