Wave filter

Abstract

Abstract 534,603. Impedance networks; transformers. STANDARD TELEPHONES & CABLES, Ltd. March 29, 1940, No. 5685. Convention date, June 2, 1939. [Class 40 (iii)] [Also in Group XXXV] In a filter of the balanced type comprising two or more sections 5, 6, Fig. 1, in tandem, the capacity unbalance is reduced by the connection of one or more condensers in series or diagonal between the input and output terminals. The stray capacities may be represented by a lattice network, Fig. 2, which may be so balanced that an E.M.F. applied across the input terminals will produce no output current if the product of the series capacities is made equal to the product of the diagonal capacities. This is done by the addition of a single condenser CA, CB or CC, Fig. 1, of suitable value. To balance for longitudinal currents, however, it is necessary either to make all the capacities of the lattice equal, in which case all three condensers CA, CB, CC are required, or to make the capacities such that the unbalanced voltage to ground at the input end is equal to but 180 degrees out of phase with that at the output end, which result may be obtained by the use of only two condensers CA, CB or CA, CC. In the two-section filter shown in Fig. 3, having a differential transformer T1, T2, at each end, the transmission through the piezoelectric crystals X1, X2 is balanced against that through the condensers C1, C2 for all frequencies outside the pass band, the balance being improved by the additional condensers CA, CB as in Fig. 1. The transformers T1, T2 allow the filter to be connected between unbalanced circuits, and they are tuned to the mid-band frequency by the provision of shunt capacities C3- C6. In order to correct for inductive unbalance, the couplings between the single winding W3 and the balanced windings W1, W2 are adjustable simultaneously in opposite senses, and preferably in addition the coupling between W3 and W1, W2 in series is adjustable. In the construction shown in Fig. 4, the winding W3 is carried by a tube 21 which is angularly adjustable in a circular slot 28 in a slide 22, and the latter is movable in longitudinal grooves within a tube 20 on which the balanced windings W1, W2 are wound.

Inventors

• 👤 Roger A Sykes

Bibliographic Details