GB600259A - Improvements in or relating to receiving circuits for time modulated electric pulses - Google Patents

Abstract

600,259. Pulse modulation. STANDARD TELEPHONES & CABLES, Ltd. Jan. 15, 1945, No. 1233. Convention date, May 24, 1943. [Class 40 (v)] In a receiver for time-modulated pulses, the pulses are applied to trigger a blocking oscillator which produces an impulse for each operating interval thereof and operates at a lower natural frequency than the recurrence frequency of the received pulses. Applied also to the oscillator are locally generated voltage pulses of duration at least as large as the maximum degree of modulation of the received pulses, to increase its susceptibility to actuation by the latter during the period during which they occur. In one embodiment, the blocking oscillator 20 with its associated oscillatory circuit L, C has a natural recurrence frequency considerably less than that of the incoming modulated pulses from the aerial 10 and coupling coil 19. It is rendered capable of being triggered by the signal pulses by the application to the grid of rectangular pulses from the multivibrator 14 generated at the appropriate recurrence frequency under the control of the synchronizer 16, fed from the output of valve 20, in parallel with the demodulator 18. The natural recurrence frequency of the blocking oscillator can be adjusted by the screen grid bias control 32. A differentiating circuit 76, 77 is included in the oscillator output circuit to produce narrow pulses for feeding to the demodulator and synchronizer. A demodulator circuit, similar to that described in Specification 600,291, comprises a valve 100, Fig. 3, biassed to cut-off by resistance 102 and having time-modulated signal pulses applied to one grid, another grid being connected to an oscillatory circuit 105 tuned to twice the pulse recurrence frequency and shock-excited by the pulse energy. The resulting amplitude modulated pulses appear across the anode load resistance 109. The multivibrator 14 is synchronized by the output of the oscillatory circuit 105. In a modification, Fig. 4, the oscillatory circuit is replaced by a known synchronizing sine wave generator 150 having a frequency which is a selected multiple of the mean recurrence frequency of the pulses applied to it and to the modulator valve 100. Specification 600,255 also is referred to.