The dictionary explanation of a decibel (dB) is that it is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power or intensity) relative to a specified or implied reference level. Since it expresses a ratio of two quantities with the same unit, it is a dimensionless unit. A decibel is one tenth of a bel (B).

 

 

The output of RF output Directional Couplers is expressed in DB. For example 10db = 10:1

In other words if an RF coupler has 1 watt out of the incident probe, the main line has 10 watts. By calibrating the coupler to your needs, say 39 DB the ratio would be 8000:1. In that case you would multiply the reading of the watt meter by 8000 to get your mainline power.

 

 

  3dB =               2:1

10dB =             10:1

20dB =           100:1

30dB =        1,000:1

40dB =      10,000:1

50dB =    100,000:1

60dB = 1,000,000:1

 

50dB = 100,000:1

53dB = 200,000:1

56dB = 400,000:1