This paper introduces a kind of emergency broadcast system based on the existing AM broadcasting network and the paper also introduces the theory and technology of the system, and conducts a research into and an analysis of the operating principle of the transmitter, receiving part and emergency switch part of the system. The system does not need to make any changes to the equipment of medium wave radio station. Digital base band signal is transmitted through computer processing in the form of pre-COFDM modulation in multiple or?thogonal subcarriers, directly synthesized into the radio audio input port and transmitted by radio after modula?tion and power amplifier. As long as they are within the radio service area, the required texts or pictures can be obtained via ordinary radio receiver receiving frequency corresponding to the medium wave broadcast, and after the demodulation of the computer software. Considering the credibility of the broadcast and the one-way sealing, the information channel is safe and reliable, and false information cannot be invaded, and it is expected to be?come the reliable and regular channel of receiving emergency information.%介绍一种基于现有的中波调幅广播网络的应急广播系统,该系统无需对中波广播电台的设备进行任何改动. 被传送的数字基带信号,通过计算机处理以COFDM方式预调制在多个正交子载波上,合成后直接送入广播电台的音频输入口,经调制和功率放大后广播发射;只要在广播电台服务区内,利用普通收音机接收相应频率的中波广播,经计算机软件解调后就能得到需要的文字或图片. 由于广播的公信力和单向封闭性,该信息渠道安全可靠,虚假信息无法侵入,有望成为接收应急信息的可靠正规渠道.
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