GB559717A - Improvements in or relating to variable tuning systems for radio signal receiving apparatus and the like - Google Patents

Abstract

559,717. Inductances. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Aug. 28, 1942, No. 12117. Convention date, July 1, 1941. [Class 38 (ii)] [Also in Groups XL and XXXVI'] A unit particularly for tuning the aerial and oscillator circuits of a superheterodyne receiver comprises a variable pitch coil 5 on a former 25 mounted on a rubber bush 26, the coil being provided with an axially movable magnetic core 6. Supported by a rubber bush 31 on the former 25 is a conducting shell 16 which forms the fixed element of a condenser, the movable element of which is a conducting cylinder 17. Conjoint movement of elements 6 and 17 is provided by their connection to a bridge member 33 axially slidable on rods 34 by means of a cord 37 actuated by a knob 38. A dielectric coating 50 serves to insulate members 16 and 17 and to provide the desired capacity, while connection to member 16 is made by a lead 48 connected to a copper sleeve 47. A magnetic shield 52 is provided round the coil 5. A circuit is described in which condenser 16, 17 is used to tune the loop antenna circuit of a superheterodyne receiver, the inductance 5, 6, serving to tune the oscillator circuit. Tracking is effected by means of the variable pitch of winding 5 and by the adjustable connection 43 between the core 6 and actuating bridge 33. In a modification, Fig. 4 (not shown), the magnetic shield 52 and copper sleeve 47 are dispensed.with, while in a further modification, Fig. 5 (not shown) the fixed condenser element is constituted by a conducting coating on the outside of the magnetic shield.