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

image

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

Get EMC for Product Designers now with O’Reilly online learning.

O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.