How Cell Phone Signal Boosters Work

How Cell Phone Signal Boosters Work

Signal boosters, also known as Bi-directional amplifiers (BDA's), repeaters, or amplifiers, work by capturing a signal outside the home, building, automobile, boat, warehouse, etc…,with an exterior antenna, bring it inside, amplify it, and rebroadcast 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 in the direction of 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, making them suitable to picking up signals from cell towers in different directions.  You want to mount them as high as possible where the signal is strongest.  A few 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. 3) They are more prone to pick up the signal from the indoor antenna, resulting in system oscillation (see more on this below).  4) Most omni-directional antennas are not wide band meaning that they will not work well for any frequencies outside of the 850 MHz or 1900 MHz bands. The SureCall SC-100-S is a good example of a popular dual-band (850/1900 MHz) omni-directional outdoor antenna. The SureCall SC-288W is the only wide band (698-2700 MHz) omni-directional outdoor antenna we carry and is best suited for mountainous or urban areas.

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.  A disadvantage to the yagi antenna is that it will take more time to install because it must be pointed at your carrier's cell tower.  Also, if looking to boost the signal for multiple carriers and the towers are not in the same general direction this may not be the antenna for you or you will need to combine multiple yagi antennas on the roof.  The Cellular Solutions 504411 Wide Band Yagi is a good example of a popular wide band (698-2700 MHz) directional outdoor antenna which provides 8-10dB of gain and will work with all carriers and cell phone technologies in existance today.  Yagi's can also be band specific.  Band specific yagi antennas provide even more gain than a wide band yagi but must be pointed exactly at your carrier's tower as the beamwidth (pickup pattern) is much narrower than a wide band yagi.  An example of a popular band specific yagi antenna is the Wilson 301111 800 MHz Hi Gain Yagi Antenna.

Reasons to choose a Yagi (directional) Antenna:

  • If you are only interested in boosting a single carrer or multiple carrers with towers in the same general direction
  • If you have only 1-2 bars outdoor signal strength. Still recommended for higher signal strengths as well
  • If you Live on a relativly flat terrain.  Hills and valleys are acceptable, but generally not recommended for mountainous or urban areas.
  • If you need to use 50 or more feet of coax from the yagi to the amplifier.  Still recommended for lesser cable lengths as well.

We Recommend the Wide Band Yagi to the vast majority of our customers.

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 (typically 40+ feet of separation is required for most amplifiers)

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 RF 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:

dB Gain

Applicable To

Antenna Separation

<20 dB

Automobile, Boat

4 ft. or direct connect.

30 dB

Automobile, Boat

5 ft. or direct connect.

40 - 45 dB

Large Auto, RV, Large Boat

6 ft. – 20 ft.

50 dB

1-2 Rooms in a Home

30 ft. – 50 ft.

55 dB

Small home up to 1,500 sq. ft.

50+ ft.

62 dB

Up to 5,000 sq. ft. Home, Office, Warehouse

60+ ft.

68 dB

Up to 7,000 sq. ft. Home, Office, Warehouse

75+ ft.

70 - 80 dB

Large Home / Commercial Application

100 + ft.

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.  Some of our zBoost products 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 Cellular Solutions 501123 Ceiling Mount Dome Antenna.  This type of antenna is a little more difficult to install than one that is directly attached to the amplifier, but is less obtrusive and typically provides more gain than a directly connected antenna.  A dome antenna provides 360 degrees of horizontal coverage in a downward direction, making them ideal for covering a single floor with a more or less square layout.  Inside antennas can be directional as well.  If you are you looking to provide directional coverage for a large, open space or hallway, the Cellular Solutions 501135 wall-mounted panel antenna provides this.  A panel antenna can also be installed in an attic (facing downward) for single floor coverage with tall ceilings.  They may also be installed facing downward on lower ceilings for mutiple floor zoned coverage.

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 and intend on wall mounting
  • 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 zBoost and Wilson products use standard RG6 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 will provide in gain.  Remember, you want your amplifier to receive the highest quality signal possible in order to provide full indoor coverage.  For this reason, it is recommended that runs using RG6 should be no more than 60 ft. For runs longer than 60', RG11 should be used.  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)

Example Installation Diagrams




  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.

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