PHASE DISTORTION AND PHASE DISTORTION CORRECTION 219 



evident from a consideration of the duration of the transient distortion 

 that the correction is not perfect, although it is appreciably better 

 than that afforded by either lattice loading or a combination of 

 lattice and coil loading. In Fig. 19 the delay in the time of building-up 

 of any frequency co/27r over the time of building-up of a direct current 

 is shown for these different systems. Since the physical desideratum 

 is a minimum constant delay for all frequencies, and the delay is 

 quite sensitive to small deviations from the distortionless steady state 

 phase angle, the former is probably a better basis of design and 

 comparison than the latter. 



2 4 



8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 

 FREQUENCY IN HUNDRED CYCLES PER SECOND 



Fig. 20 — Transient distortion on 50 miles of 19 gauge light loaded cable 



Suppose that it is required to reduce the delay at 4,000 cycles to 

 the value or to less than the value of the delay on the uncorrected 

 cable at 3,000 cycles. The procedure will be to solve equation (30) 

 for -{LC in terms of N and the required value of T — To at the given 

 frequency coa/27r = 4,000, substitute these values in equation (30) 

 and compute T — Tq over the essential frequency range. It is 

 immediately apparent from Fig, 20 that the improvement at the 

 higher frequencies is at the expense of the intermediate frequencies 

 where the delay is reduced too much. This disadvantage is lessened 

 by increasing the number of sections but this method is uneconomical 



