| 摘要 |
PURPOSE:To obtain a mobile communication circuit monitor device which is separated from the subscriber telephone set by installing the means to identify the polarity and the means to connect the monitor unit to the communication circuit via the communication circuit in which the polarity of the DC voltage becomes opposite between the communication time and the non-communication time. CONSTITUTION:When the desired called subscriber answers through calling by subscriber telephone set TERM and dialing, relay E of trunk TRK operates. As a result, the polarity of the potential reverses between wires (a) and (b) of the telephone subscriber circuit. At this monent, rectifier MR of monitor device MOM becomes conductive to operate relay ON, and then monitoring amplifier AMP is connected to the telephone subscriber circuit to secure the monitor for the aural signal on the circuit. In case TREM has the incoming, relay RTA of TRK operates to make TERM ring the bell. When TERM answers, relay RT of TRK operates to release relay RTA. Thus the polarity is reversed between wires (a) and (b). As a result, rectifier MR of the monitor conducts to operate relay ON and then secure the connection between AMP and the circuit. Thus the monitoring becomes possible for the aural signal. |
