In telecommunication, the term absolute gain has the following meanings:

1. Of an antenna, for a given direction and polarization, the ratio of (a) the power that would be required at the input of an ideal isotropic radiator to (b) the power actually supplied to the given antenna, to produce the same radiation intensity in the far-field region.

Note 1: If no direction is given, the absolute gain of an antenna corresponds to the direction of maximum effective radiated power.

Note 2: Absolute gain is usually expressed in dB. Synonym isotropic gain. 2. Of a device, the ratio of (a) the signal level at the output of the device to (b) that of its input under a specified set of operating conditions.

Note 1: Examples of absolute gain are no-load gain, full-load gain, and small-signal gain.

Note 2: Absolute gain is usually expressed in dB.

Source: from Federal Standard 1037C and from MIL-STD-188