在铁路自控、遥控技术中,利用钢轨作为传递信息的通道是一种既简便,又可节省投资的手段。一些欧美国家在70年代发展了电子计轴器(见本刊1985年第12期)及音频无绝缘轨道电路。随着铁路自控、遥控技术的发展,需通过钢轨传递的信息量也逐步增加,于是在80年代又发展了脉码调制式音频轨道电路。 In railroad self-control and remote control technology, the use of rails as a channel for transmitting information is a convenient and investment-saving measure. Some European and American countries in the 1970s developed the electronic axle counting device (see the issue of No. 12, 1985) and audio without insulated track circuit. With the development of railway automatic control and remote control technology, the amount of information to be transmitted through the railways has also gradually increased, so that in the 1980s, a pulse code modulated audio track circuit was developed.