GB549926A - Attenuation equalizer - Google Patents

Abstract

549,926. Impedance networks. STANDARD TELEPHONES & CABLES, Ltd. March 28, 1942, No. 4180. Convention date, Oct. 24, 1940. [Class 40 (iii)] A variable attenuator comprises a number of sections connected in parallel at their input ends and coupled at their output ends to a high impedance load by a condenser potentiometer. The sections are preferably of constant resistance type and their loss characteristics are linear over the working frequency range, the loss being the same for all the sections at some frequency at the lower end of the range, as indicated in Fig. 5. Sections 2, 3 may be of the bridged-T type shown in Fig. 2 having a rising characteristic and sections 5, 6 may be of the bridged-T type shown in Fig. 3 having a falling characteristic, while section 4 is a simple resistance pad giving uniform loss. A further section 1 similar to section 2 may be connected in tandem therewith, the combination having a characteristic curve 11 slightly displaced from the common point 39 of the curves of the other sections. Sections 1, 3, 5, 6 are terminated in their image impedances and resistances 8, 9, 10 may be added to adjust the loss at certain frequencies. Section 7, which gives a gain over a part of the working range may be designed as shown in Fig. 4, in which the series and shunt impedances are connected by the relation Zc(Za+Zb-Ro)=Ro<2>. The condenser potentiometer comprises fixed plates 31-37 connected to the various sections and a plate 30 which may be moved manually or automatically, for example, under the control of a pilot current, to bring it opposite any one or an adjacent pair of the fixed plates.