File:Bell telephone magazine (1922) (14569399220).jpg

Identifier: belltelephonemag16amerrich (find matches)
Title: Bell telephone magazine
Year: 1922 (1920s)
Authors: American Telephone and Telegraph Company American Telephone and Telegraph Company. Information Dept
Subjects: Telephone
Publisher: (New York, American Telephone and Telegraph Co., etc.)
Contributing Library: Prelinger Library
Digitizing Sponsor: Internet Archive

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ead to still further possibilities in these directions, but Camp-bell proved that the lattice structure was as effective as anysymmetrical structure that could be derived from combinationsof simple inductance and capacitance, thus greatly simplifyingthe task of later students. It is unfortunate that it does not seem possible to explain 29 BELL TELEPHONE QUARTERLY the action of a filter simply in mechanical terms. A tuned cir-cuit of inductance and capacitance is accurately analogous toa weight supported by a spring. One can devise a mechanicalfilter likewise from weights and springs in place of inductancesand capacitances. One can even observe that it acts as a wavefilter; but the explanation of its action is far too complicated totreat other than with mathematical equations, which we neednot go into here. When Campbells wave filter was first developed, no ex-tensive practical need was apparent for it, but it was neverthe-less quickly recognized as a tool of great potential value, and
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Fig. 4. Schematic of Generalized Lattice Network. the need for it was not long in coming. The earliest commer-cial use of a wave filter in a telephone transmission system wasmade in the first transcontinental line in 1915 to prevent sing-ing in telephone repeaters at frequencies above the voice range.A more extensive demand was created with the introductionof carrier telephone systems in 1916. From these beginningsthe use of filters has expanded with great rapidity. Today wefind the study of filters and related networks among the mostimportant and productive activities of the Laboratories. Sometwenty or more mathematically trained men now devote theirentire time to network design, and a staff of five mathematiciansis continuously engaged in research in this field. 30 THE EVOLUTION OF THE CRYSTAL WAVE FH^TER Some indication of the importance of filters and related net-works could be given by mentioning the large amount of moneyinvested in them, but in another sense their actual value f

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