PURPOSE: To detect accurately disconnection of transmission line by adding a data demodulated into a data of a Code Mark Inversion (CMI) code to a tank circuit turned respectively to a frequency of the original code speed or twice the original code speed, extracting, rectifying and adding the frequency component respectively so as to detect the disconnection of transmission line.
CONSTITUTION: When "1" of the CMI code is inputted to a tank circuit 2 and "0" of the CMI code is inputted to a tank circuit 3, each frequency component is extracted respectively, rectified at rectifiers 4, 5, added at an adder circuit 6 and inputted to a comparator 7. When the circuit is normal, any of the tank circuits 2, 3 outputs the frequency component without fail and an output of the adder circuit 6 is a prescribed value. When the transmission line is disconnected, the data formed into he CMI code is not inputted to a buffer amplifier 1, the frequency component extracted by the tank circuits 2, 3 is small, the output of the adder circuit 6 turns to a low level and an output of the comparator 7 turns to L level. Thus, the disconnection of the transmission line is detected.
HANAOKA SUSUMU
TAKADA KUNIO
ICHIKAWA AKIHIKO
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