In fact, a four - wire circuit can be established without the use of any wires at all, as in the case with a circuit established over microwave, satellite, or infrared transmission systems.
事实上，可以不使用任何线来建立四线电路，例如通过微波、卫星或红外传输系统。
Footprint - the area in which a specific transmission can be received. Some footprints cover as much as one-third of the earth, such as satellite or cell systems.
覆盖面-某个卫星信号覆盖的区域。有些卫星信号覆盖面非常大，达整个地球的三分之一，例如卫星或手提电话系统等。
It has a satellite communications and transmission network, and has introduced 10 computerized information processing systems.
它有一个卫星通信和传输网络，并引进了10个计算机信息处理系统。
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