Patent GB-548948-A (GB)
Title: Improvements relating to electronic reactance devices
IPC: H03J7/04
Filed: 1941-04-28
Abstract: 548,948. Automatic control systems. STERLING, Sir L. April 28, 1941, No. 5457. Convention date, April 27, 1940. [Class 38 (iv)] [Also in Groups XL and XXXVI] An electron discharge tube connected across an oscillatory circuit for varying its tuning comprises a cathode, an accelerating electrode, and a decelerating output electrode adjacent to which a space charge accumulates, means being provided for controlling said space charge by a controlling voltage. As shown in Fig. 2 the oscillatory circuit 14, 15 is associated with a back-coupled generator valve 10, and is connected across the plate 24 and cathode of the control valve 20. The outer grid is held positive, but the plate is earthed through a choke 25. Control voltage for frequency modulation or other purpose is applied through a transformer 35 to the inner grid, which also receives oscillatory voltage from the grid of the valve 10. The varying space charge at a point between the outer grid and the plate induces electrostatically on the plate an oscillatory voltage displaced in phase by 90‹, and thus provides an adjustable reactance across the tuned circuit 14, 15. A further control tube may be associated with the generator valve 10 in the same way as the control tube 20, and its reactance may be regulated by a control voltage derived from a frequency discriminator fed by the generated oscillations (Fig. 3 not shown). This control may be arranged to operate slowly so as to counteract frequency drift, or it may operate rapidly to produce a negative feed-back effect and so reducing distortion. In Fig. 4 the reactance control tube 20 has its plate 24 connected to the grid of a phase-reversing amplifier 62 which is connected across the tuned circuit 14, 15. The plate circuit 61 of the tube 20 is tuned, and the control voltage is applied to an extra innermost grid. The oscillator valve 10 and control valve 20 may be in a single envelope (Fig. 5 not shown), and may be used as the local oscillator in a superheterodyne receiver with automatic tuning correction (Fig. 6 not shown). In Fig. 4 pentode tubes may be used both in the control stage 20 and in the amplifier stage 62 (Fig. 7 not shown). Control of the reactance of the tube 20 may be effected by variation of its negative plate voltage (Fig. 9 not shown). The oscillator 10 may be crystalcontrolled, and the quadrature potentials induced on the plate of the reactance valve 20 may be amplified by any suitable amplifier before being impressed across the tuned circuit 14, 15 of the oscillator (Figs. 10 and 11 not shown). In Fig. 12 (not shown) the valve 115 sustains oscillations in the anode circuit 14, 15 by virtue of the back coupling condenser 123 inserted between the anode 120 and the control grid 117, the latter being connected to the cathode through a crystal 110. The quadrature voltages induced on the decelerating grid 118 are amplified by a twostage resistance-coupled amplifier 125, 126 and are fed into the anode circuit of the valve 115. Frequency control is effected by varying the gain of the valves 125, 126. The kind of reactanceintroduced, whether capacitive or inductive, is determined by the number of stages of the amplifier 125, 126. The feed-back from the output of valve 126 may be to the control grid of the valve 115 (Fig. 13 not shown). When the main oscillatory circuit is energized by an oscillator of fixed frequency, the modulating potential causes a phase shift in the oscillatory current as in phase modulation.