## The Relationship between Gain and Power Output in Signal Boosters

As you can see, around 12 dB (15 x) is the maximum gain that you need on a direct-connection booster. Direct-connection boosters with 20 dB or more gain are only wasting its power by generating signals that interfere on adjacent cell phone channels – actually causing less power where you need it. Remember that you only have 3 watts, which is now divided over a bigger bandwidth, causing harmful interference.

#### Why do we need higher gain boosters?

Let’s look at a 40 dB mobile wireless 3-watt booster. We need more gain because when the cell phone has to transmit to and receive from the booster’s inside antenna (which is about 1-2 feet from Have you wondered why a direct-connection **cell phone signal booster** with 12 dB gain has 3 watts of power output, and a wireless booster has 40 dB gain and 3 watts of power output? Gain is the number of times the power into the booster is increased at the output of it. Gain is expressed in dB’s, a way to make large numbers easier to write. For example, 10 dB is a gain of 10 times, 20 dB is a gain of 100 times. For example, 1 watt into a booster which has 10 dB gain puts out 10 watts. But that’s not the whole story.

#### What if the booster is only capable of 3 watts output?

The booster is then over-driven. Too much input power results in 3 watts of distortion, just like yelling into a microphone and distorting a hi-fi system. The same happens to the **cell phone signal booster**, which causes it to interfere with adjacent channels on the cell tower. The maximum power that can be applied to a 10 dB 3-watt amplifier is .3 watts, which gives 3 watts of undistorted output. A cell phone connected to a **direct- connection booster** with normal cell phone maximum power (.2 watts) going into the booster and a gain of about 12 dB gives 3 watts of undistorted output power to the cell tower. Any more input power would not increase the output, but only distort it, which causes harmful interference. the cell phone), the signal is much weaker into the booster than the .2 watts that was going directly into the direct- connection booster. The signal is now approximately 660 times weaker when it enters its input. It just so happens that a 40 dB gain booster will put out 3 watts with that input, so you can see different gains are needed for different applications. Also, in an automobile situation with the **outside antenna on the roof** of the car and the inside antenna near the headrest, 40 dB is generally the maximum gain before the booster starts causing interference.

With building applications, the cell phone is much farther from the inside antenna; therefore, a higher gain booster is needed. A 50 to 60 dB gain will generally give good coverage in most building applications. **Signal boosters with higher gain** require much greater antenna separation. For example, a 72 dB gain booster requires 4 times more antenna separation distance than a 60 dB booster.

10 dB = gain of 10

13 dB = gain of 20

16 dB = gain of 40

19 dB = gain of 80

20 dB = gain of 100

30 dB = gain of 1,000

40 dB = gain of 10,000

50 dB = gain of 100,000

60 dB = gain of 1,000,00