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根据电子工业部与总参通信部的有关协议和合同,由电子部有关单位承担的北京23公里光缆传输系统,已于1985年9月9日全线开通。该系统开通时暂传120路PCM电话(即二次群)和双向彩色电视,无中继传输距离23公里,为目前国内无中继距离最长的长波长光缆通信系统。由于系统余量很大,在开通过程中把光路延长到52公里时,PCM二次群系统还能正常工作,误码率小于1×10~(-9);把光路延长到30公里,PFM调制彩电传输系统仍有5dB以上的系统功率余量,系统完全能正常地工作;10月18日在23公里
According to the relevant agreement and contract of the Ministry of Electronics Industry and the General Staff Ministry of Communications, the 23 km optical cable transmission system in Beijing undertaken by the relevant departments of the Ministry of Electronics has been fully opened on September 9, 1985. When the system is opened, it temporarily transmits 120 PCM telephones (that is, secondary groups) and two-way color televisions without relay transmission distance of 23 km. It is the long-wavelength optical fiber cable communication system with the longest relayless distance in China at present. Due to the large system margin, when the optical path is extended to 52 km in the process of opening, the PCM secondary group system can work normally with the bit error rate less than 1 × 10 -9. The optical path is extended to 30 km and the PFM Modulation TV transmission system is still more than 5dB system power headroom, the system can work properly; October 18 at 23 km