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Low frequency telephony pulse detector - detects test signal in synchronism with strong active signal presence
Low frequency telephony pulse detector - detects test signal in synchronism with strong active signal presence
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机译:低频电话脉冲检测器-与强大的活动信号存在同步地检测测试信号
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摘要
The circuit is used in telephony when line checking at 50Hz and 450Hz. The locally generated signal at high level is connected to a bridge rectifier (D4-7) and it provides the supply to a transistor detector stage (T5). The test signal after attenuation through line equipment is amplified and squared (T1, T2) and slaves a monstable multivibrator (T3, T4). This square-wave passes to the detector and if the stage is active (i.e. the high level signal is present) a diode and capacitor circuit (D2, C7) links it to an output transistor that provides an output signal and energises a light-emitting diode. This circuit protects against false readings caused by parasitic voltages by its system of coincidence detection.
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