GB583511A - Improvements in or relating to arrangements for producing electric time modulated impulses - Google Patents

Abstract

583,511. Pulse modulation. STANDARD TELEPHONES & CABLES, Ltd., and AMBROSE, D..M. Sept. 26, 1941, No. 12503. [Class 40 (v)] Time modulated pairs of pulses such as F, M, Fig. 2, are converted into single pulses of variable duration. The pulses F of the series occur at fixed time intervals and the intervals between F and the next variable pulse M represent corresponding instantaneous signal wave amplitudes, or the fired pulses F are transmitted pulses of an obstacle detection system, M being the reflected pulses. In the arrangement shown in Fig. 1, the pulses are applied to the grid circuits of valve V1 and of a discharge tube V2 forming part of a conventional saw-tooth wave generator. The pulses are differentiated by the condenser 11 and resistance in the input circuit of V2 so that short positive and negative impulses are derived from each pulse, the positive impulses derived from the fixed pulses being used to synchronize the generator. The saw-toothed output is applied to pentode V3 biased so that is accepts only the wave tips which are applied as negative pulses to valve V4 of a reciprocally coupled pair having two conditions of stability. To ensure proper operation by the fixed pulses which are applied to both valves, the fixed pulses produced by the saw-tooth oscillator may be slightly longer than the fixed pulses in the input train. The variably timed pulses are reversed in polarity by valve V1 and applied as negative pulses to the grid of the other valve of the pair, the output from which therefore, comprises pulses of variable duration. In a modification, Fig. 3 (not shown), a condenser charged.by incoming pulses over a diode controls the anode potential i of a gas discharge tube. A single pulse is just insufficient to raise the potential to ionizing value but the arrival of a second pulse quickly causes discharge. The substantially square topped variable duration pulses in the output of the discharge tube are shaped by a valve which accepts only the central portion of the amplitude range. Pulses of undesired opposite polarity in the input may be removed by a second reversely connected diode.