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BELL SYSTEM TECHNICAL JOURNAL 



this network is x/2 radians. Thus, it becomes necessary to use more 

 than one section on a long cable but it is also advantageous from the 

 point of view of flexibility of design. By adopting a standard unit, 

 for a 500-mile section of cable, for instance, the networks may be 

 readily accommodated to different lengths of line. 



FREQUENCY IN CYCLES PER SECOND 



Fig. 10 — Phase distortion correction on 20 mile 19 gauge H-44-25 loaded cable, 



< f < 4000 



It is interesting to observe that the analytical expression 



<^(co) = tan~^ 



ax 



1 + hx^ 

 is positive when < co < co„i, and zero when co = or Wm, provided 



(15) 



1 - wVc 



(18) 



Hence it will correct the phase distortion on the loaded cable as 

 shown in Fig. 6. The required phase shift is obtainable in the type 

 of network shown in Fig. 11. This network, however, has the dis- 

 advantage of tending to increase the attenuation distortion of the 

 loaded cable rather than to equalize it. 



When amplification is not required, it is undesirable to use the 

 device of an amplifier in each section of network for the sole purpose 

 of eliminating terminal reflection. As the characteristic impedance 

 of a transmission line may usually be regarded as a constant resistance 

 over the range of essential frequencies, the same purpose may be 

 accomplished by applying networks whose characteristic impedance 



