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What is dBi? Print
May 2010

dBi is dB(isotropic).
It is the forward gain of an antenna compared with the hypothetical isotropic antenna.  An isotropic antenna radiates uniformly in all directions over a sphere centred at the antenna.

When the antenna is connected to a radio source, the gain is expressed in deciBel (dB).  x = 10 log10 (Po / Pi) where Po is the output power and Pi is the input power from the radio source.