GB644571A - Telecommunication exchange - Google Patents

Abstract

644,571. Electric control systems. STANDARD TELEPHONES & CABLES, Ltd. Nov. 4, 1946, No. 32708. Convention date, Nov. 14, 1945. [Class 38 (iv)] [Also in Groups XXXIX, XL (a), XL (b), and XL (c)] In an automatic telephone system (see Group XXXIX) in which it is desired to select pulses derived from any one of a plurality of electrodes 49-68 of a cathode-ray distributer 39 (see Group XL (a)), a local oscillator of natural frequency slightly different from the scanning frequency (10 kc.) of the distributer is caused to lock in synchronism with the wanted incoming pulses. When a D.C. loop is closed through a calling subscriber's equipment 21, secondary electrons, emitted when the beam falls on the electrode 53, are collected by the anode 69 to produce a pulse in wire 71 which after inversion and clipping off the modulation is applied to the grid of valve 88. A local oscillator 198 after frequency dividing produces pulses of frequency slightly less than 10 kc. which are applied through amplifier 95 to the cathode of valve 88. When the two pulses applied to 88 are in phase, 88 conducts to produce pulses 100 which are integrated and applied to open a gate 203, 205 to admit a current from a master 200 kc. oscillator to the local oscillator which is thus locked to synchronize the two pulses applied to valve 88. The pulses 100 are also integrated and applied to cut off valve 105, thereby increasing the bias and consequent amplification of valve 95. The pulses thus applied to the cathode of 88 are increased and the valve 88 runs into grid current, thereby restricting the amplitude of pulses on wire 27 so as not to cause the lock-in of the local oscillators of other similar circuits connected to wire 27. The pulses 100 are also applied to the gate 108 to pass modulated pulses received over wire 28 to a utilization circuit over wire 33. In a modification, Fig. 12 (not shown), the 10 kc. pulses 100 are used directly to lock-in the 200 kc. local oscillator and in a further modification, Fig. 6 (not shown), the pulses 100 lock-in directly a 10 kc. local oscillator.