GB484701A - Improvements in or relating to frequency controlling electrical circuits - Google Patents

Abstract

484,701. Valve circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Oct. 5, 1936, No. 26972. Convention date, Oct. 3, 1935. [Class 40 (v)] The tuned input circuit of a thermionic valve is varied in resonant frequency by means of a reflected impedance derived from a frequency control valve, the mutual conductance of which determines the magnitude of the impedance. In the schematic arrangement shown in Fig. 1, the input circuit of valve Tl has a composite reactance Z1, and the output circuit a reactance Z2, connected to the grid circuit of a frequency control valve T2 the anode of which is connected to the input of T1 over a feed-back condenser C3. The Specification discusses many forms which the reactance Z2 may have, and the resultant corresponding form of the reactances Z0 reflected across the input reactance Z1. Examples cited include Z2 as a capacity, Z0 then being a negative inductance and vice versa ; if Z2 is a negative mutual inductance, Z0 is a positive capacity. Complex networks may similarly be dealt with. Fig. 2 shows a cascade pair of screen grid amplifiers 1, 2, each with a frequency control valve 3, 4, the grid bias of which may be separately or conjointly varied to vary the tuning of the respective input circuits 5, 6. The impedance Z2 shown in Fig. 1 is here constituted by the negative mutual inductances M, M1, and ZO the reflected reactance across the input circuits 5, 6, is thus a positive capacity varying with mutual conductance of valves 3 or 4. Fig. 5 shows the application of the invention to varying the tuning circuit 54 of an electron-coupled oscillator 50. The supply choke 51 is assumed to be of negligibly high impedance, the reactance Z2 being constituted by condenser 34. The reactance reflected across 54 will thus be a negative inductance and the resonant frequency of 54 will be reduced as the gain of the control valve 52 is increased by reducing its,grid bias. The anode of 52 is coupled to the outer grid of 50 by the condenser 58. The invention may be applied to tuning over a wide frequency range, tone control, or to give automatic fine adjustment of tuning in manually or remote-controlled receivers. By reflecting back negative capacity, positive capacities may be neutralized by using the invention, in a wide band amplifier such as for television work, Fig. 3 (not shown). Specification 474,682 is referred to.