GB574407A - Improvements in or relating to antenna input circuits for radio receivers - Google Patents

Abstract

574,407. Aerial coupling arrangements. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Jan. 28, 1944, No. 1591. Convention date, Jan. 28, 1943. [Class 40 (v)] An antenna input circuit for a radio receiver comprises a high-frequency auto-transformer, a ferro-magnetic core movable relatively thereto, a capacity in shunt with the secondary of the auto-transformer and forming therewith a secondary resonant circuit tunable by movement of said core throughout a range of frequencies,-and a loop antenna in shunt across the primary of the auto transformer and forming therewith a primary resonant circuit which is tuned by said core to a frequency higher than the frequency to which said secondary circuit is tuned by said core. As shown in Fig. 1, a loop antenna 1 is connected to a tapping on a coil 2 which, together with condenser 3 forms the input circuit of a valve 4, and is tunable by movement of a ferromagnetic core 5. Movement of core 5 varies the inductance of the two portions of coil 2 and also the mutual inductance between them so as to give a fairly uniform energy transfer over the frequency range. The tapping is adjusted so as to include from 25 per cent to 35 per cent of the coil between the tapping and ground. The resonant frequency of the circuit comprising the loop and the part of the coil is above the highest frequency of the tunable range of circuit 2, 3.