806 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1953 



changes. By examining deviation curves for a number of specific net- 

 work designs, tentative choices were made of 50 per cent resistance 

 integral efficiency for the coupling networks and an allocation of about 

 half the cable slope to the pair of coupling networks and the remainder 

 to the feedback network. With an amplifier employing these networks 

 a detailed study was made of the noise and modulation penalties at 

 two frequencies resulting from misaUgnment in several lengths of line. 

 This study indicated that with certain refinements in the repeater design 

 the misalignment in twenty or more auxiliary repeater sections could be 

 tolerated with a signal-to-noise penalty of about 2 db which was judged 

 to be a reasonable allotment for this purpose. In addition, this study 

 brought out: (1) that randomizing the variations of an element between 

 its normal manufacturing limits resulted in a 4/1 reduction in the re- 

 quired misalignment allowance as compared with accepting large num- 

 bers of elements at one extreme of their limit; and (2) a small amount of 

 gain adjustment at each repeater in the vicinity of the high magnitude 

 television carrier would reduce the required misalignment allowance 

 by about 2/1. Refinements on this plan for handling misalignment had 

 to wait until the signal-to-noise and repeater design were crystallized. 

 However, the study referred to above provided a powerful tool for 

 evaluating proposed element deviations during the design period. 



When the exact signal levels and the most limiting modulation prod- 

 ucts became known and when the repeater characteristics and final 

 element deviations were determined it became possible to make a re- 

 fined study of misalignment in terms of the noise and modulation im- 

 pairment associated with specific signals and distortion products. At 

 this point performance margins associated with specific interferences 

 could be used to allow more or less misalignment of the particular signal 

 components forming the interference. Likewise, amplifier deviations 

 with specific frequency characteristics could be evaluated exactly in 

 terms of their effect on the number of repeaters between mop-up equal- 

 izers. By studies of this type it was determined that the "A" or mis- 

 alignment equalizers could be spaced at intervals not to exceed thirty- 

 two auxiliary repeater sections. 



2.232 Distribution of Element Deviations 



The methods of statistical (juality control used to monitoi* the process 

 of manufacture provided the necessary techniques for obtaining the 

 desired randomization of deviations. A companion paper^^ presents the 

 techniques that were developed to apply the broad fi(^l(l of knowledge 



