Patent GB-188678-A (GB)
Title: Improvements in the generation and modulation of continuous waves for wireless telegraphy and telephony
IPC: H04B1/04
Filed: 1921-05-09
Abstract: 188,678. Blondel, A., and Touly, M. May 9, 1921. Thermionic oscillation generators and modulating systems.-Apparatus for generating oscillations comprises two thermionic valves, or valve groups, connected in cascade, the grid and plate circuits of the power valve being coupled so that this valve is on the verge of oscillation, whilst a second back coupling between the power valve and the relay valve sets the whole system in oscillation. Keying or modulation for telegraphy and telephony is effected in the relay or low-power valve. In the circuit arrangement shown in Fig. 1, the main valve A' has its plate circuit energized by the combined batteries B1, B2 and directcoupled to the aerial a. A coil Lm in the grid circuit of the valve A2 is coupled to the aerial inductance La and so puts this valve on the verge of oscillation. A coil L<1>m also coupled to the coil La is connected in the grid circuit of the auxiliary valve A1, which has its plate circuit energized by the battery B, through an impedance Z. The plate of the auxiliary valve is connected to the grid G2 of the main valve through a condenser y2. The oscillatory current derived from the coupling L'm, La is fed to the grid G<1> and the variations of plate current through an impedance Z affect the potential of the grid G2 in the correct phase to sustain oscillation. Signals may be produced by a microphone or key m connected across part of a coil L in the circuit of the grid G1. In a modification shown in Fig. 2, two auxiliary valves A1, A<1>1 are coupled in cascade, and the plate circuit of the valve A', is coupled to the grid circuit of the main valve A2. The main valve has a condenser Co connected between the plate inductance La and the grid G2, but the reaction afforded by this condenser is not sufficient in itself to cause the valve A2 to oscillate, but merely reduces the damping. The condenser Co for reducing damping may be connected to the grid of the valve A1, or it may be replaced by an inductive coupling to the grid circuit of the valve A<1>1. The effective back coupling for the production of oscillations is, however, by the coil Lm connected in the grid circuit of the first auxiliary valve A1. The coupling between the valves A1, A<1>1 comprises a tuned circuit L, C, gamma2, and the microphone M may be connected through a condenser Cc across this circuit.. Any number of auxiliary valves may be used in cascade or in parallel and with any suitable inter-coupling. Fig. 3 shows a modulating arrangement in which the grids of two valves A<1>1, A<1>2 are differentially excited by the microphone M acting through the transformer tm, while their plates are given like potentials by the coil L<1>m coupled to the aerial inductance La. The two plate circuits are coupled differentially to the grid circuit of the valve A1, so that when the microphone is inactive no effect is produced on the valve A1, and when the microphone is operative modulated oscillations pass to this valve. The valve A, is coupled to the power valve A2 in the manner described with reference to Fig. 1, and a similar back coupling Lm for reducing damping is provided for the power valve. The plate and filament circuits of the valves may be fed with alternating current through transformers. Direct-current dynamos may also be used having several armatures and collectors, or with a single armature and collector, and several brushes for dividing the total electromotive force into suitable fractions for the different valves.