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Calculating Coverage Area


How To Calculate A Cellular Signal Booster's Coverage Area

To calculate the estimated coverage area of a building cellular repeater system, a minimum of 4 pieces of information is required:

  1. Cellular Frequency your device is receiving from your service provider at your location.
  2. Outside Signal Strength - Received Signal Strength Level
  3, Approximate length and type of coax cable required
  4. Cellular Amplifier Gain

We can help you better calculate cellular repeater area coverage using the gain of different cellular amplifiers with this information.

Other pieces of information are helpful such as what might be blocking your cell signal such as trees, hills or just distance from the nearest tower. Also the layout of the building and factors that might be an issue running cable throughout the building such as wall types, utility closets, passage ways, etc.signal booster diagram

Video - Signal Booster Installation

Before starting, you may want to view a video of a typical system installation. You can find it on our web site at: Building Signal Booster Installation

Step 1. Determine Cellular Frequency

Determine what frequency your service provider is using in your area. Typically, your mobile phone or data card will work on multiple frequencies but your provider will only be using 1 frequency in the area your building is in. It will usually be in the range of 800MHz (including 850GSM), 1900MHz or Nextel iDen 800MHz.. We can estimate both for you if you cannot get the specific frequency being used in your area. Contact your service provider's customer service or one of your service provider's local outlets for help.


Step 2. Get Received Signal Strength Reading

received-cellular-signal-strength.jpgThe best way to get your Received Signal Strength Reading is to put your cell phone into test mode (or status mode) or get a signal reading from your cellular data card software. The reading will be in -xx db (ex -88 dbm) or similar format. A good signal would be -55db and a poor signal would be -105db as examples. More Cellular Signal Reading Info

Number of Bars - Although we can guess coverage area with the number of bars, number of bars is not at all accurate or consistent from phone to phone or service to service. 3 bars on one phone may be much weaker a signal than 3 bars on another phone. Take this reading outside the building preferably at a location where you can mount an outside antenna such as the roof on the same side of your building your service provider's tower may be.

Find Signal Reading - Phone Test Modes / Status Modes

Android Phones - To get the Received Signal Strength Reading (dBm Reading) on most Android phones, find the STATUS function. It should be exactly like or something similar to: On your device Select SETTINGS -> ABOUT PHONE -> STATUS -> Now scroll down and find "Signal Strength". You may see a 1X Signal Strength, 3G, EVDO and/or 4G Signal Strength depending on device and services provided by your cell company in your area.

On other Android devices the sequence may be SETTINGS -> MORE OPTIONS (or MORE SETTINGS) -> ABOUT PHONE -> MOBILE NETWORKS -> SIGNAL STRENGTH.

You can also download apps like “Network Signal Info” in the Google Play store to measure signal strength.

It may take some menu searching on your Android device but you should be able to find the dBm reading. If that still doesn't get you there, check your device's user manual. You may also try web searching for the "field test mode" or "signal reading" for your particular device's make and model.

BlackBerry's - To get the Signal Strength on a BlackBerry, Select TOOLS -> SETTINGS -> STATUS or OPTIONS -> STATUS

iPhone's - To put an iPhone into Test Mode - In phone mode dial *3001#12345#* then press CALL. The Field Test Screen will appear. It might display "Test Mode". The signal bars in the upper left hand corner of you screen should now change to display the signal strength reading. When testing phones in a 3G environment it is possible to determine the frequency being used by selecting: UMTS Cell environment, then select UMTS RR info. The screen display will list the Up link and down link Frequency in code form. Up link frequency on the 850 MHz cellular band will list an Up link Frequency code between 4132 and 4233 and a Down link Frequency code between 4357 and 4458. If you are operating on the 1900 MHz spectrum the Up link Frequency code will be between 9262 and 9538 with the Down link Frequency code being between 9662 and 9938.

Other Devices - For other device, use the pdf document "Standard Phone Test Modes " which has instructions for putting other cell phones into test mode and reading Received Signal strength. If your mobile phone is not listed in this document or you need additional help getting a RSSL reading, contact Wilson Electronics tech support for help at 866-294-6996. If you have a mobile broadband data card, the software will indicate signal strength either on the main screen or there's a menu option somewhere else. The cellular frequency being used may not be the same on both a data card and a cell phone. For example, you cell phone may be using 850MHz and your data card may be using 1900MHz in the same area. You won't be able to put some phones into test mode including many GSM phones from AT&T and T-Mobile. If a phone that can be put into test mode is not available, we can estimate signal strength by the number of bars of signal on a phone however, this method is not very accurate.

