GB756161A - Coded electrical signal transmission system - Google Patents

Abstract

756,161. Pulse code modulation circuits; pulse circuits. STANDARD TELEPHONES & CABLES, Ltd. Aug. 7, 1953 [Aug. 7, 1952], No. 21852/53. Classes 40 (5) and 40 (6). In a pulse code communication system wherein the transmitted pulses represent changes in signal amplitude, and are taken from a train of regularly-repeated pulses, the recurrence frequency of a second pulse train is modulated by a signal wave and a code pulse is transmitted corresponding to each pulse from the first train which follows next after a pulse in the second. In order so that the transmitted pulses should represent changes in signal amplitude, the modulating wave is derived from the original signal wave at terminal 11, Fig. 3, by differentiation in circuit 12, 13. It is applied to the grid of the blocking oscillator 14, 15 through the cathode follower stage 16 and varies the oscillator recurrence frequency. The modulated pulses in transformer 15 are applied to a two-stability trigger circuit 17 to change its state from A to B. The regularly repeated pulses from terminal 18 are applied to circuit 17 to change its state from B to A. The latter change produces a code pulse at the output terminal 20 from a differentiating and amplifying circuit 19 connected to circuit 17, that is whenever a pulse at 18 immediately follows a pulse from 15. Circuit 17 may alternatively comprise a normally non-conducting rectifier 34, Fig. 5, the bias on which is too great to be overcome by the regularly-repeated pulses applied thereto from terminal 31, through rectifier 33 and condenser 35, unless in the preceding interval one of the modulated pulses applied to terminal 30 has charged condenser 35 through rectifier 36. Specification 627,462 is referred to.