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BELL SYSTEM TECHNICAL JOURNAL 



neglected. The presence of such equalizers in the circuit for program 

 transmission did not influence the design of the phase correctors. 

 However in considering the design of the equalizers the particular 

 structure used was chosen on the basis of its giving a minimum amount 

 of phase distortion. 



Phase Distortion in Other Communication Systems 



Phase distortion has for some time been considered a real problem 

 in submarine cable telegraphy. If the highest reversal frequency of a 

 telegraph signal is /„ it has been found expedient to correct for both 



14 



12 

 10 



in 



UJ 

 LU 



a. 

 o 



LU 

 Q 



Z 



I 

 IT) 



in -2 

 < 



I 

 a -4 



-10 



200 



400 



600 600 ipOO ipOO 3,000 



FREQUENCY IN CYCLES PER SECOND 



5.000 



7.000 



9p00 



Fig. 26 — Insertion phase characteristics of repeating coil, input transfornier and 

 output transformer used in repeater shown in Fig. 25. 



amplitude and phase distortion over a frequency range of from zero 

 to between 1.4 and 1.6 /„. More phase distortion can be tolerated 

 when the signal is read by the operator from a siphon recorder slip 

 than for automatic printing. In the case where fv is 60 cycles per 

 second a 45° departure (at 60 cycles) from the low frequency character- 

 istic if continued as a straight line it has been found in some cases to 

 cause errors to be printed. 



While no two telegraph cables are alike all except very short ones 

 require that some means of phase correction be incorporated in the 

 terminal apparatus. Although the general principles of correction 

 have been investigated mathematically and the results have been very 

 useful as a guide in indicating the relative effects of factors involved, 



