Improvements in band-spread tuning circuits for radio receivers

摘要

542,611. Radio receiving apparatus. MULLARD RADIO VALVE CO., Ltd., CAPLIN, F., and PAYNE, C. E. July 9, 1940, Nos. 11451/40 and 2231/41. [Class 40 (v)] [Also in Group XXXVI] Band-spread tuning is effected by a variable inductance L, Fig. 3, which is not part of the tuning circuit proper but is connected in parallel with an inductance L 3 forming part or all of the tuning coil or having a mutual inductance coupling with the tuning coil L 1 , the main tuning being performed by the variable condenser C. A condenser C 1 may be inserted in the connection between the inductances L, L 3 to render the band-spread tuning more uniform. When the receiver is provided with two main tuning coils L 1 , L 2 , Fig. 5 adapted to be connected alternatively by a switch S 1 to a condenser C for two wave bands, a single band-spread variable inductance L may be provided and connected alternatively to the tuning circuits by a switch S 2 mechanically coupled with the switch S 1 . The inductance L may be made variable by means of an adjustable core 11, Fig. 6, attached to a stem 12 influenced by a spring 15 and controlled by a helical cam 17 set by the rotation of a knob 19. In a modification, a spiral edge-cam rotating on a transverse axis is used. Specification 536,412 is referred to.