| 摘要 |
PURPOSE:To prevent the malfunction at the charging pulse detection, by filtering the noise from the AM broadcast waves induced on the telephone line and the pulse-like noise from the telephone stations for high band blocking, and rejecting the commercial frequency noise with BPF. CONSTITUTION:The charging pulse detection section consists of a pair of capacitors connected in series with the subscribing telephone line detecting the charging pulse from the toll telephone exchanger and of the resistance bridge blocking the communication audio signal. Further, the high blocking filters C11 and C12 reject the pulse-like noise from the noise signal and the telephone station with the electromagnetic waves of AM radio broadcasting waves between the detection section and the commerication charging cricuit 13. In addition the commercial frequency induced on the subscribing telephone lines with the commercial high voltage distribution lines is rejected through the band rejection filter 12, allowing to pass through the charging pulse with low loss. Thus, the malfunction in detecting the charging pulse can be prevented. |
