The Bell System Technical Journal 



Vol. XVI October, 1937 No. 4 



Resistance Compensated Band-Pass Crystal Filters for 

 Use in Unbalanced Circuits 



By W. p. MASON 



In this paper are discussed several types of crystal band-pass 

 filters which can be used in unbalanced circuits. These types of 

 filters are all resistance compensated, i.e., the resistances associated 

 with the filter elements are in such a position in the filter that they 

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

 with the terminal resistances with the result that the dissipation 

 produces an additive loss for the filter characteristic and does not 

 affect the sharpness of cut-off attainable. It is shown that all these 

 types of networks can be reduced to three lattice types of crystal 

 filters, and the formulae for these three networks are given. A 

 comparison is given between the characteristics obtainable with 

 resistance compensated crystal and electrical filters and a conclu- 

 sion regarding their comparison given by V. D. Landon * is shown 

 to be incomplete. 



I. Introduction 



TN a recent paper ^ a description is given of a number of wave filters 

 -^ employing quartz crystals as elements. Most of these filters were 

 of the lattice type and hence were inherently balanced. For some 

 purposes, however, such as connecting together unbalanced tubes, it is 

 desirable to obtain a filter in an unbalanced form and it is the purpose 

 of this paper to show several forms for constructing resistance com- 

 pensated band-pass crystal filters which will give results similar to 

 those described previously. Another purpose is to give a numerical 

 comparison between the characteristics obtainable with resistance 

 compensated crystal and electrical filters. 



II. A Comparison of the Performance Characteristics of 

 Crystal vs. Coil and Condenser Filters 



In order to show the properties of resistance compensated crystal 

 filters it is instructive to give a comparison between the types of 

 characteristics 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. 



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