GB334765A - - Google Patents

Abstract

334,765. Telefunken Ges. f³r Drahtlose Telegraphie. Nov. 2, 1928, [Convention date]. By varying capacity.-An electric oscillation generator comprises a bar of material, not necessarily having magnetic or piezo-electric properties, coupled to and controlling a thermionic valve which supplies energy at the determined frequency and is back-coupled through electrostatic means to maintain the bar in vibration. Fig. 1 shows a circuit employing a bar 1 of insulating material such as fused quartz. The bar at its centre forms the dielectric of a condenser 2 connected in series with a resistance 4 and a source of e.m.f. 3 and its ends pass loosely through metal rings 6, 7 which are connected respectively to the negative and positive ends of the battery 3, ring 7 being connected through an oscillatory circuit 8. Assuming the bar to be vibrating longitudinally at its natural frequency with a node at the centre, the material of the bar at the centre will be subjected to an oscillatory stress which will produce a corresponding variation of the capacity of the condenser 2. An oscillatory current will flow through the condenser producing an alternating potential on the grid of valve 5. The current which flows in the anode circuit will produce an oscillatory e.m.f. in the circuit 8 which will cause the potential between the rings 6, 7 to oscillate about the steady value of battery 3. The steady biasing voltage produces compression of the bar and the alternating component increases and decreases this compression, thus causing the bar to vibrate. Fig. 2 shows a modified circuit for use with a metal bar. Two plates 10, 11 are arranged facing one end of the bar 1 and form with the bar two condensers in series, so that when the bar vibrates the series capacity is varied and an alternating current flows round circuit 10 - - 13 giving an alternating potential on the grid of valve 5. Across the plates 10, 11, and 16 is imposed the steady potential of the battery 15, and the rod is subjected to tension by the electrostatic attraction, but this tension is increased and decreased by the alternating component of voltage induced in the oscillatory circuit 8 by the coil 9 and rod is thereby maintained in vibration. Valves in cascade may be used to obtain further amplification.