| 摘要 |
1,030,074. Substation circuit. SIEMENS & HALSKE A.G. Sept. 9, 1964 [Sept. 11, 1963], No. 36870/64. Headings H3T and H4K. [Also in Division G1] In a push-button telephone subscriber station an audio signal is given after a button has been actuated to confirm the operation of the associated digit signalling components. In one arrangement shown in Fig. 1, each button is a variable capacitor SKI ... SKn such that when the operators' finger is placed upon it the reactance falls and allows the associated glow discharge tube Gl1 ... Gln to ignite; the subsequent drop in resistance of the photosensitive resistor F1 . . . Fn actuates the digit switching relays A1 . . . An. The voltage across R2 delivered through the differentiating circuit C, D, produces a short audible signal in the station signal device T, which is connected to the keyboard on raising the switch hook contacts W1, W2. In a second arrangement, having a normal push-button keyboard (Fig. 2), the audible signal is produced by the amplifier in the subscriber station which is made to oscillate each time a button is pressed by shunting the negative feedback resistor R GK by the tuned circuit C1, L1 as the Zener diode Z breaks down. The oscillations are monitored through the receiver H and their frequency is determined by C1, L1. The break-down voltage to the diode is applied from button contacts a1 ... a0 through a differentiating circuit C D , to produce only a short signal. The buttons also actuate the digit signal relays A1 . . . A0. With no button pressed the combined effect of the negative feedback from R GK and the positive from R MK produces no oscillations and the speech signals are amplified in the normal way. |
