204 BELL SYSTEM TECHNICAL JOURNAL 



Even on the light loaded lines designed especially for good quality 

 on long repeatered circuits, the phase distortion is appreciable. The 

 nominal cut-off of these circuits is about 5,600. Fig. 6 shows the phase 

 characteristic of the transfer impedance of a section of side circuit of 

 19 Gauge H-44 cable only 20 miles long. On Fig. 10 is represented the 

 negative of the phase distortion, o-(a;), obtained by taking n = and 

 T = B((iOm)lcom where o)mj2ir is taken as the highest essential frequency, 

 in this case 4,000 cycles. 



In speaking of a pure sinusoidal wave of only one frequency, a 

 phase shift of more than l-w radians or one cycle would be meaningless 

 since every cycle is identical to the preceding and the following cycles. 

 To consider the variation of phase shift over a range of frequencies, 

 however, the total phase shift at any frequency as compared to that 

 at the lowest frequency of the range is required. 



III. Phase Distortion Correction 



1. Terminal Networks: Application to the Submarine Cable 

 The device of a terminal network having a compensating phase 

 distortion, that is, a network having the phase angle of transfer 

 impedance, 



<^(co) = [cor' - (t{w) ± Wtt], (12) 



over the frequency interval coi < w < c<;2 (r' being a constant), is 

 theoretically the most simple and, in practice, is probably the most 

 flexible and effective method of phase distortion correction. Such a 

 distortion corrective network, in series combination with the trans- 

 ducer in which the attenuation has been equalized, produces an 

 arrival curve 



I{t) = J- r ' i?(a,) COS [o^it - T - t') ^ d{u?) ± 7nr\dc^, (13) 



which is proportional to 



/(/ - r - t') 



provided, of course, that there is no reflection at the transducer 

 terminals. The constant phase angle db «x does not affect the 

 sinusoidal wave form but merely changes the sign of the wave if n 

 is odd. 



The terminal phase corrective network or phase compensator is 

 applicable, at least theoretically, to any type of phase distortion 

 correction and may be supplementary to other forms of correction 



