GB581613A - Improvements in or relating to oscillation generators - Google Patents

Abstract

581,613. Pulse generating circuits. STANDARD TELEPHONES & CABLES, Ltd., and EARP, C. W. Sept. 15, 1944, No. 17730. [Class 40 (v)] A pulse generator comprises a pentode valve with regenerative condenser coupling between the anode and the control grid and with a tuned circuit in the cathode lead to synchronise the output pulses which are taken from the screen grid. In Fig. 1, an initial flow of anode current through pentode 1, produces a fall in anode voltage which reacts on the control grid through condenser 12. The fall in grid voltage reduces the screen current, and as this constitutes most of the cathode current, the cathode voltage falls by reason of bias resistance 6. As cathode voltage falls below fixed suppressor grid voltage anode current increases, the corresponding fall in anode voltage being transferred to the control grid through condenser 12 until valve current is completely cut off. Grid voltage is restored through leak resistance 13 and rises until the cathode voltage again exceeds the suppressor grid voltage, when cycle is repeated. Pulses produced when the space current is cut off " ring " resonant circuit 7, 8 so that an alternating voltage is superimposed on the cathode voltage and the frequency of the pulses is determined exactly by the ringing frequency. A diode 14, prevents control grid voltage from exceeding the suppressor grid voltage. In synchronising this circuit by means of a pulse train, the synchronising pulses may be applied at 17 or, to eliminate the effect of interference, through a gating circuit. Fig. 4 shows a gating pentode 21, biassed to be normally blocked and unblocked by a pulse from the screen of the oscillator pentode, suitably delayed to synchronise with the arrival of succeeding pulses at the grid of pentode 21. The amplified pulse is applied through condenser 34 to the anode of the oscillator pentode for synchronisation purposes. In a further modification, an amplified train of pulses from the gating pentode 21 is applied to inductance 7 of the ringing circuit in the oscillator cathode circuit by means of an inductively coupled winding (Fig. 5, not shown).