Patent GB-436482-A (GB)
Title: Improvements in or relating to modulated carrier wave receivers
IPC: H03G5/26
Filed: 1934-10-16
Abstract: 436,482. Valve circuits for wireless reception; filter circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London.- (Assignees of Braden, R. A.; 509, Cedar Avenue, Collingswood, New Jersey, U.S.A.) Oct. 16, 1934, No. 29639. Convention date, Oct. 16, 1933. [Classes 40 (iii) and 40 (v)] The selectivity of a wireless receiver is varied inversely as the received signal strength by rectifying the received signal and employing the D.C. voltage so obtained (1) to vary in opposite directions the tuning or (2) to vary the degree of coupling, of two or more frequency-selective circuits. The D.C. voltage may be applied to the grids of valves the plate currents of which vary the degree of saturation of the iron cores of coils in the tuned circuits. As shown in Fig. 1, the tuned circuits I, II separated by a valve amplifier 1, are followed by a further amplifier 2 and detector 3. The tuned circuits include iron-cored coils L<1> L<11> the saturation of which is varied by the plate current of valves V1, V2. The grid voltage of these valves is determined by tappings on a resistance R in the detector plate circuit, and the conductance of the valves is varied in opposite sense when the rectified carrier current through the resistance R varies. The circuits I, II are thus put out of tune in opposite directions as the signal strength increases, giving a broad resonance and greater fidelity for powerful transmissions, and greater selectivity for weak transmissions. Both the primary and the secondary circuits of the couplings M1, M2 may be tuned, and each may include an iron-cored coil associated with a valve V1, V2 (Figs. 2 and 3, not shown). In Fig. 5, the resonance curve is broadened when strong signals are received by varying the coupling between the tuned circuits 20, 21. The coupling-coils are wound on an iron core which also has a saturating winding 26 traversed by the plate current of a valve V<1>2. The grid voltage of this valve is determined by a tapping on a resistance 56 arranged in series with a diode rectifier fed from the tuned circuit 21 and forming part of a diode-triode valve 55. In addition to varying the coupling, the control tends to alter the tuning of the circuits 20, 21, and this is neutralized by ironcored coils L1, L<11> associated with coils 61, 62 in the plate circuit of a valve VI or a pair of valves. The grid voltage of this valve is taken from a resistance R2 in the plate circuit of the triode section of the valve 55, and the grid of the latter valve receives variable rectified voltage from the resistance 56, speech voltages being shunted by the filter 64, FC. In a modification, Fig. 6 (not shown), a single pentode valve replaces the two valves VI, V<1>2. The plate circuit of the pentode receives its voltage from a resistance in the output circuit of the triode section of the valve 55, and the pentode plate current traverses the coil 26. The circuit of the middle grid includes a battery and the coils 61, 62 ; and the other two grids are earthed. The system may be applied to carrier-frequency amplifiers or to intermediate frequency amplifiers of superheterodyne receivers. Specification 409,193 is referred to.