Appendix C

Useful tables and formulae

C.1 The deciBel

The deciBel (dB) represents a logarithmic ratio between two quantities. Of itself it is unitless. If the ratio is referred to a specific quantity (P2, V2 or l2 below) this is indicated by a suffix, e.g. dBμV is referred to 1μV, dBm is referred to 1mW.

Common suffixes

suffix refers to suffix refers to
dBV 1 volt dBA 1 amp
dBmV 1 millivolt dBμA 1 microamp
dBμv 1 microvolt dBμA/m 1 microamp per metre
dBV/m 1 volt per metre dBW 1 watt
dBμV/m 1 microvolt per metre dBm 1 milliwatt
    dBμW 1 microwatt


Originally the dB was conceived as a power ratio, hence it is given ...

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