Equivalent Isotropically Radiated Power

In radio communication systems, equivalent isotropically radiated power (EIRP) or, alternatively, effective isotropically radiated power is the amount of power that a theoretical isotropic antenna (which evenly distributes power in all directions) would emit to produce the peak power density observed in the direction of maximum antenna gain. EIRP can take into account the losses in transmission line and connectors and includes the gain of the antenna. The EIRP is often stated in terms of decibels over a reference power emitted by an isotropic radiator with an equivalent signal strength. The EIRP allows comparisons between different emitters regardless of type, size or form. From the EIRP, and with knowledge of a real antenna's gain, it is possible to calculate real power and field strength values.

where and (output power of transmitter) are in dBm, cable losses is in dB, and antenna gain is expressed in dBi, relative to a (theoretical) isotropic reference antenna.

This example uses dBm, although it is also common to see dBW.

Decibels are a convenient way to express the ratio between two quantities. dBm uses a reference of 1 mW and dBW uses a reference of 1 W.

and

A transmission output of 50 W is the same as 17 dBW or 47 dBm.

The EIRP is used to estimate the service area of the transmitter, and to coordinate transmitters on the same frequency so that their coverage areas do not overlap.

In built-up areas, regulations may restrict the EIRP of a transmitter to prevent exposure of personnel to high power electromagnetic fields, however EIRP is normally restricted to minimise interference to services on similar frequencies.

Famous quotes containing the words equivalent and/or power:

    I started off rapping for people just like myself, people who were in awe of wealth and flash. It was a conversation between me and them. But now most of those who buy my records are listening in on others’ conversation. They are the aural equivalent of voyeurs, thrilled at this crazy world that has nothing to do with their experience.
    Ice-T [Tracy Marrow], U.S. rap musician. Observer (London, Oct. 27, 1991)

    There is a Restlessness springing from the consciousness of power not fully utilized, which must be present wherever there is unused power of whatever kind. This is the restlessness of the germ within the seed, struggling upward and downward towards its proper life. ... it is a striving full of pain, the cutting of tender flesh by the fetters of the captive as he struggles against their pitilessness.
    Anna C. Brackett (1836–1911)