GB571858A - Improvements in or relating to variable inductances - Google Patents

Abstract

571,858. Wireless receiving apparatus. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Oct. 25, 1943, Nos. 17504 and 17505. Convention dates, Oct. 24, 1942 and Nov. 21, 1942. [Class 40 (v)] [Also in Group XXXV] A variable inductance in a resonant circuit comprises an inductance coil and a main magnetic core adjustable relatively to the coil for providing coarse tuning of the circuit, and an auxiliary core adjustable relatively to the coil to provide fine tuning of the circuit. Fig. 2 shows one form of multiple core inductance suitable for use in band-spread tuning of a wireless receiver. Two insulating formers 11, 12 are mounted close together in a shield can 13. A coil L1 is mounted on the former 11 and has its inductance variable by means of a main core K1 of dust iron. An auxiliary core K2 slidable in former 12 serves to provide a small change of inductance for the complete range of movement of the auxiliary core. The shield can 13 enhances the effect by constraining the flux about the coil L1. For band-spread tuning, the main core K1 is adjustable in steps to positions corresponding to the centre frequencies of the several short-wave bands, and band-spreading throughout the selected waveband is effected by movement of the auxiliary core K2. In a modified construction, Fig. 5, the former 12 may also have a few turns L2 in series with coil L1 and in aiding phase. In this case the interaction of the two coils and cores gives a more satisfactory band-spread characteristic, which can also be improved by tilting the formers relativeto one another, by the provision of dust iron washers on the end of the coils, or by the provision of a dust iron shell between the shield can and the coils. Fig. 4 shows a number of units of the form shown in Fig. 2, used for bandspread tuning in a superheterodyne receiver comprising an aerial A, high-frequency stage 6, and detector-oscillator 8. The RF circuits 1<1> and the oscillator circuit 7 are all tuned by inductances each having a main core K 1 and an auxiliary core K2. The wavebands are selected by moving cores K1 in unison to positions corresponding to the centres of the bands, and band-spread tuning is effected by moving auxiliary cores K2 in unison. In a modified circuit, Fig. 7 (not shown), band-spreading is effected solely by tuning the oscillator circuit by a unit as shown in Fig. 5. In this case, the radio-frequency circuits have band pass characteristics, and are tuned for wave-band selection by the step-by-step movement of a single core. Specifications 571.787 and 571,836 are referred to.