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.
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:-
The gain of an antenna is relative to either a theoretical,
isotropic aerial (dBi) or relative to a half-wave dipole (dBd).
For any given antenna, the isotropic gain is 2.1 dB greater than the
dBd figure so...
dBd = dBi - 2.1 or...
dBi = dBd + 2.1
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.
73 from John G4VWL @GB7DEE email: [email protected]
This page was found on Packet Radio. If you find it useful send thanks to John (G4VWL)