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Dipole field strength in free space, in
telecommunications Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of ...
, is the electric field strength caused by a half wave dipole under ideal conditions. The actual field strength in terrestrial environments is calculated by empirical formulas based on this field strength.


Power density

Let N be the effective power radiated from an isotropic antenna and p be the power density at a distance d from this source :\mbox = \frac Power density is also defined in terms of electrical field strength; Let E be the electrical field and Z be the impedance of the free space :\mbox = \frac The following relation is obtained by equating the two, : \frac= \frac or by rearranging the terms : \mbox =\frac


Numerical values

Impedance of free space is roughly 120 \pi ~ \Omega Since a half wave dipole is used, its gain over an isotropic antenna (\mbox = 1.64 ) should also be taken into consideration, : \mbox =\frac \approx 7\cdot\frac In this equation
SI units The International System of Units, internationally known by the abbreviation SI (from French ), is the modern form of the metric system and the world's most widely used system of measurement. It is the only system of measurement with official st ...
are used. Expressing the same equation in: : kW instead of W in power, :km instead of m in
distance Distance is a numerical or occasionally qualitative measurement of how far apart objects, points, people, or ideas are. In physics or everyday usage, distance may refer to a physical length or an estimation based on other criteria (e.g. "two co ...
and :mV/m instead of V/m in
electric field An electric field (sometimes called E-field) is a field (physics), physical field that surrounds electrically charged particles such as electrons. In classical electromagnetism, the electric field of a single charge (or group of charges) descri ...
is equivalent to multiplying the expression on the right by \sqrt.K.H.Kaltbeitzer: ''Site selection'', EBU Techhnical Monograph 3104, Bruxelles, 1965, p 30 In this case, :\mbox \approx 222\cdot\frac :


See also

*
Antenna (radio) In radio-frequency engineering, an antenna (American English) or aerial (British English) is an electronic device that converts an alternating current, alternating electric current into radio waves (transmitting), or radio waves into an elect ...
* Effective radiated power *
Electric field An electric field (sometimes called E-field) is a field (physics), physical field that surrounds electrically charged particles such as electrons. In classical electromagnetism, the electric field of a single charge (or group of charges) descri ...
* Field strength meter * Radio propagation model


References

{{Radio frequency propagation models Telecommunication theory Antennas Broadcast engineering Radio frequency propagation model