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过去,利用对流层散射的超视距通信系统,限于小容量电话传输。随着最近几年通信系统多用途的发展,对于超视距通信系统传输容量的要求也日益扩大,电话从120路扩大到300路,而且进一步扩大到传输电视信号。为了实现这些要求,日本电气公司(NEC)继续研究了采用对流层散射超视距通信系统传输电视的可能性。作为一种方法,研究了采用四重或八重中频组合的分集接收方式的超视距电视传输系统,并在实际电路上投入使用,获得了良好的结果。在向海岛、沙漠等边远地区传输电视时,可以说超视距通信同视距微波通信和卫星通信一样,也是一种在实用方面具有较好传输质量的有效方法。本文介绍的是NEC最近交付利比亚用在撒哈拉沙漠地带的超视距电视传输系统的概要和性能。
In the past, over-the-horizon communication systems using tropospheric scatter were limited to small-capacity telephone transmissions. With the multi-purpose development of communication systems in recent years, the requirements for transmission capacity of OTH communication systems have also been increasing. The number of phones has been expanded from 120 to 300 and further extended to the transmission of television signals. In order to meet these requirements, NEC continued its study of the possibility of transmitting television using a trans-horizon STO system. As a method, the over-the-horizon television transmission system adopting diversity receiving method of quadruple or octave intermediate frequency is studied and put into practical use, and good results are obtained. When transmitting television to remote areas such as islands and deserts, it can be said that OTH communication is the same as satellite communication with line-of-sight and is also an effective method with better transmission quality in practical aspects. This article describes the outline and performance of the over-the-horizon television transmission system recently delivered by NEC to Libya for use in the Sahara Desert.