DISTORTION CORRECTION 



491 



Such an artificial line is made up of a number of different sections 

 whose various tandem combinations can build up by small steps a 

 considerable length of repeater section. A mechanism for switching 

 the various sections of artificial line in and out of a repeater section 

 might be operated by means of regulating apparatus which is auto- 

 matically controlled from circuit conditions existing on a single- 

 frequency pilot channel or channels. In Fig. 20 is shown a type of 

 network suitable for a section of such artificial line. It is equivalent 

 to Network 2>a, Appendix IV, from which it can be transformed. The 



i 6 



6 8 10 12 



Frequency {kilocycles per second) 



^14 



Fig. 20 — Sections of variable artificial line and their attenuation characteristics for 



carrier telephone circuits. 



following table gives the network elements for a group of such sections. 

 I need not discuss any of the design details here but shall merely state 

 that these sections were designed according to formulae in Appendix 

 IV from attenuation data which represent average requirements on the 

 open-wire pairs used for carrier systems. The frequency range for 

 these networks, 5.0-15.4 kilocycles per second, includes a lower group 

 of adjacent carrier channels each having a band width of about 2500 

 cycles per second. 



The attenuation characteristics of these individual sections are also 

 given in Fig. 20. By properly combining them the desired maximum 

 amount of artificial line can be obtained in equal steps, each step 

 corresponding to approximately 1 T.U. at the highest frequency of 

 the range. 



