. The Bell System technical journal . Q 12 ^ ^ )^ a -z Z||=^Ro ^ ^ ^ ^ ^ ^ y^ ^ eo+* ^ ^ ^ ^ ^ / eo ,^ ^ ^ X ^ ^ ^ ^ , ^ eo-* ^ ^ ^ oooFig. 8—Variable equalizers with varying reference characteristics. A third simple network is shown on Fig. 9. Its properties are theconverse of those secured from the structures of Fig. 8. The referenceloss, ^0, is now a constant, while ip varies with frequency in a manner 3 See, for example, Distortion Correction in Electrical Circuits, O. J. Zobel,Bell Sys. Tech. Jour., July, 1928. 240 BELL SYSTEM TECHNICAL JOURNAL which depends upon the choice of Z. An a
. The Bell System technical journal . Q 12 ^ ^ )^ a -z Z||=^Ro ^ ^ ^ ^ ^ ^ y^ ^ eo+* ^ ^ ^ ^ ^ / eo ,^ ^ ^ X ^ ^ ^ ^ , ^ eo-* ^ ^ ^ oooFig. 8—Variable equalizers with varying reference characteristics. A third simple network is shown on Fig. 9. Its properties are theconverse of those secured from the structures of Fig. 8. The referenceloss, ^0, is now a constant, while ip varies with frequency in a manner 3 See, for example, Distortion Correction in Electrical Circuits, O. J. Zobel,Bell Sys. Tech. Jour., July, 1928. 240 BELL SYSTEM TECHNICAL JOURNAL which depends upon the choice of Z. An additional control of 0 canof course be obtained by the introduction of an auxiliary structure infront of the variable resistance. As in the previous example, theillustrative curves are drawn on the assumption that the characterizing sa^Ro. .*- = <+5^) Ro^2a 2a2-2a+i — 00+4. / X*^ / r a = Z-2^R0 1 \/ Y A eo ■^ ^ \ \ \ \. ^^ eo--^ UJQ Fig. 9—A variable equalizer requiring only one general impedance branch. impedance Z is a simple inductance. It will be observed that thecurves see-saw, the attenuation at certain frequencies increasingwhile that at other frequencies is decreased. This phenomenondepends upon the choice of the parameter a. It disappears when a isassigned either extreme value ^ or 1, and becomes most pronouncedat the intermediate value a = 1/V2. A similar effect can also be VARIABLE EQUALIZERS 241 produced in the networks we have already considered since, as equation(8) shows, the variable attenuation will change sign if the phase shiftof the auxiliary network is allowed to increase beyond 45°. In the fourth structure, shown by Fig. 10, both ^o and (^ are variable. fiAA y\ V I n Ro Z21 12 2211 0 ZmZ 11^21 ^Ro^^ 262422 / / r / y Z|i = ^^Ro / / 18 / y y / y •^ 16 UJCD UJ 14
Size: 2582px × 968px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
