846 TITE BELL SYSTEM TECHNICAL JOURNAL, JULY 1953 



to one of the shapes, no network corrects except the one corresponding 

 to the original pattern of pilot deviation. 



If conventional regulator circuits were used with particular pilots 

 assigned to particular shapes the interactions would be intolerable. 

 Thus the computer removes the restrictions on the choice of shapes 

 imposed by regulator interactions. In turn this permits freedom in 

 changing shapes as system data improves. It is important to provide the 

 initial equalizers before adequate data on the system are available. As 

 the system grows in length the equalization must be improved but the 

 data improves also. Thus there is an economic benefit in providing a 

 flexible equalization plan which allows the earliest possible commercial 

 use of the system. 



Dynamic Equalizer Requirements 



Because temperature and aging variations can result in both gain 

 and loss variation with respect to the average transmission, the equalizers 

 must be capable of inserting both loss and gain compensation. Also, it is 

 extremely desirable that equal gain and loss settings for the equalizer 

 result in symmetrical transmission characteristics with respect to the 

 average. In a long transmission system, some of the sections mil insert 

 excess gain and others, excess loss. If the equalizer gain and loss char- 

 acteristics are symmetrical, the residue will be related to the system 



OUTPUT 

 (SHAPE ERROR) 



^W^ :5»o+' 



INPUT 

 (PILOT ERROR) / <> [> TO /U/3 SHAPE 



^1 (308 KC) a 



^2(2064 KC) 



^3 (7266 KC) 



TO Vf SHAPE 



Fig. 2 — Schematic of regulation system computer. 



