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Mobile Broadband FAQ #18: What Does "Gain" Mean in Amplifier/Repeater Specs?

The mobile broadband experts at 3Gstore/EVDOinfo answer countless questions from our customers and from the EVDO Forums community every day - from general mobile broadband questions ("what the heck does 3G mean?") to specific questions about products to more advanced inquiries about what one can do with their mobile broadband service. The "mobile broadband FAQ" series addresses these questions in depth one FAQ at a time. To view ALL of the FAQs we've addressed in this series, visit EVDOinfo.com/faq.

The popular 62db gain Cellphone-Mate repeater kit

Wireless Signal Amplifiers, AKA "Repeaters," can be a great solution for many cell phone and mobile broadband users who are experiencing signal strength issues, but they are also the cause of more confusion than any other product we sell. A repeater is simply a wireless amplifier system that does not require a direct connection to cellular devices such as phones and modems. A basic repeater setup includes an amplifier and two antennas: one antenna (preferably mounted outdoors) draws the signal in and connects to the amplifier, which boosts the signal; the second antenna, connected to the other side of the amplifier, then rebroadcasts the boosted signal. Multiple cellular devices can then benefit from the boosted signal at once.

There are a wide variety of different repeaters available to fit the needs of different applications, and the options are often overwhelming to customers. One of the most confusing considerations when looking at the specifications for different amplifiers is the gain rating. If you look at the specs for any wireless amplifier/repeater, you'll see a listing for gain, which is measured in decibels (abbreviated as dB). For example, the repeater kit pictured at the top of this article features a 62dB gain amplifier.

People typically assume that "gain" means how much improvement they'll see from the repeater, assuming that if the specs say "40 db gain", then their RSSI will improve by 40 db, or that a repeater with a 60 db gain will result in twice as much RSSI improvement as a 30db repeater. This is not correct! With regard to wireless amplifiers, gain is the ratio of an amplifier's output power relative to its input power.

In simplified terms, the "gain" on a wireless amplifier's specs relates to how much coverage it can provide. The more gain the amplifier has, the larger the area to which it can boost signal: for example, a 62db wireless amplifier will be able to provide boosted signal to a larger area than a 55db wireless amplifier. That doesn't mean the 62db system is going to result in more improvement on your cell phone, but it does mean that you won't have to be as close to the rebroadcasting antenna to benefit from the signal boost.

For every 6db increase in gain, the coverage area doubles - so the Wilson SignalBoost DB Pro, which has 62db gain, can provide boosted signal to an area more than TWICE as large as what the Wilson SignalBoost DT, which has 55db gain. The actual area that an amplifier can boost depends on the many factors, though - there is no guarantee about how much coverage you are going to get from any particular wireless amplifier, no matter how high the gain is. Walls, layout of the building, interference, and signal strength (the weaker the starting signal, the smaller the boosted area will be) all play a role in how much coverage you'll see from a repeater.



If you are wondering how much improvement your phone/modem will see from a particular repeater, the "gain" is not what you want to look at. It is not possible to guarantee a particular number of decibels or bars of improvement you're going to see - there are too many factors to predict. The basic factors that will affect how much improvement you'll see from an wireless amp include: the strength/weakness of the original un-amplified signal, the antenna used (since signal is better outside, a repeater setup using a tall exterior antenna is likely to perform better than one used with a booster antenna; a directional antenna is also typically better as long as you know where the tower is), and the output power (for instance, a 400mw travel amplifier will not perform as well as a 3-Watt amplifier).


Related Links: 

• Read all FAQs
• Will an Antenna or Amplifier Help Me?
• View wireless repeater kits