The power supplied to an antenna multiplied by the antenna gain in a given direction. Note 1: If the direction is not specified, the direction of maximum gain is assumed. Note 2: The type of reference antenna must be specified. 2. The product of the power supplied to the antenna and its gain relative to a half-wave dipole in a given direction. Note: If the direction is not specified, the direction of maximum gain is assumed. 3. The effective radiated power of a transmitter (with antenna, transmission line, duplexers, etc. ,) is the power that would be necessary at the input terminals of a reference half-wave dipole antenna in order to produce the same maximum field intensity. ERP is usually calculated by multiplying the measured transmitter output power by the specified antenna system gain, relative to a half-wave dipole, in the direction of interest.