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BELL SYSTEM TECHNICAL JOURNAL 



tiple channel system band pass filters will be employed. Fig. 9 shows 

 attenuation versus frequency characteristics of the high and low pass 

 filter combination. A study of these curves shows that the trans- 

 mission loss or attenuation in the high pass filter to frequencies trans- 

 mitted by the low pass filler is never less than 90 T.U., which corre- 



I'ig. 9 — Transmission Characteristic of llinh Pass anil Low Pass Filters 



ponds to a current ratio of approximately 30,000 or a power ratio 

 of appro.ximalely 9x 10", and the attenuation in the low pass filter 

 to the frequencies transmitted b\' the high pass filter is also equal to 

 or greater than 90 T.U. 



The characteristics of these filters are remarkable when it is con- 

 sidered that the frequency range in which they operate is higher 

 than that employed for multiplex carrier telephone systems, the 

 attenuation secured is higher than that ordinarily required for such 

 systems, and a power of 50 watts has to be transmitted through them 

 thereby introducing special problems in the design of the coils and 

 condensers. I'igs. 10 and 11 are fnmt ami l>ack \iews of one of these 

 filters. 



One of the uiuisii.il featines in the use of these lillers is the f.u I that 

 the position of the filters in the circuit is changed from time to time 



