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我国中同轴1800路载波通信系统工作方式是同频四线制,即需要一根同轴电缆中的两个同轴管,分别供来去两方向传输之用,使用同一的传输频谱、线路频谱都是从308KHZ至9008KHZ.此系统的1800路电话的线路频谱,全由标准的12路基群(60～108KHZ)60路超群(312～552KHZ),部分是由标准的300路主群(812～2044KHZ)经过多级调制程序而组成.每一电话通路的有效传输频带是从300～3400HZ,简称4KHZ频带,每路振铃信号是2100HZ.
Coaxial 1800 Road, China’s carrier communication system working mode is the same frequency four-wire system, which requires a coaxial cable in the two coaxial tubes, respectively, for both to and from the transmission, the use of the same transmission spectrum, lines Spectrum is from 308KHZ to 9008KHZ.The line frequency spectrum of 1800 telephone of this system is composed of standard 12 road group (60 ~ 108KHZ) 60 road supergroup (312 ~ 552KHZ), partly by the standard 300 road main group (812 ~ 2044KHZ) through the multi-level modulation procedures and composition of each phone channel effective transmission band from 300 ~ 3400HZ, referred to as 4KHZ band, each ring signal is 2100HZ.