GB277390A - A system of modulating high frequency currents of thermionic tube transmitters for wireless purposes - Google Patents

Abstract

277,390. Mandelstam, L., and Papalexi, N. March 10, 1926. Thermionic modulating systems and apparatus; thermionic generators.-Modulation of the high frequency currents of a thermionic valve, which may be a drive oscillator or an amplifying valve, is effected by a variation in the high frequency voltage acting on the grid, which voltage is produced in an impedance inserted in the grid-filament path. The grid current flows through the impedance, which is so proportioned that the current flowing is mainly determined by the gridanode capacity of the valve. Fig. 2 shows an arrangement in which the grid circuit impedance 3 is constant and the current flowing is varied by variation of the grid-anode impedance. The grid-anode capacity is shunted by a condenser 10 and an inductance 11 and modulation is effected by varying either of these. Alternatively a constant grid current may be employed and the impedance 3 may be varied, e.g. as shown in Fig. 4, in which two auxiliary magnetized chokes are employed, the windings 31, 32 of which form the high frequency impedance, which is variable by means of the windings 141, 142 fed from a microphone circuit 13. In a modification, the impedanca 3 is shunted by the anode-cathode path of an auxiliary valve, the impedance of which is varied in accordance with the low-frequency input. Formulµ and a numerical example are given in the Specification showing how the value of the impedance 3 is determined.