. The Bell System technical journal . f resistance compensated crystalfilters it is instructive to give a comparison between the types ofcharacteristics which can be obtained by using crystal and coil and Electrical Wave Filters Employing Quartz Crystals as Elements, W. P. Mason,B. S. T. J., July, 1934, p. 405. 423 424 BELL SYSTEM TECHNICAL JOURNAL condenser filters. The quartz crystal filter considered here is shownon Fig. 1. By using the balancing resistance Rx of Fig. 1 the crystal filter can bemade entirely compensated for coil resistance; the resistance associ-ated with the coils of
. The Bell System technical journal . f resistance compensated crystalfilters it is instructive to give a comparison between the types ofcharacteristics which can be obtained by using crystal and coil and Electrical Wave Filters Employing Quartz Crystals as Elements, W. P. Mason,B. S. T. J., July, 1934, p. 405. 423 424 BELL SYSTEM TECHNICAL JOURNAL condenser filters. The quartz crystal filter considered here is shownon Fig. 1. By using the balancing resistance Rx of Fig. 1 the crystal filter can bemade entirely compensated for coil resistance; the resistance associ-ated with the coils of the network is in such a place in the network that y 1 ■ •-1 h ^JOOC> T 1-2 o \ ( C,=r Rx> Fig. 1—A bridge T quartz crystal filter. it can be effectively brought to the ends of the filter and combined withthe terminal impedances with the result that the effect of the dissipa-tion in the coils is only to produce an additive loss for the filter charac-teristic and does not affect the sharpness of cut-off attainable. In fact. Fig. 2—Electrical network equivalent to crystal filter of Fig. 1. if the filter works into a vacuum tube the dissipation in the coil can beused to terminate the filter completely, and introduces no loss. For the electrical filter, however, the dissipation introduced by theelectrical elements which replace the crystal is not compensated andcauses a considerable distortion of the pass band which becomes moreprominent as the band width is narrowed. To show this let us consider RESISTANCE COMPENSATED BAND-PASS CRYSTAL FILTERS 425 the network of Fig. 2. In analyzing such networks it is usually moreconvenient to reduce them to their equivalent lattice form and applynetwork equivalences holding for lattice type networks. This can bedone by applying Bartletts Theorem ^ which states that any networkwhich can be divided into two mirror image halves can be reduced to anequivalent lattice network by placing in the series arms of the lattice atwo-terminal im
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