The Effective Isotropic Radiated Power of a transmitter (uplink) is the power that the transmitter appears to have if the transmitter was an isotropic radiator, i.e., if it radiated equally in all directions. By virtue of the gain of a radio antenna, dish, radio telescope or optical telescope, a beam is formed that preferentially transmits the energy in one direction. The EIRP is given by the product of the gain and the transmitter power.
