| 摘要 |
<p>PURPOSE:To prevent malfunction of a monitor and control circuit due to a service signal by providing the input part of the monitor and control circuit with a gate which cuts off the input of the monitor and control circuit when a monitor and control signal is not inputted. CONSTITUTION:While the service signal is supplied to up and down transmission lines, the output of a signal break detecting circuit 5-3 in a down repeater is in the low level, and a gate 7-6 is closed. Consequently, the service signal output of an up repeater receiving part 2-1 cannot pass the gate 7-6, and frequency components of the monitor and control signal are not applied to a monitor and control part 7-3 through a monitor filter 7-2 even if these frequency components are included in the service signal, and therefore, malfunction of a monitor and control circuit 7 is not caused during service. If troubles occur on a transmission line, the service signal is turned off, and the monitor and control signal is supplied from a transmitting part 1 of a terminal station A to the up transmission line. Thereafter, loop back transmission lines are formed successively in individual repeating stations to perform test, thereby discriminating faulty positions.</p> |
