THE L3 SYSTEM — EQUALIZATION AND REGULATION 835 



tern that will permit attainment of the transmission objectives at all 

 service points and at all times. 



EQUALIZATION THEORY 



One of the steps in the solution of the general problem has been to 

 develop a ''theory" of equaUzation. This theory merely applies informa- 

 tion concepts to the equaUzation problem to determine what information 

 is required, when it is needed and how it may best be used. This theory 

 has stimulated the development of novel equalizer adjustment tech- 

 niques and has been of assistance as a guide to the attack on the general 

 problem. 



In order to equahze a system the man or machine who is to perform the 

 action must know what corrective steps are required, and for this he 

 must have some kind of information as to the present state of the system 

 and as to the desired state. Second, he must have the necessary tools to 

 convert the system from its present state to the desired state. Consider 

 the first problem, the determination of the corrective steps required. The 

 problem is to determine what we need to know, when we need to know 

 it and especially in what form we are able to utilize the information most 

 efficiently. 



We can assume we know the desired state of the system; which is 

 usually a constant loss with constant delay over the frequency range of 

 interest. As to the present state of the system we note that sufficient 

 information can never be obtained to equahze a system perfectly because 

 of the finite bandwidth of the system and because the system changes 

 with time. This is not a new fact, nor apparently a very important fact, 

 because the system need not be perfectly equalized for satisfactory trans- 

 mission of signals. It leads, however, to the converse idea, which is 

 important — namely, that out of this infinite amount of information 

 regarding the state of the system one should collect only the minimum 

 amount that is needed. This implies making no more measurements of 

 the state of the system than are absolutely necessary to perform the 

 correction to a degree permitting satisfactory transmittal of the signals. 

 The main purpose of this is, of course, to economize on time and effort 

 required to obtain information, but it should be noted that excess in- 

 formation may be a source of confusion to the equaUzation operator. 



To put this in the form of a rule, we have : 



Rule I 



Collect only that minimum of information as to the state of the system 

 as will permit equalization to the required degree for satisfactory transmission 

 of the signals. 



