This page defines the term "Decibel (dB)" and illustrates the measure with an example.
A dB is a ratio that we use when we are talking about power
- Pi=Power Input
- Po=Power Output
- X dB = 10Log10(Po /Pi )
Example:
A transistor has an output power of 50 watts with 10 watts input power. Its gain in dB is:10Log10(50 /10) = 10Log105 = 6.9897 ~ = 7.0 dB
and an attenuator that has an output of 25 watts with an input of 100 watts is:
10Log10(25 /100) = 10Log100.25 = -6.021 ~ = -6.0 dB