710 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1952 



cuits, perhaps to equalize this phase shift in order to prevent serious 

 reduction of signal output, or variation in channel net loss with fre- 

 quency. No such concern applies to O. 



In regard to filter characteristics, it seems obvious that complete 

 coverage is not feasible in this description. Instead typical curves only 

 will be shown. 



Fig. 20 shows the general characteristics of filters for separating the 

 wanted sideband from the carrier and unwanted sideband. The trans- 

 mitting and receiving filters have similar shapes. The carrier pick-off 

 filter characteristic is shown in the same figure. Fig. 21 shows the filter 

 characteristics for separating the voice and signaling (3700 cycle) func- 

 tions. 



Another filter case of interest is the line filter for separating, for ex- 

 ample, the OA system from the OB system, and from the OC and OD 

 systems, as well, if they are employed. Fig. 22 shows the configuration 

 and loss characteristics of the Gl (537A or 538A) filter. A Cb directional 

 filter (530A) characteristic is shown on Figure 23. This filter assembly 

 includes two filters to accommodate the OB high and low group assign- 



CHANNELS 



TRANS 

 BAND- 

 PASS 



WANTED SPEECH 



UNWANTED 

 CROSS -TALK 



REC 

 BAND- 

 PASS 

 FILTERS 



5432 10 12345 



FREQUENCY IN KILOCYCLES PER SECOND (FROM CARRIER! 



Fig. 20^T3^pical channel band and carrier pick-off filter characteristic. 



