GB613709A - Improvements in variable equalisers for signal transmission systems - Google Patents

Abstract

613,709. Impedance networks. GENERAL ELECTRIC CO., Ltd., and COLLETT, E. W. June 26, 1946, No. 19128. [Class 40 (viii)] An equalizer consists of a four-terminal network having an iterative impedance Z0 which is substantially purely resistive and comprises one or more series impedance elements of value Z1 and one or more shunt impedance elements of value Z2 such that Z1 Z2=Z0<2>, wherein means are provided whereby the value of Z1 can be changed to a number of values K1 Z1, K2 Z1, &c. and whereby the value of Z2 can be changed to a number of values 1/K1 Z2, 1/K2 Z2, &c., where K1, K2, &c. are different, and preferably consecutive, integers or the square roots of such integers. This inverse variation of Z1 and Z2 alters the propagation constant of the network by integral multiples and permits the equalizer to be adjusted to smooth out the transmission on a route consisting of any desired number of standard cable lengths. In the first embodiment, Z1 consists of an inductance L1, condenser C1 and resistance R1 coupled by a transformer T1 having tapped windings over a pair of impedances Z0. The impedance Z2 comprises a similar inductance L2, condenser C2, resistance R2 and transformer T2. Variation may be obtained by tapping the resistances instead of using transformers. The second construction shown is in effect a lattice network as, though there is only one impedance Z and one Z2 they are coupled in a network by tapped transformers T1 and T2, each with two primary windings and together forming the lattice.