| 摘要 |
PURPOSE:To avoid a call signal from being sent to a receiver of the operator by inhibiting a reception path at the detection of a call signal from an opposite side accommodated in an exchange by the ring down system. CONSTITUTION:A magnetic type telephone set (not shown) being an opposite terminal equipment is connected to a ring down system private line LN and connected to an exchange EX via a line transformer LT. The line transformer LT is connected to a 2/4-wire conversion hybrid HYB and connected to a handset of the operator of an attendant board ATT via a DA converter D/A and an AD converter A/D. A call signal from the line LN is fetched in the exchange EX via the transformer LT and detected by a BPF 5, an amplifier rectifier 5 and a comparator 7. When the signal exists, the level of the terminal 4 is brought into an L level to light a display device 9. Further, an AND circuit 8 is interrupted to inhibit the reception line between the converter D/A and the receiver.
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