GB520254A - Improvements in or relating to oscillation generating circuits - Google Patents

Abstract

520,254. Valve generating, modulating, and relaying circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Oct. 17, 1938, No. 30067. Convention date, Oct. 16, 1937. [Class 40 (v)] An additional electrode is provided in a self excited oscillator valve which serves no function in the production of oscillations and has a biasing potential applied to it to maintain the amplitude of the oscillations constant, the biasing potential being produced from the oscillations in the tuned circuit. Fig. 1 shows an oscillator having the tank circuit 5 connected between the grid 3 and the anode with a bias derived from the grid leak 6 applied through a filter to the grid 10. A modulating source 14 may also be connected to the grid 10 and will not affect the controlling bias, the speed of control of which is determined by the time constant of impedances 7, 13. Instead of the valve'cathode being earthed the anode or the grid may be earthed, Figs. 2 and 3 (not shown), and a fixed bias source may be provided in series in the controlling circuit, Fig. 2a (not shown). A pentode may be used instead of a pentagrid type valve and the system used as a burglar alarm, Fig. 5, the antenna-ground capacity 21 and the consenser 22 forming a variable potentiometer across the tank circuit and controlling the energy fed to a remote carrier-operated relay. The controlling bias may be produced by amplifying the oscillations generated. Fig. 6 shows an amplifier 24 the output from which is applied to an attenuation network and to a rectifier 30 in the load circuit of which a resistance 31 is provided across which the controlling bias is taken. Modulation may be effected through condenser 13'. Fig. 7 shows an alarm comprising an oscillator 1 the bias of the grid 10 being controlled by the diode electrodes 36, 37. The anode supply is AC and the valves are so arranged that in one half of the cycle the valve 1 oscillates and determines the bias on the grid 37 which, in the next half cycle, controls the operation of relay 56. In a modification a three grid oscillator valve is used, Fig. 8 (not shown). Modulation by a condenser microphone may be effected by arranging the microphone as part of a potentiometer across the tank circuit and feeding the modulated direct current voltage to an output amplifier, Fig. 9 (not shown). Specification 454,059 is referred to. Reference has been directed by the Comptroller to Specification 498,807.