GB603196A - Improvements in or relating to thermionic valve pulse generating and modulating circuits - Google Patents

Abstract

603,196. Pulse modulation. McDERMOTT, T, J., and COOP, E. Nov. 13, 1945, No. 30386. [Classes 40 (v) and 40 (vi)] Duration modulated pulses are produced by arranging a condenser to discharge through a constant-current device to produce a saw-tooth waveform, a valve being provided to maintain the condenser charged when conducting, the modulating voltage determining the time after commencement of discharge at which the valve becomes conducting. In the embodiment described, the condenser C1 is charged through valve V2 and discharged by constant-current valve V1, when V2 is non-conducting. A negative-going trigger pulse at pulse recurrence frequency is applied to the suppressor grid of V2 which is rendered non-conducting thereby. It is cross-connected with valve V3 so that a rise in anode voltage of V2 produces a fall in the anode voltage of V3 which is applied to the control grid of V2 to maintain the latter non- conducting. The condenser C1 now discharges through V1 until the cathode of V2 reaches the control grid potential. This point of time is determined by the modulating voltage applied to the control grid of V3. Valve V2 now rapidly becomes fully conducting to re-charge condenser C1 and V3 reverts to its non-conducting state. Rectangular duration-modulated positive-going pulses are derived from the screen grid of valve V2. These may be differentiated and the negative trailing edge derived pulses segregated as phase-modulated pulses. The modulating signal may consist of interlaced amplitude-modulated channel pulses. of a multiplex, system, such as described in Specification 584,729, in which case the triggering frequency applied to the suppressor grid of V2 is the product of the channel pulse recurrence frequency and the number of channels.