THE L3 SYSTEM — EQUALIZATION AND REGULATION 839 



the data should be in the same form; a set of numbers (or their equiva- 

 lent) representing equalizer changes. 



Probably the most useful result of this theory of equalization has 

 been the conclusion that mechanization of the equalization process, 

 particularly in regards to computational techniques, permits substitu- 

 tion of simple logical methods for inefficient trial-and-error adjustment 

 processes. This led to the use of an analog computer in the regulation 

 system and, for manual equalizers, the development of measuring cir- 

 cuits that read directly in terms of equalizer adjustment error. 



Equalization 



location and function of equalizers 



The location of equalizers in the L3 system when only telephone is 

 transmitted is shown in Fig. 1(a). Combined telephone-television equali- 

 zation is shown on Fig. 1(b). When telephone and combined systems 

 use the same spare Hne, that line is equipped for television. The general 

 features of the main-repeater layout have been described in a com- 

 panion paper. ^ The detailed layout of equalization is designed to meet 

 the requirements of both telephone and television service and the need 

 for flexibility in television network arrangements. In addition, switch- 

 ing of telephone or television service to a spare line must not appreciably 

 degrade service. 



Switching sections longer than 120 miles must be provided with an 

 intermediate step of equalization to prevent excessive signal misalign- 



'1 EHf^^ — — X EHD— 



Q &^- ^ EK?^' 



.-125 MILES- J< UP TO 125 J<— OFFICE »|*- -.,1;'^c7SJ??k,c— 4« OFFICE-->l 



OF LINE ^^ MILES OF LINE I H^ MILES OF LINE I ' 



OFFICE 



EQUALIZER ,r.^„^,^ 



FIXED__.»H , , , FIXED _..,j . , , 



DELAY \4 U L TELEVISION DELAY fl H ^ H 



P n rU--- PATH V- ' ' ^ 



H Be€h^4J L>^ ^IHIh^<] D-"- 



l~^ I 1 r^^BRANCHING I 1 



I O h^ ' FILTER I— |oJ— ' 



^TELEPHONE 

 PATH 



Q S^3&^ " EH5>E}-^ 



Pig 1 _ Typical equalizer locations in (a) telephone and (b) combined systems. 



