Signal strength

In telecommunications, particularly in radio frequency, signal strength (also referred to as field strength) refers to the transmitter power output as received by a reference antenna at a distance from the transmitting antenna. High-powered transmissions, such as those used in broadcasting, are expressed in dB-millivolts per metre (dBmV/m). For very low-power systems, such as mobile phones, signal strength is usually expressed in dB-microvolts per metre (dBµV/m) or in decibels above a reference level of one milliwatt (dBm). In broadcasting terminology, 1 mV/m is 1000 µV/m or 60 dBµ (often written dBu).

The electric field strength at a specific point can be determined from the power delivered to the transmitting antenna, its geometry and radiation resistance. Consider the case of a bruh distribution is essentially sinusoidal and the radiating electric field is given by

where ${\displaystyle \scriptstyle {\theta }}$ is the angle between the antenna axis and the vector to the observation point, ${\displaystyle \scriptstyle {I_{\circ }}}$ is the peak current at the feed-point, ${\displaystyle \scriptstyle {\varepsilon _{\circ }\,=\,8.85\times 10^{-12}\,F/m}}$ is the permittivity of free-space, ${\displaystyle \scriptstyle {c\,=\,3\times 10^{8}\,m/S}}$ is the speed of light in a vacuum, and ${\displaystyle \scriptstyle {r}}$ is the distance to the antenna in meters. When the antenna is viewed broadside (${\displaystyle \scriptstyle {\theta \,=\,\pi /2}}$) the electric field is maximum and given by

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