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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク signal strength ： ウィキペディア英語版 signal strength In telecommunications, particularly in radio, signal strength refers to the magnitude of the electric field at a reference point that is at a significant distance from the transmitting antenna. It may also be referred to as received signal level or field strength. Typically, it is expressed in voltage per length or signal power received by a reference 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). ;Examples: *100 dBµ or 100 mV/m: blanketing interference may occur on some receivers *60 dBµ or 1.0 mV/m: frequently considered the edge of a radio station's protected area in North America *40 dBµ or 0.1 mV/m: the minimum strength at which a station can be received with acceptable quality on most receivers ==Relationship to average radiated power== 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 :$$ E_\theta (r) = e^ where $\backslash scriptstyle$ is the angle between the antenna axis and the vector to the observation point, $\backslash scriptstyle$ is the peak current at the feed-point, $\backslash scriptstyle$ is the permittivity of free-space, $\backslash scriptstyle$ is the speed of light in a vacuum, and $\backslash scriptstyle$ is the distance to the antenna in meters. When the antenna is viewed broadside ($\backslash scriptstyle$) the electric field is maximum and given by :$$ \vert E_(r) \vert = \, . Solving this formula for the peak current yields :$$ I_\circ = 2\pi\varepsilon_\circ c \, r\vert E_(r) \vert \, . The average power to the antenna is :$R\_a\; \backslash ,\; I\_\backslash circ^2\; \}$ where $\backslash scriptstyle$ is the center-fed half-wave antenna’s radiation resistance. Substituting the formula for $\backslash scriptstyle$ into the one for $\backslash scriptstyle(r)\backslash vert\; \backslash ,\; =\; \backslash ,$ \sqrt \, = \, \sqrt \quad (L = \lambda /2) \, . Therefore, if the average power to a half-wave dipole antenna is 1 mW, then the maximum electric field at 313 m (1027 ft) is 1 mV/m (60 dBµ). For a short dipole ($\backslash scriptstyle$) the current distribution is nearly triangular. In this case, the electric field and radiation resistance are :$$ E_\theta (r) = \left ( \right ) e^ \, , \quad R_a = 20\pi^2 \left ( \right )^2 . Using a procedure similar to that above, the maximum electric field for a center-fed short dipole is :$$ \vert E_(r)\vert \, = \, \sqrt \, = \, \sqrt \quad (L \ll \lambda /2)\, . 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「signal strength」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.