How Cell Signal Boosters Work

Signal boosters, also known as Bi-directional amplifiers or BDA's, work by capturing a signal outside the home, building, car, boat, warehouse, etc…, bring it inside, amplify it , and redistribute it.  For most of the products on this site, there are four main components: the Outside Antenna, the Amplifier ( booster ),  the Inside Antenna, and the cabling to connect everything. 

The Outside Antenna

The outside antenna can be omni-directional (can capture signal from all directions) or directional (works best when pointed directly at a cell tower). The benefit to omni-directional antennas is that they are easy to install and pick up signals in a 360 degree horizontal plane.  You want to mount them as high as possible where the signal is strongest.  A couple disadvantages of omni-directional antennas: 1) their gain is typically much lower than a directional antenna. 2) they are more prone to other RF interference.  The Cellphone-Mate CM100-S is a good example of a popular omni-directional outdoor antenna. The benefit to directional antennas (Yagi antennas) is that they typically provide more signal gain (power) than omni-directional antennas.  They are also less prone to other RF interference.  Because they are directional, they must be pointed toward a cell tower.  However, because they are directional and provide more gain, the tower can be much further away than is acceptable for an omni-directional antenna.  The Wilson 304411 Wide Band Yagi is a good example of a popular directional outdoor antenna.

General Purchasing Recommendation

Reasons to choose a Yagi Antenna:

Reasons to choose an omni-directional antenna: 

• If you are looking for the quickest and easiest installation possible
• If you have multiple carriers to provide coverage for and towers are not located in same general direction
• If you have at least 3 bars outdoor signal strength
• If you plan on using less than 50' of coax from the omni-directional antenna to the amplifier
• When given a choice among 3, 5, and 9 dB Omni-Antennas, Choose 3 dB for mountainous or urban areas, 5 dB for suburban or moderate terrain areas, and 9 dB only for flat terrain areas
• If you are sure you will be able to adhere to the antenna separation requirements for the amplifier you choose
  

The Amplifier 

Every amplifier (or booster) must provide at least two ports, an input and an output.  While higher end models will have more sophisticated circuitry, higher gains, and adjustable uplink and downlink gains, they all function pretty much the same.  The signal coming in from the outside antenna is amplified and sent to the inside antenna.  Every signal amplifier has a specification called Gain.  Without getting too technical, gain is defined as the ratio of output to input.  When specifying electrical power, gain is measured in dB (decibels).  dB numbers are derived from a fairly simple logarithmic function, however all you need to know is that every increase in 3 dB doubles the power.  Ex. 1 watt into a 3 dB amplifier would come out as 2 watts. 1 watt into a 6 dB amplifier would come out as 4 watts.   For more, please reference the following:

• 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 1,000,000

When searching for an amplifier for your particular application, please reference the following table:

Please keep in mind that this table represents general rules of thumb and the recommended applications and antenna separation distances may vary by product/manufacturer, outdoor signal strength, cable lengths and antennas.  Antenna separation distances are to keep your amplifier from going to oscillation.  In the audio world, this is analogous to getting a microphone too close to a speaker, thus producing feedback. If you choose directional indoor (wall mount panel) and outdoor (yagi) antennas or there is metal or multiple walls separating the antennas, often times these distances can be much shorter than the distances listed above.  Also, increasing the vertical component of the separation as much as possible will reduce the required separation as well.  These are straight line distances with both horizontal and vertical components, not distances based on the cable lengths. 

The Inside Antenna

Inside antennas, just like outside antennas, come in different shapes and sizes and serve different purposes.  All of the Wi-Ex products on this site have a small omni-directional antenna attached to the amplifier itself.  While this makes installation fairly simple, the unit must become part of your home décor as it must be installed in a central location and will be visible.  Most of the other in-building amplifier products on this site will have a separately mounted internal antenna.  The most popular antenna for providing omni-directional internal coverage is the ceiling-mounted dome antenna, such as the Cellphone-Mate, Inc. CM222.  This type of antenna is a little more difficult to install, but is less obtrusive.  Inside antennas can be directional as well.  If you are you looking to provide directional coverage for a large, open space or hallway, the Cellphone-Mate, Inc. CM248 wall-mounted panel antenna provides this.  A panel antenna can also be installed in an attic (facing downward) if you have tall ceilings.

General Purchasing Recommendation

Reasons to choose a ceiling mounted dome antenna:

• If you have access to an attic or crawl space where you can run cabling easily to the antenna
• If the coverage area is more or less sqaure, as opposed to rectangular

Reasons to choose a wall mounted panel antenna: 

• If the coverage area is large and more rectanguar than square
• If you do not have access to an attic or crawl space
• If you have access to an attic or crawl space and have very tall ceilings (mount in attic, facing downward)
• Are able to install it in a direction facing away from the outdoor antenna
• Are purchasing as a second antenna for a multi-floor system (installed on lower floor facing away from outdoor antenna)

The Cabling

The cabling and connectors used to connect the outside antenna to the amplifier as well as the inside antenna to the amplifier play a crucial role in how your system will perform.  Depending on the product, different types of cabling and connectors can be used.  Ex. Some of the Wi-Ex and Wilson products use standard RG6 or RG59 75 Ohm coax between the outside antenna and the amplifier.  This is the same coax used for your cable TV or satellite system.  While this type of cabling is less expensive, there are some drawbacks.  For cellular and PCS frequencies, on average, RG6 will lose 6-10 dB of signal per 100ft.  This is typically more loss than the outside antenna provides in gain.  Remember, you want your amplifier to receive the highest quality signal possible.  For this reason, it is recommended that runs using RG6 should be no more than 50 or 75 ft.  For most of the other products on this site, LMR-400 50 Ohm Coax is the standard.  In comparison, while LMR-400 is more expensive and thicker, it only loses about 3-6 dB per 100 ft for cellular and PCS frequencies respectively.  Based on this, LMR-400 can be run further than RG6 before there is a decrease in system performance.  For all three-piece systems (outside antenna, amplifier, inside antenna) it is recommended the amplifier be installed as close to the external antenna as possible.  Ex. If the external antenna is installed on a roof, it is recommended the amplifier be installed in the attic as opposed to the basement.  The shorter the cable length between the external antenna and the amplifier, the better.  Remember that there is no separation limit between the antennas and the amplifier, only between the antennas.

General Purchasing Recommendation

• Keep the cable lengths to a minimum.  Purchase only the lengths you need and do not coil or fold extra cable.
• Keep the cable from the outdoor antenna to the amplifier as short as possible (remembering that the amplifier should be installed in a location that has 110 AC power)
• Keep the cable length from the amplifier to the indoor antenna(s) as short as possible (while trying to adhere to the antenna separation requirements listed above - adjustable gain amplifiers and directional antennas may decrease the required antenna separation distance)

  If you have any questions regarding the information on this page or would like us to recommend a system for your specific application please feel free to Contact Us or fill out our Design Form.