GB488254A - Improvements in or relating to electrical wave filters - Google Patents

Abstract

488,254. Impedance networks. CORK, E. C., and PAWSEY, J. L. Dec. 23, 1936, No. 35295. [Class 40 (iii)] Two circuits tuned to the same frequency are connected by a transmission line, an odd number of quarter-wavelengths long at the frequency to which the circuits are tuned, so that one circuit presents an impedance inverse to the other, and a constant input impedance is obtained. The networks are used in band stop or separator filters, and frequencies in the pass ranges are transferred with equal time delay. In Fig. 1, the circuits 1, 2 are tuned to the sound-carrier of a television system and are spaced a quarter of the sound-carrier wavelength apart ; the filter suppresses the sound carrier ; the equivalent circuit comprises a shunt connected series tuned circuit and a series connected parallel tuned circuit, Fig. 2 (not shown). The shunt connected series tuned circuits of Fig. 1, may be replaced by series connected parallel tuned circuits, Fig. 3 (not shown), and the quarter-wavelength line may be tapped onto the parallel tuned circuits, Fig. 6 (not shown). The network of Fig. 1 may have series connected parallel tuned circuits associated with each of the circuits 1, 2, Fig. 4 (not shown). An inverse network for accepting the sound-carrier comprises shunt connected parallel tuned circuits 4, 5, Fig. 5, associated with series connected series tuned circuits 1, 2 separated by a quarterwavelength line. As applied to a separator, one of the tuned circuits of Fig. 1, is connected in shunt, Fig. 7, so that circuit 1 accepts the sound-carrier while circuit 2 and the quarter wavelength line accepts the vision-carrier ; the equivalent circuit comprises a series tuned circuit in parallel with a parallel tuned circuit, Fig. 8 (not shown). The circuits 1, 2 of Fig. 7 may be replaced by inversely connected parallel tuned circuits, Fig. 9 (not shown) ; the circuit 1, Fig. 7, may be replaced by a shunt connected parallel tuned circuit in conjunction with a quarter-wavelength line, Fig. 10 (not shown). When the network is used to suppress the sound carrier, by coupling the sound-receiver to the first tuned circuit, the sound-carrier may be obtained, Fig. 11 (not shown). The tuned circuits may be replaced by long lines Figs. 15, 16 (not shown). U.S.A. Specification 1,933,669 is referred to.