通信介质就是在通信系统中位于发送端与接收端之间的物理通路。通信介质一般可分为导向性和非导向性介质两种。导向性介质有双绞线、同轴电缆和光纤等,这种介质将引导信号的传播方向;非导向性介质一般通过空气传播信号,它不为信号引导传播方向,如短波、微波和红外线通信等。
以下仅简单介绍几种常用的导向性通信介质。
1.双绞线
双绞线是一种廉价而又广为使用的通信介质,它由两根彼此绝缘的导线按照一定规则以螺旋状绞合在一起的,如图7-2所示。这种结构能在一定程度上减弱来自外部的电磁干扰及相邻双绞线引起的串音干扰。但在传输距离、带宽和数据传输速率等方面双绞线仍有其一定的局限性JOY 601849 124 230 270V Miner Mining Machine Firing Package RP100201437
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