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BELL SYSTEM TECHNICAL JOURNAL 



A completed filter is shown in the photograph of Fig. 13, while the internal 

 arrangements of one portion of the assembly are shown on Fig. 14. 



Fig. 14 — Interior view of one portion of the assembly of the band ehmination filter. 



Phase Simulating Network 



When program rearrangements at a branching point are required, the 

 band elimination filter must be switched into or out of the through trans- 

 mission path. This transfer is accomplished without opening the through 

 path. Thus, for a brief time during the switching interval, message chan- 

 nels are transmitted simultaneously through the filter and the non-blocked 

 circuit. A large phase difference between the two parallel paths is intro- 

 duced by the filter which, in the absence of phase correction in the through 

 circuit, could cause errors in the transmission of voice frequency telegraph 

 signals. Therefore a network having phase shift similar to that of the filter 

 over most of the message range is provided in the through circuit. 



