| 摘要 |
PURPOSE:To attain the pleasant conference talking by constituting the 1st and 2nd balance means decreasing the bypassing of a transmission signal to a reception signal so as to be selected depending on the state, thereby keeping the side tone to a nearly constant optimum sound volume in the conventional talking state and the conference talking state. CONSTITUTION:A reception signal from the 2nd telephone line is sent to the secondary winding 8c coupled electromagnetically from a winding 8b, extracted from a connecting point between impedance circuit networks 16, 17 and fed to the receiver of a handset, from which the signal is listened to, sent to a trunk line winding 8a and given also to the 1st telephone line. Since the 5th contact 7e of a conference talking switch is closed, an impedance circuit network 16b is connected in parallel with an impedance circuit network 16a. Since two telephone lines having equal impedance are connected in parallel in terms of AC, the impedance of the telephone line of the secondary side of the low frequency transformer 8 is lowered nearly 1/2, the side tone attenuation is kept to an optimum value and the talking is attained similarly as at the conventional talking.
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