Partly physics, partly fear. That’s a pretty good explanation of one of the most basic rules of cell booster placement. You should always have 15 feet between the base unit and the outdoor antenna, or for units without an outdoor antenna, between the base unit and the indoor antenna. Any less, and your device won’t work as well, possibly won’t work at all.
In order to understand why, you need a basic understanding of what a cell booster does. Don’t worry, I won’t get too technical. A cell booster is a perfect example of a repeater. Think of a guy who stands in the middle between two people who can’t hear each other. As one person talks, he repeats what’s being said to the other person. That’s all a cell booster does, really, although it also does some fancy amplification so that everything works even better.
So, you have the cell booster talking to your phone wirelessly, and talking to the cell site wirelessly, that’s a lot of communication. The booster is always trying to send the strongest possible signal everywhere it can, but there’s some concern there — if the signal from the booster to the phone is so strong that it can be picked up by the cell tower, really bad things can happen.
How bad? REALLY BAD.
Like, imagine a noise loop getting started that amplifies and amplifies until the cell tower turns itself off in order to avoid damage. Before that happens, imagine every cell phone in the vicinity going haywire because of that noise. That doesn’t sound like anyone’s idea of fun, in fact it sounds like a bad sci-fi/horror film.
Obviously no one wants that, so by law cell boosters are required to monitor themselves to make sure they don’t shut the whole cell network down. If they detect even the slightest hint of a feedback loop, they cut the power from the booster to the phone. This means they are less effective. So basically you are not getting what you paid for if you don’t make sure there’s enough separation between the two components. In a perfect situation, the outside antenna would be up at least 15 feet.
What happens if the two antennas are more than 15 feet away? Basically nothing. I mean, eventually you run into a situation where you lose some strength over the cable but that’s not going to happen in a house. If you’re in an industrial situation, you’d probably use multiple boosters and the cable runs would still not be long enough to make a difference.
So, bottom line, do yourself a favor and make sure there is 15 feet between the two pieces. Everything just works better that way.