Patent GB-596638-A (GB)
Title: Improvements in or relating to the generation of electric pulses
IPC: C11D3/39
Filed: 1944-03-30
Abstract: 596,638. Pulse generating and modulation circuits. STANDARD TELEPHONES & CABLES, Ltd., CHATTERJEA, P. K., AMBROSE, D. M., and BENEY, J. K. March 30, 1944, No. 5940. [Class 40 (v)] In a pulse generator, a saw-tooth generator controls a device alternating between two conditions of stability, means being provided for varying the period during which the device remains in one condition and the control exerted by the fly-back is increased to ensure the return of the device to the first condition. By applying a signal wave to the device, the output pulses may be modulated. Pulse forming. A gas-filled valve V1, Fig. 1, generating saw-tooth waves, feeds a gas-filled valve V2, over coupling condenser K1 and attenuating potentiometer P3, causing it to fire when the saw-tooth voltage exceeds the cut-off bias provided by battery S2 and potentiometer P2, to form the leading edge of the pulse at the anode of valve V2 and output terminal 2. The valve V2 is extinguished to form the trailing edge of the pulse, by a negative pulse formed by differentiating the saw-tooth voltage over condenser C2 and resistance G. Alternatively, a tuned circuit may be included between the cathode of valve V1 and earth, the damped oscillations being fed over a coupling condenser to the grid of valve V2. The controls of resistance R1 and condenser C1 may be calibrated in recurrence frequency, the setting of potentiometer P1 being used for trimming purposes. Where a wide range of frequencies is contemplated, condensers C1, C2 may be varied in steps, the resistance R1 being continuously variable for fine adjustment. The potentiometer P2 may be calibrated in pulse width and a milliammeter inserted in the anode of valve V2 to act as a monitor. In a modification, Fig. 3 (not shown), a double grid gas-filled valve is employed, the saw-tooth signal being applied to one grid and the extinguishing voltage derived from the saw tooth applied to the other. The pulse may be inverted by feeding the output from terminal 2 to the grid of a hard triode, Fig. 6 (not shown), the cathodeanode circuit replacing resistance R3, the inverted pulses being obtained from a load in the anode lead. Secondary pulse trains. The saw-tooth and pulse waveforms from the circuit of Fig. 1 are added in potentiometer P11, Fig. 9, and fed to valve V8 operating in a similar manner to valve V2. By adjusting potentiometer P4, the sawtooth and pulse waveforms may be made of equal amplitude so that a new saw-tooth voltage appears at the grid of valve V8, the corresponding pulse at the anode being retarded in time by the width of the primary pulse. The process is repeated in valve V9, to form a third series of pulses and this may be repeated indefinitely. In a modification, Fig. 10 (not shown), the primary saw-tooth is used throughout, but both primary and secondary pulses are added to the valve corresponding to V9 to form the third pulse. To avoid undue complication in the grid circuits of subsequent valves, a new saw-tooth voltage may be formed after every second or third valve in the chain. Marking pulses corresponding to the leading and trailing edges may be produced by feeding them through a differentiating circuit. Pulse modulation. The pulse generator at terminal 2, Fig. 1, may be frequency modulated by applying a signal to terminal 14 and duration modulated by a signal at terminal 13, the signals varying the bias of valves V1 and V2 respectively. When using the circuit of Fig. 9, signal voltages applied over terminal 13 timephase modulate the output pulses at terminal 15, while the signal applied to the grid of valve V8 duration modulates the pulses. By applying a signal at terminal 13 and a voltage of twice the amplitude and opposite sign to the grid of valve V8, a symmetrical duration modulation may be obtained. Where a pulse of considerable power is required, the output pulse may be fed to an amplifier, Fig. 7 (not shown), comprising an inverting amplifier feeding a cathode follower delivering the power pulses. Specifications 593,461 and 596,702 are referred to.