GB793165A - Improvements in adjustable correcting networks - Google Patents

Abstract

793,165. Adjustable equalizing networks. COMPAGNIE INDUSTRIELLE DES TELEPHONES. Jan. 6, 1956, No. 511/56. Class 40 (8). An adjustable attenuation network consists in an improvement in the bridged-T network of Specification 508,341, [Group XL] (reproduced in Fig. 2) in which the networks Q1, Q2 are replaced by a cutall lattice network Q (Figs. 3, 4) of mean characteristic impedance Ro which is connected on one side across the bridging resistance R1 and coupled on the other side to the shunt branch of the bridged-T through series resistance R2 and a transformer of ratio α. In the known network of Fig. 2 the terminal resistances Ra, Rb are adjusted so that the impedances of the networks Q1, Q2 remain constantly inverse with respect to R, the characteristic impedance of the bridged-T. The condition R1R2 = R<SP>2</SP> is also necessary. The lattice network Q having series branches Z, R<SP>2</SP>0/Z and variable diagonal branches Ra and Rb = Ro/Ra may replace the networks Q1, Q2 under the condition that α<SP>2</SP> = R<SP>2</SP>/R1R2 = R<SP>2</SP>/R<SP>2</SP>o, which requires that R1R2 = R<SP>2</SP>o. The bridged-T will then have a constant characteristic impedance R. The Specification includes a detailed analysis of the network in which it is shown that'the attenuation comprises a fixed portion and a variable portion proportional to cos2B, where B is the phase shift of the reduced impedance z = Z/Ro. At frequencies at which B is an odd multiple of #/4, cos2B is zero and the total attenuation is equal to the fixed portion; there are therefore pivot points in the attenuation curves. If a pure reactance is chosen for Z the pivot points correspond to the values Œj of the reduced reactances. There may be any number of them and the number is reduced to one for an inductance or a capacitance. Maximum variations occur at the frequencies for which B = n#/2, that is, at the zeros and poles of Z. The input and output terminals of the network Q may be reversed and Rb made equal to R<SP>2</SP>o/Ra. This halves the number of regulating resistances. The bridged-T network may be replaced by the equivalent hybrid network of Fig. 3. In this network α<SP>1</SP> = Ro/2R, R1<SP>1</SP> = “#2R,R1# and R2<SP>1</SP> = R<SP>2</SP>o/4#2R,R1#, where the double-line brackets indicate that the enclosed elements are connected in parallel. The Specification gives detailed examples of several networks with numerical values of components. Specification 469,067, [Group XL], also is referred to.