96 



THE BELL SYSTEM TECHNICAL JOUKXAL, JANUARY 1957 



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5 1.0 2 5 10 20 50 100 200 500 1000 2000 5000 10,000 



FREQUENCY IN KILOCYCLES PER SECOND 



Fig. 18 — • Mu Beta gain and phase. 



conditions of the particular network. The input and output coupling 

 networks and the beta networks enter directly into the insertion gain 

 and hence are held to very close limits. To ensure meeting these limits 

 elements which go into a particular network are matched and adjusted 

 as a group before assembly into the network. 



Repeater units are tested for transmission performance both before 

 and after closing. These tests consist of; mu-beta measurements (simul- 

 taneous measurements of gain and phase of the feedback loop); noise; 

 modulation; insertion gain at many frequencies; exact f requeue}^ of the 

 fault location crystal and crystal peak gain. Modulation and crystal 

 frequency measurements are made with the repeater energized at 225 

 milliamperes cable current and also at 245 milliamperes as a check on 

 the ultimate performance of the whole sj^stem initially and after aging. 



PERFORMANCE OF REPEATERS 



The phase and gain characteristics of the feedback loop of the repeater 

 are shown in Fig. 18. It will be noted that at the upper edge of the band 

 the feedback is a little less than the 33-34 db set as the objective. Addi- 

 tional elements could have been used in the interstages to increase the 

 feedback but the return per element is small. Since an}' element is a 

 potential hazard, the lower feedback is acceptable. 