Tower Locations

It may help to be able find towers for your service provider(s) in your area. You can use websites like antennasearch.com or cellreception.com to get a pretty good idea of tower locations.

Signal Reading

Signal strength, measured in decibels (dB), is expressed as a negative number. On certain phones, the number may show as positive in test mode. In such cases, convert it to negative. For example, 60 dB is actually -60 dB. The higher the number, the stronger the signal. Thus, -60 dB is a stronger signal than -75 dB. A -100db is very weak signal. Contact Wilson Electronics Technical Support Department at 866-294-1660 if you have questions, or if you need assistance with the test mode of your cell phone.

If a phone you can put into test mode is not available, the following can be used as a guide with some amount of accuracy. Remember, getting a phone you can put into test mode is always best.

    o   1 bar   -101db
    o   2 bars  -100db
    o   3 bars  -99db
    o   4 bars  -98db
    o   5 bars – can be anywhere from -50db up to -97db

Verizon and Sprint
    o   2 bars -90 or better
    o   Full bars -85 and up

Less Than 3 Bars

Note that less than 3 bars of signal outside, where you mount an outside antenna, usually means you will not get much coverage area with any amplifier by itself. You'll have to stand next to or put your device right on the inside antenna to get cellular signal improvement.

Step 3. Estimate Antenna / Cabling Needs


  • Decide on which outside and inside(s) antennas you will be using. Directional antennas have higher gains and typically perform better but must be pointed at your service provider's nearest tower.
  • Estimate where you will locate the outside antenna, amplifier/repeater (located near an AC outlet) and inside antennas.
  • Calculate the cable lengths required to connect the outside antenna with the amplifier/repeater.

Concrete or metal interior walls will block the signal transmitted by inside antennas so determine if additional inside antennas and a splitter might be required. Sheet rock and studs (wood or metal) should not effect signal much if any. Calculate the cable lengths required to connect the inside antennas (and splitters if required) to the amplifier/repeater.

Tech Tip - Antenna Separation

For a successful installation, it's critical that minimum required separation distance is maintained between the inside and outside antennas. If the two antennas (outside and inside) are too close, oscillation (or feedback) will occur and the Wilson signal booster will then automatically reduce power or shut down completely to protect the cellular network from interference. Always read the install guide, and if you have any questions about required separation distance between antennas, contact us.

Step 4. Calculate Coverage Area

Using the formula:

Improved Signal Strength Distance = Amp Gain + RSSL + Cable Factor + Splitter Factor + Antenna Factor

Use the manual calculation guide below to determines approximate coverage area (distance from interior antenna(s). Cable, Splitter and Antenna factors. Use this guide to determine estimated coverage area using Wilson amplifier / repeaters. It provides the formula for estimating coverage considering factors such as Received Signal strength outside of building, length and type of cable, antenna type and splitters used.

Manual Coverage Calculation

Use the following formula to calculate your Signal Strength (S). Write in your numbers as appropriate. Be sure to account for the length of all cable, inside and out. Add up the numbers for all taps and/or splitters (if you are not using any, enter 0). Remember, AG and AF will be positive numbers; OSL, CF, TF, SF and S will be negative.

____  _____  _____  _____  _____ _____ = _____

OSL +   AG +      AF +     CF +     SF +     TF    =     S

OSL - Outside Signal Level, AG - Amplifier Gain, AF - Antenna Factor, CF - Cable Factor, SF - Splitter Factor, TF - Tap Factor

Once you have calculated your signal strength, use the graph below to determine approximate coverage distance. See below for a sample calculation.

Component Factor Conversions

Using the table below, find and circle the appropriate decibel (dB) numbers that correspond to the equipment in your particular system. Be sure to choose your numbers from the appropriate frequency column based on the service you receive (iDEN, Cellular or PCS).



Sample Signal Strength and Coverage Calculation

This example assumes an OSL of -90, use of a 60 dB cellular amplifier, an 806-939 MHz Yagi antenna and a low profile inside antenna with 100 total feet of inside and outside LMR 400 cable with no splitters or taps.

OSL -90 (always a negative number) found on cell phone in test mode

AG +60 gain

AF +16 dB gain (+13 dB for the Yagi antenna and +3 dB for the low-profile antenna)

CF -7 dB loss

SF 0 (none used)

TF 0 (none used)

Formula: -90 + 60 + 16 + -7 + 0 + 0 = -21

With a signal strength of -21, coverage distance would be approximately 120 feet from the inside antenna.


Need More Help?

Once you've gathered the information above, we can better help design a system that's right for you. Feel free to Contact us if you have questions or need additional help calculating coverage area.

Coverage Chart


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