GB957202A - Improvements in or relating to electric signal receivers - Google Patents

Abstract

957,202. Inductances. MULTITONE ELECTRIC CO. Ltd. Sept. 22, 1961 [Sept. 13, 1960], No. 31550/60. Heading H1T. [Also in Divisions H3 and H4] A paging system receiver for speech modulated low-frequency ratio waves radiated within a confined area from surrounding wires comprises a pick-up coil L1 wound on an axially movable ferrite rod with or without a bobbin and/or paper interleaving with plural tappings so that the windings between adjacent tappings and between each terminal and adjacent tappings are all of the same axial length and are uniformly distributed over the coil length; the coil being tunable by axial movement of the core at one frequency and thereafter being correctly tuned at other frequencies selected by a tapping switch connecting a damping resistance and series capacitors C1 C2 across the coil. The junction of the capacitors is connected to the base of transistor T1 whose collector circuit incorporates tuning coil L2 wound on a ferromagnetic core with a gap bridged by a tuning slug and having corresponging switchable taps shunted by tuning capacitor C3 and damping resistor R12. Capacitor C4 couples the output to the base of rectifier/amplifier transistor T2 whose collector circuit includes earpiece P. Potentiometer R1 regulates the bias current of transistor T1 through resistor R2 to set the weak signal gain and AVC level, while signals on the base of T2 develops a positive mean potential fed back over resistor R3 to control the gain of T1. In a modification (Fig. 2, not shown), the output of L2 is applied to the base of a further amplifying transistor coupled over an aperiodic transformer to a rectifier/amplifier transistor feeding an earpiece, and deriving AVC bias applied to the amplifying transistors as before.