177,269. Preston, L. G., Airey, H. Morris-, and Shearing, G. Dec. 24, 1920. Thermionic oscillation generators; keying systems and apparatus.-In a wireless transmitter comprising several valve generators connected in parallel, there is a tendency for the oscillations produced by a particular valve to be partially shunted through the remaining valves, instead of passing to the aerial. This is obviated by making each valve active in turn as an oscillation generator, and rendering it non-conductive during its inactive periods by giving its grid a high negative potential. Fig. 1 shows an arrangement in which three valves V1, V2, V, are energized by a threephase source, their plates being connected to the aerial through condensers C1, C2, C, and their filaments earthed. The grid coupling coil D, shunted by a condenser K, is connected at one end to the earthed filaments, and at its other end to the respective grids G1, G2, G3 through leak resistances R1, R2, R3 shunted by condensers K1, K2, K3. Across each leak resistance Is connected a two-electrode valve W1, W, in series with a commutating arrangement L which intermittentlv connects in a direct-current source O. The commutator L is driven by a synchronous motor N energized by the polyphase supply and makes one revolution per cycle. Two-thirds of its rim is conductive and one-third insulating. The conductive portion is connected to the negative terminal of a direct-current generator O driven by the motor N. The rim is engaged by three brushes a', b<1>, c' spaced 120‹ apart and connected to the filaments of the three valves W1, W2, W3. The positive terminal of the generator 0 is connected to a point between the grid coupling coil D and the resistances R1, R2, R3. The voltage of the generator O is thus connected in series with the two-electrode valves W1, W2 whenever the corresponding brushes a1, b1 lie on the conductive part of the commutator L, whilst the circuit of the valve W3 is open on account of its brush c<1> resting on an insulated portion of the commutator. When the generator O is in circuit the grids G1, G2 of the corresponding generator valves Y1, V2 become highly negative and the valves become non-conductive, while the grid G<3> of the other valve is at a suitable potential for generating oscillations, which pass to the aerial and are not shunted through the valves V1, V2. 'With the rotation of the commutator each valve generates in turn. During the " spaces " between the signals, all three valves are rendered inactive simultaneously by closing switches d, e, f which put the generator O in circuit independently of the commutator L. The switches d, e, f are controlled by the signal key, being closed for spaces and open for signals. Fig. 3 shows a modification in which the auxiliary valves X1, X2, X3 are of the three-electrode type and are connected in series with the grid leak resistances R1, R2, R3 of the main valves. The grids of the auxiliary valves are given a negative potential by batteries D1, D2, D3 shunted by condensers. The batteries are connected at one end to a continuous ring e' of the commutator and at their other ends to brushes, a<1>, b<1> c<1 >bearing on rings which are insulated for two-thirds of their rims, and conductive for the other third. The batteries D1, D2, D3 are thus short-circuited in turn, the effect of the short-circuiting being to render the corresponding main valve operative. The short-circuits include contacts d, e, f controlled by the signal key. The main valves may be energized by direct current from the same or from different sources. In a modification of the arrangement shown in Fig. 1, the auxiliary valves W1, W2, W3 are omitted, and an alternating current is rectified by a two-electrode valve and is utilized to charge a condenser. The commutator puts this condenser in turn across the leak resistances with its negatively-charged plate connected to the grid, thus rendering the corresponding valve inactive.