GB454503A - Improvements in or relating to electrical filters - Google Patents

Abstract

454,503. Impedance networks. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London, and RUST, N. M., 109, London Road, Chelmsford. March 29, 1935, No. 9889. [Class 40 (iii)] A band-pass filter for use as an intervalve coupling comprises two tuned circuits L1, A, and L2B, Fig. 3 coupled by an impedance ZC comprising a plurality of parallel tuned circuits. When ZC consists of an even number of circuits, half are tuned above and half are tuned below the mean frequency of the band passed; while when ZC comprises an odd number of circuits, one is tuned to the mean frequency and the remainder are tuned, one half below and one half above the mean frequency. The condensers A, B may be split, and ZC connected between their junction points, Fig. 4. The impedance ZC may be connected between tappings on the inductances L1, L2, Fig. 5. A number of series tuned circuits may be connected between the junction of condensers A, B, Fig. 3 and the junction of inductances L1, L2, Fig. 1 (not shown), or may replace condensers 2C1, 2C2, Fig. 4. Such series tuned circuits may be introduced at YM, Fig. 7, and more complex circuits comprising coupling impedances ZC and YM are developed, Figs. 9, 10 (not shown). A switch may be incorporated to short-circuit certain of the parallel tuned circuits in ZC and so vary the selectivity of the filter, Fig. 11 (not shown).