| 摘要 |
<p>PURPOSE:To simplify the constitution of a circuit and to miniaturize the size, by using a low-frequency signal extracting means at a monitor circuit in common for a bidirectional transmission line. CONSTITUTION:A failure retrieval signal in an incoming transmission line, e.g., is discriminated at a discriminating system 22-1 at a failure retrieval and applied to an input of a gate 45. A signal is interrupted on an outgoing transmission line and another input of the gate 45 is at ''1''. Thus, the failure retrieval signal is applied to an FF46 via the gate 45, a low-frequency signal is reproduced and when the signal frequency is coincident with a frequency f1 assigned to the own device, an output is generated from a comparator 42, a gate 44 is opened and the failure retrieval signal is returned to the outgoing transmission line via a reproducing system 24-2. Since the gate 45 is provided in this way, the FF46 and an amplifier 47 are used in common to both the relay transmission lines to control the detection of the failure retrieval signal and the return.</p> |
