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# The Decibel Calculator

**The ***decibel (dB)* is the unit of relative power. If one signal is twice as loud as another, it has a gain of 3dB. One advantage of expressing power in decibels is that, in a multi-stage
amplifier, the power gains of the stages can simply be added together.
The general expression for calculating the decibel gain of a circuit (or an antenna) is:-

*Enter values for 'Power Out' and 'Power In' and press the ' = ' button.*

## dBW

The UK amateur radio licence expresses the maximum permitted output power for each band in dBW. This is the output power, in dB, relative to 1 Watt. To express this in Watts, the following
formula can be used:-

## Antenna Gain

The gain of an antenna is relative to either a theoretical, *isotropic* aerial (dBi) or relative to a half-wave dipole (dBd).

## Voltage Gain

The dB gain of one *voltage* relative to another can be calculated with the formula:-
However, the result is only correct when the input and output impedances of the circuit are the same.

73s

VU2FD