Patent GB-404140-A (GB)
Title: Improvements in wave signalling methods and apparatus
IPC: H04J3/04
Filed: 1933-01-09
Abstract: 404,140. Valve circuits for wireless reception; multiplex wireless signalling. RADIO RESEARCH LABORATORIES, Inc., 597, Madison Avenue, New York, U.S.A. Jan. 9, 1933, No. 765. Convention date, Oct. 25, 1932. [Class 40 (v).] The input-voltage plate-current characteristic of a tetrode or pentode valve is given an inverted V-shape (shown in Fig. 2) by applying the input across the control grid and an auxiliary grid, and connecting a resistance or impedance between the auxiliary grid and the cathode. The plate current Ip is reduced to zero by either reducing or increasing the grid voltage beyond given limits. The valve may be used as detector and separator of multiplex signals transmitted on a common carrier wave but with different ranges of amplitude and percentage modulation. As shown in Fig. 7, the valve is employed as an amplifier or detector of radio-frequency signals. The timed input circuit 53, fed from an aerial 50 and amplifier 51, is connected between the control grid 63 and screen-grid 64 of a tetrode valve T. The cathode 62 is connected to the screen-grid 64 through a resistance 68, battery 67, grid condenser 70 shunted by a resistance 71, and highfrequency choke 72. The plate circuit of the valve includes an output transformer, a hightension source, and the battery 67 and resistance 68. The static grid bias is adjusted by a tapping 69 to such a value that when a carrier of a desired amplitude is received, the modulation carries the working-point up and down a straight part of the V-shaped characteristic, preferably the rising part. A weaker or stronger carrier will not give an effective output Other valve circuits coupled to the amplifier 51 at the points 54, 56 may be adjusted to respond to different strengths of carrier wave, enabling three separate channels of communication to be maintained on a single carrier wave. Fig. 5 shows a transmitting circuit for this multiplex system. The carrier wave for three separate channels is generated at 20 and is amplified to different levels in passing to the channels a, b, c. Each channel is modulated by a separate signal generated at 21a, 21b, 21c, the modulation being deeper the weaker the carrier. Each channel is connected to a separate anode in a cathode-ray tube 23, the ray being traversed across the anodes, preferably in cyclic order, by the deflecting electrostatic effect of plates 28, 29 connected to a source 30 of supersonic frequency. The commutated wave is amplified and radiated by the aerial 32. In a modification, commutation is effected by rotating a toothed wheel across light beams carrying the respective signals. Those signals may comprise voice signals, and associated television and synchronizing signals; vocal music and accompanying instrumental music ; or any desired signal accompanied by a jamming or masking signal for securing secrecy. Although described for the reception of radio signals, the valve circuit of Fig. 7 may be employed for repeating signals of any frequency, and the elements 70-72 may be replaced by a pure resistance. The shape of the characteristic curve permits the valve to be used as an eliminator of static interference or other excessive voltage surges. The input to the valve may be applied through two transformers with their primary coils in parallel, and their secondary coils in series between the two grids. A grid leak and condenser may be connected between the cathode and the junction of the two coils, and static bias may be applied to both grids from a voltage-divider across the plate supply source.