What is “noise floor?”

Get to know the right words and you can describe anything. We talk about “noise floor” with any sort of RF signals, because it’s an important concept. Noise, you see, is everywhere. The world is full of stray electronic signals that are the enemy of good reception whether it is on cable, on satellite, or through a TV antenna. Some of it is as old as the universe itself and some is generated by the devices around us.

What is RF noise?

We use the term “noise” to refer to any RF radiation that we humans didn’t make intentionally. It includes the naturally occurring radio waves that the universe has always had, plus unintentional emissions from all that electrical stuff we’ve created.

It’s impossible to eliminate all the noise around us. We can use special rooms to make it as low as possible, but in the real world it’s just … there. So any antenna or receiver has to account for it. We need to design signals that are stronger than that noise, or else there’s no point to any of it.

Signal always must be stronger than noise

When we’re trying to receive a signal of any kind, it has to be stronger than the noise around it or else it won’t be heard. Think about whispering in a quiet room. There’s no noise, so the whisper is easy to hear if you’re close. Then think about a dance club where there’s sound everywhere. No matter how close you get, you’ll never hear that whisper because there’s too much noise. This is exactly the same situation we see with RF signals.

Here’s where noise floor comes in.

So we need a term that sort of means “that background noise that you have to overcome or else your signal is lost.” And there is such a term — noise floor. Noise floor is the total amount of noise surrounding a signal. If the signal is weaker (lower) than the noise floor, it’s gone. If it’s above the noise floor, there’s a chance of receiving it.

The idea of “noise floor” is closely tied to the term “noise figure” which describes how much noise is added to a transmission just through the use of amplifiers, long cables, etc. If the noise figure for an amplifier is 1dB, then that also says that the noise floor goes up by 1dB after the signal is amplfied. It’s just another way of saying the same thing.

Noise just won’t go away

All of this is important because you really can’t get rid of noise. I mean you can if you take the signal and reprocess it and create a new signal, but that’s a pretty heavy-duty process which isn’t going to happen in a simple amplifier or splitter. There’s no such thing as a “noise filter” really, anything that claims to filter noise passively is just taking frequencies that “probably” aren’t used and isolating them. The amount of noise that actually affects the signal is still there.

So, the bottom line here is that you should keep your noise floor low if you can, because once you have noise, it’s awfully hard to get rid of.

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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.