| 摘要 |
PURPOSE:To eliminate leaked noise and to ensure the transmission and reception of voice with high quality, by transmitting a cancel pulse signal synchronized with a pulse signal to an voice signal line when a channel selection pulse signal is transmitted. CONSTITUTION:A channel selecting operation is carried out to call out the remote side, then a channel selection pulse is transmitted to a signal line 21 from a control circuit 1 through a resistance 2, a transistor TR3 and a resistance 4. On the other hand, the channel selection pulse is differentiated by a capacitor 9 and a resistance 10 of a noise eliminating circuit 5. A TR11 is instantaneously turned on, and the voltage which is hitherto divided by a resistance 12 and a variable resistance 13 is settled down instantaneously at OV. Then a negative pulse is fed to a line 22. In the same way, a noise eliminating circuit 6 feeds a positive pulse to the line 22 during the fall of the channel selection pulse. In such a way, the positive and negative cancel pulses are transmitted to the line 22 from circuits 5 and 6 to cancel the leaked noise and to eliminate noise. |
