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BELL SYSTEM TECHNICAL JOURNAL 



condenser filters. The quartz crystal filter considered here is shown 

 on Fig. 1. 



By using the balancing resistance Rx of Fig. 1 the crystal filter can be 

 made entirely compensated for coil resistance ; i.e. the resistance associ- 

 ated with the coils of the network is in such a place in the network that 



Fig. 1 — A bridge T quartz crystal filter. 



it can be effectively brought to the ends of the filter and combined with 

 the 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 be 

 used to terminate the filter completely, and introduces no loss. 



For the electrical filter, however, the dissipation introduced by the 

 electrical elements which replace the crystal is not compensated and 

 causes a considerable distortion of the pass band which becomes more 

 prominent as the band width is narrowed. To show this let us consider 



