GB583799A - Improvements relating to pulse modulated transmission systems - Google Patents

Abstract

583,799. Pulse modulation. STANDARD TELEPHONES & CABLES, Ltd., CHATTERJEA, P. K., and SCULLY, C. T. Aug. 7, 1942, No. 11098. [Class 40 (v)] In a duration-modulated pulse transmitter, means are provided for shortening the duration of the pulses before transmission so that the shortest pulse is always reduced to a desired minimum and all other pulses are shortened by correspondingly equal times. As shown in Fig. 7, modulated pulses, of the form shown in Fig. 1 with their front edges F recurring at equal time intervals, are fed as synchronizing pulses to a saw-tooth oscillator 3, the output of which passes to an amplitude limiter 4 as in Specification 582,324 to produce pulses of constant duration as shown in Fig. 2. After amplification at 5, the constant duration pulses are combined differentially at 6 with the original pulses to produce a train of shorter pulses shown in Fig. 3, the shortest pulse A of Fig. 1 being reduced to a desired minimum duration LO. Unnecessary expenditure of power during periods of low percentage modulation is thus avoided. An alternative method consists in combining the original modulated pulses with these same pulses delayed by a suitable interval, and utilizing the shortened pulses represented by the high-amplitude portions of the combination. The delay may be introduced by a network interposed in one of two parallel-connected paths (Fig. 8, not shown), or by a network connected in shunt to the main path and arranged to give a delayed reflected pulse (Fig. 9, not shown).