| 摘要 |
PURPOSE:To prevent the intermission of a dial tone and a call tone from being intermitted and to eliminate the anxiety, by bringing a switching device into the receiving state while a called party responds to the transmission, in the a device switching a transmitting or the receiving state with a variable loss circuit. CONSTITUTION:In closing a telephone line for the transmission, a dial tone (400Hz) is detected at a dial tone detecting circuit 9. When the dialing is performed, the dial tone is lost, the dial tone detecting circuit 9 is turned off, but a dial tone detection circuit 10 is turned on. When a called party is called, a call tone is transmitted from a telephone line and detected at a call tone detection circuit 11. Each detecting output of the dial tone detecting circuit 9, dial detecting circuit 10, call tone detecting circuit 11 and a busy tone detecting circuit 12 is applied to a start control circuit 13, and since a control circuit 8 is operated to bring the state into the receiving state while the called party responds after calling, no anxiety is given to the user. |
