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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 Discontinuity (transmission lines) ： ウィキペディア英語版 Reflections of signals on conducting lines A signal travelling along an electrical transmission line will be partly, or wholly, reflected back in the opposite direction when the travelling signal encounters a discontinuity in the characteristic impedance of the line, or if the far end of the line is not terminated in its characteristic impedance. This can happen, for instance, if two lengths of dissimilar transmission lines are joined together. This article is about signal reflections on electrically conducting lines. Such lines are loosely referred to as copper lines, and indeed, in telecommunications are generally made from copper, but other metals are used, notably aluminium in power lines. Although this article is limited to describing reflections on conducting lines, this is essentially the same phenomenon as optical reflections in fibre-optic lines and microwave reflections in waveguides. Reflections cause several undesirable effects, including modifying frequency responses, causing overload power in transmitters and overvoltages on power lines. However, the reflection phenomenon can also be made use of in such devices as stubs and impedance transformers. The special cases of open circuit and short circuit lines are of particular relevance to stubs. Reflections cause standing waves to be set up on the line. Conversely, standing waves are an indication that reflections are present. There is a relationship between the measures of reflection coefficient and standing wave ratio. ==Specific cases== There are several approaches to understanding reflections, but the relationship of reflections to the conservation laws is particularly enlightening. A simple example is a step voltage, $\backslash scriptstyle\; Vu(t)$ (where $\backslash scriptstyle\; V$ is the height of the step and $\backslash scriptstyle\; u(t)$ is the unit step function with time $\backslash scriptstyle\; t$), applied to one end of a lossless line, and consider what happens when the line is terminated in various ways. The step will be propagated down the line according to the telegrapher's equation at some velocity $\backslash scriptstyle\; \backslash kappa$ and the incident voltage, $\backslash scriptstyle\; v\_\backslash mathrm\; i$, at some point $\backslash scriptstyle\; x$ on the line is given by〔Carr, pages 70–71〕 :$v\_\backslash mathrm\; i\; =\; Vu(\backslash kappa\; t-x)\backslash ,\backslash !$ The incident current, $\backslash scriptstyle\; i\_\backslash mathrm\; i$, can be found by dividing the characteristic impedance, $\backslash scriptstyle\; Z\_0$ :$i\_\backslash mathrm\; i\; =\; \backslash frac\; =\; Iu(\backslash kappa\; t-x)$ 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「Reflections of signals on conducting lines」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.