| 摘要 |
1,253,508. Repeating dialled impulses. GNT AUTOMATIC A.S. 14 Sept., 1970 [19 Sept., 1969], No. 43802/70. Heading H4K. A transistor oscillator Q1 in shunt across a telephone line is switched into oscillation by each loop-disconnect impulse as detected by a resistor R3 in one leg of the line. The collectoremitter path of transistor Q1 shunts the legs La, Lb, of a loop between impulsing contacts 3 and feedbridge relay windings 1. The collector circuit is tuned by L1, C2, and feedback is provided by L2, C3, R2. Shunt capacitor C2 keeps A.C. off the line and Zener Z1 takes overvoltages. The closed and open loop condition is reflected in voltage across R3 which switches Q3 on and off accordingly so that oscillator Q1 is driven in response to each loop disconnection. Output in winding L3 switches transistor Q2 to repeat the impulses. The oscillator may be switched on and off by a diode shunt circuit round resistor R3 as an alternative to transistor Q3, Fig. 1, not shown. Oscillator current is limited by resistor R1 or by a constant current diode. |
