282 BELL SYSTEM TECHNICAL JOURNAL 



At 30 kc, this figure represents a variation in the location of the 

 attenuation characteristic of ± 60 cycles. However, variations in the 

 effective resistances of the filter coils, and variations in the reflection 

 loss caused by small changes in the filter impedance produce changes 

 in the attenuation of a filter which must be taken into consideration. 

 The sum of these variations amounted to about ±15 cycles. The 

 ± 60 cycle precision at 30 kc, the highest frequency of the type "C" 

 system, became, therefore, ± 75 cycles; a figure well within the ±125 

 cycle maximum shop limit required by the system, and considerably 

 less than the ± 300 cycle limits formerly obtainable. 



The adoption of this method of filter construction has made it 

 possible to realize in commercial manufacture the high precision of 

 characteristic location which was formerly limited to laboratory 

 construction. 



