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Reply To: question about ant. gain and radiated ..


decibels are a weird unit 🙂 but very convenient !

dBm are absolute power, they correspond to a certain amount of mW. For instance 0dBm = 1mW, 33dBm = 2W.

dBi are relative power: they indicate how much gain is given to an input signal. It’s like the “dB”.
For instance :
0dBm + 3dB = 3dBm = 2mW
3dBm + 3dB = 6dBm = 4mW
6dBm + 3dB = 9dBm = 8mW
9dBm + 3dB = 12dBm = 16mW

As you see, 3dB is not equal to xx dBm. It is a factor which means the power (in watts) is multiplied by 2.

An antenna “multiplies” the input power by a certain factor. It’s “relative power”.