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). 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 center-fed half-wave dipole antenna in free space, where the total length L is equal to one half wavelength (λ/2). If constructed from thin conductors, the current distribution is essentially sinusoidal and the radiating electric field is given by where θ {displaystyle scriptstyle { heta }} is the angle between the antenna axis and the vector to the observation point, I ∘ {displaystyle scriptstyle {I_{circ }}} is the peak current at the feed-point, ε 0 = 8.85 × 10 − 12 F / m {displaystyle scriptstyle {varepsilon _{0},=,8.85 imes 10^{-12},F/m}} is the permittivity of free-space, c = 3 × 10 8 m / S {displaystyle scriptstyle {c,=,3 imes 10^{8},m/S}} is the speed of light in a vacuum, and r {displaystyle scriptstyle {r}} is the distance to the antenna in meters. When the antenna is viewed broadside ( θ = π / 2 {displaystyle scriptstyle { heta ,=,pi /2}} ) the electric field is maximum and given by