Effective radiated power
In radio telecommunications, effective radiated power or ERP is determined by subtracting system losses from system gains. ERP is typically applied to antenna systems. For example, if an antenna system has +9dB gain and −6dB loss, its ERP is +3dB over the transmitter power output (TPO).
For example, an FM radio station which advertises that it has 100,000 watts of power actually has 100,000 watts ERP, and not a 100,000-watt transmitter. The TPO of such a station is most likely around 10,000-20,000 watts, with a gain of +7 to +10dB (5× to 10×). In addition, if the antenna is directional, the ERP figure is usually the maximum in any one direction, rather than the average.
ERP is always relative to a reference antenna. A dipole antenna is most often used, but an imaginary isotropic antenna which radiates equally in all directions may also be used.
From FS-1037C:
Effective radiated power:
1. 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 (used by the NTIA and FCC).
- Note: If the direction is not specified, the direction of maximum gain is assumed.
Effective isotropically-radiated power (EIRP):
The arithmetic product of (a) the power supplied to an antenna and (b) its gain relative to an isotropic source.
