GB506517A - Improvements in or relating to electric wave filters - Google Patents

Abstract

506,517. Impedance networks. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Nov. 29, 1937, No. 32912. Convention date, Nov. 28, 1936. [Class 40 (iii)] A relatively wide frequency band and an adjacent relatively narrow frequency band are separated by applying both filter to a band-pass filter including a mid-section shunt series-tuned arm 13, 14 resonant at the mid-frequency of the narrow band. The band-pass filter passes the wider frequency band, and the narrow frequency band is obtained from the shunt arm. The invention is particularly applicable to separating adjacent sound and vision modulated carriers. The filter is preferably of the T-network type and comprises tuned circuits 11, 20; 12, 21 coupled by the resonant arm 13, 14. A resistance 15 may be used to allow the shunt arm 13, 14 to introduce a high degree of attenuation at its resonant frequency as described in U.S.A. Specification 2,002,216. The capacities 20, 21, 14 may be the capacities between electrodes of valves, Fig. 2 (not shown), the circuits being tuned by variation of the inductances. The filter preferably has an M-derived section. British Specification 195,782, [Class 40 (iii)], is referred to.