802 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1953 



in the gain and delay characteristics is straight forward if idealized 

 sinusoidal deviations extending across the whole band are assumed. 



In practice, the characteristics of the transmission deviations in a 

 long repeater system are very complex and therefore, the idealized 

 objectives are only a tentative guide in system design. Since we do not 

 have a thoroughly satisfactory method of evaluating complex echo pat- 

 terns, the exact nature of the final television mop-up arrangements will 

 be determined after subjective tests on the interfering effects of echoes 

 resulting from the complex transmission deviations of representative 

 links of the system. 



2.22 The Mop-Up Plan 



The deviations from ideally flat gain and delay transmission char- 

 acteristics may be classified in three broad categories; (1) fixed de- 

 viations; (2) slowly varying deviations; and (3) rapidly varying de- 

 viations. The distinction that is made between slow and rapid in the 

 last two categories relates to the frequency of adjustment needed to 

 meet system objectives. Those variations which require adjustment more 

 often than once a week are considered rapid and those requiring adjust- 

 ment at longer intervals are considered slow. 



Corresponding to each of the three classifications of deviations is a 

 set of equalizers, fixed, manually adjustable, or automatic under con- 

 trol of the pilot or a temperature sensitive element. Networks capable of 

 fulfilling the functions of each are distributed along the line according 

 to carefully prepared rules which enable system objectives to be economi- 

 cally met. The locations of these equalizers, their functions and general 

 characteristics are illustrated in Fig. 13. 



2.221 Fixed Equalizers 



To the extent that the auxiliary repeater is designed so that its nomi- 

 nal gain compensates for the loss of four miles of coaxial, it may be con- 

 sidered as the first step of fixed equalization. In addition to the amplifier, 

 the auxiliary repeaters are equipped with artificial lines, which are used 

 to build out the loss of short sections to the equivalent of four miles of 

 cable, and basic equalizers which provide for differences in the loss 

 characteristics of different types of ('able. 



The second and final step of fixed gain equalization is known as a 

 design deviation eciualizer. Its function is to correct accumulated de- 

 viations due to the fuilurc of the average auxiliary repeater to exactly 



