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EMC for Product Designers, 4th Edition by Tim Williams

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Appendix D Useful tables and formulae

D.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 I2 below) this is indicated by a suffix, e.g. dBμV is referred to 1μV, dBm is referred to 1mW.

Common suffixes

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

Power is proportional to voltage squared, hence the ratio of voltages or currents across a constant impedance is given by:

Conversion between voltage in ...

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