MONITOR SYSTEM OF DIGITAL RELAY TRANSMISSION LINE

摘要

PURPOSE:To prevent a transmission line during communication from forming a folding connection loop, by inhibiting the forming of the folding connection loop, when a communication exists on a communication line of opposite direction. CONSTITUTION:A monitor 3 transmits a specific frequency obtained by generating a random pulse train signal from a pulse generator 11 to each repeater. The repeater 4 extracts the specific frequency at a monitor frequency extracting circuit 33 from a signal transmitted to a communication line 1 and when an output exists, a signal of the communication line 1 is folded and connected to a communication line 2 by controlling a switch circuit 37. In this case, the opposite communication line 2 is monitored at a communication signal detecting circuit 41 and so long as no communication signal exists on the communication line 2, the control of the switch circuit 37 is made effective.