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
:
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
:
The following relation is obtained by equating the two,
:
or by rearranging the terms
:
Numerical values
Impedance of free space is roughly
Since a
half wave dipole is used, its
gain over an isotropic antenna (
) should also be taken into consideration,
:
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
.
[K.H.Kaltbeitzer: ''Site selection'', EBU Techhnical Monograph 3104, Bruxelles, 1965, p 30] In this case,
:
:
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