# field strength (F)

The field strength (F) is the power density of an electromagnetic wave, in which the energies of the magnetic and electric field strength sum up.

The measure of electric field strength is the ratio of the voltage to the unit of length: volts/ meter(V/m), mV/m or µV/m. An electromagnetic wave has an electric field strength of 1 V/m if it generates a voltage of one volt in an antenna with an effective length of one meter. In satellite technology, Equivalent Isotropically Radiated Power( EIRP) is used as the unit of measurement.

Unlike electric field strength, magnetic field strength (H) refers to the ratio of current to unit length: amps per meter (A/m), milliamps/meter (mA/m), microamps/meter (µA/m), or nanoamps/meter (nA/m) or nanoamps/centimeter (nA/cm). An older unit for magnetic field strength is the oersted (Oe), which can be derived from the unit A/m: 1 oersted is equal to 79.6 A/m, thus 1 A/m is equal to 0.01256 Oe. The unit Oersted is named after the Danish physicist Hans Cristian Oersted (1777 to 1851).

With isotropic radiation, the field strength of an electromagnetic wave decreases linearly with distance from the transmitter.