Decibel Notation - Facts and History
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         Number of Decibels
 
        

        Relative Increase in Power
 
      
      

        

        0
 
        

        1
 
      
      

        

        1
 
        

        1.26
 
      
      

        

        3
 
        

        2
 
      
      

        

        10
 
        

        10
 
      
      

        

        20
 
        

        100
 
      
      

        

        30
 
        

        1000
 
      
      

        

        50
 
        

        100,000
 
      
      

        

        100
 
        

        10,000,000,000
 
      
    

    Alexander Graham Bell created the decibel (dB) notation as a
    means to describe the changes in amplitude between two signals.
    This notation is used in regards to the satellite industry to
    show power levels in watts, dBw. The decibel formula for watts
    is:

    Decibel Difference = 10log(Power Signal A/Power Signal B)
    where log is logarithm. Downlink EIRP (effective isotropic radiated
    power) of a satellite is rated in dBw (decibels above one watt)
    which indicates the power of the uplinked signal as compared
    to the amplification it undergoes by the satellite for return
    transmission to earth. Downlink footprint maps are contoured
    in EIRP dBw to show the expected signal strength from a satellite
    per geographic location. Link budgets use the EIRP dBw values
    in calculations for the appropriate dish size required to receive
    that signal. It is important to note that a contour difference
    of 3dBw represents a doubling (or halving as the case may be)
    of power from that satellite. In regards to a satellite dish,
    an increase of 3dB, termed an increase in gain, from one dish
    to the other (comparison of two signals) indicates that one dish
    receives twice as much signal as the other. In summary, it could
    be said that decibels allows us to express large relative changes
    between signals without having to write large numbers!!!