A person trained in this field may need to know how to set up and maintain telephone equipment, voicemail systems, fiber optic and microwave communication links, as well as mobile radio equipment.

在这个方面受过训练的人可能要知道如何和维护电话设备、语音信箱系统、光纤和微波通信线路，以及移动通信设备。

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However, for the wireless mobile communication systems, the radio channel is frequency selective and time-varying.

对于无线通信系统，无线信道不仅是频率选择性的，而且是时变的。

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The site is home to transmitters for most of the city's television stations, as well as some radio stations, several mobile phone companies and police communication systems.

VOA: standard.2009.09.01