专业英语第六段的,.pptVIP

Microwave Systems Para 6 Instead of using wire or cable,microwave systems can use the atmosphere as the medium through which to transmit signals.These systems are extensively used for high-volume as well as long-distance communication of both data and voice in the form of electromagnetic waves similar to radio waves but in a higher frequency range. 微波系统 和使用导线或电缆不同，微波系统用大气作为媒介，据此传输信号。这些系统主要用于大批量及长距离的电磁波形式的数据和话音通信，类似于无线电波，但频率范围更高。 Microwave signals are often referred to as line of sight signals because they cant bend around the curvature.of the earth;instead,they must be relayed from point to point by microwave towers,or relay stations,placed 20 to 30 miles apart.The distance between the towers depends on the curves about 8 inches every mile.The towers have either a dish or a horn-shaped antenna. 微波信号通常是指直线信号，因为它们不能随地球的弯曲而弯曲；相反地，它们必须由微波塔或每20~30英里设置的中继站实现点到点的转发。俩座塔之间的距离取决于附近地表的弯曲程度。地球表面通常每英里弯曲8英寸。微波塔有一个截抛物面天线或一个圆锥形天线。 The size of the antenna varies according to the distance the signals must cover.A long-distance antenna could easily be 10 feet or larger in size;a dish of 2to4 feet in diameter,which you often see on city buildings,is large enough for short distances.Each tower facility receives incoming traffic,boosts the signal strength,and sends the signal to the next station. 天线的长度随信号需要覆盖的距离范围而变化。一个长距离天线可达10英尺或更长；直径在2~4英尺的截抛物面天线对短距离的转发已经足够了，这种天线在城市建筑物顶上能经常看到。塔上的设备将接收过来的信号并对其加以放大，把信号发送到下一个基站。 * *