The Effective Isotropic Radiated Power (EIRP) is the apparent power transmitted towards the receiver, if it is assumed that the signal is radiated equally in all directions, such as as a spherical wave emanating from a point source; in other words, the arithmetic product of the power supplied to an antenna and its gain. Begin by testing the transmitter with a good dummy load and a good calibrated watt meter. Enter that value. Then enter the antenna gain. Finally, click on the Calculate button for the pure ERP and EIRP. This calculator is considering only power and antenna gain.
By definition, ERP is the abbreviation for Effective Radiated Power that is directed in a given direction. It is the power supplied to an antenna multiplied by the antenna gain in a given direction. If the direction is not specified, the direction of maximum gain is assumed and the type of reference antenna should be specified. It is also the product of the power supplied to the antenna and its gain relative to a half-wave dipole in a given direction and it is the effective radiated power of a transmitter (with antenna, transmission line, duplexers, etc.) Also, it 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.