364 



THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1957 



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90 

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1 2 4 6 8 10 20 40 60 100 200 400 600 1000 



FREQUENCY IN KILOCYCLES PER SECOND 



Fig. 9 — PI Repeater amplifier gain-frequencj' characteristic. 



in system performance may vary considerably from that shown. The 

 repeater ampUfier gain frequency characteristic, plotted in Fig. 9, shows 

 a non-regenerative peak gain of the three-stage transistor amplifier of 

 80 db and a feedback gain characteristic of 50 db. This provides 20 db 

 or more of feedback over the transmitted band to produce the necessary 

 operating stability with temperature and power supply variations, and 

 a working value of modulation svippression. 



3.9 Repeater Regulation 



Repeater regulation will be furnished as an option where variations 

 in line loss exceed the terminal regulating range. It will usually be neces- 

 sary on sj-^stems employing more than one repeater in order to control 

 noise performance. Repeater regulation in the direction of transmission 

 from central office to remote terminal is controlled by the total carrier 

 power of the channels working on one system. In the opposite direction, 

 the repeaters will regulate on a low level carrier frequenc}'' pilot because 

 the channel carriers are not always present in that direction of transmis- 

 sion due to their signaling function. The pilot frecpencies are showTi in 

 Fig. 1. 



The repeater regulator, shown in schematic form in Fig. 10, functions 

 in much the same manner as the terminal regulator. The principal dif- 

 ferences between the two regulators arise from the requirement that 

 interchannel modulation must be appreciably less than 1 per cent in the 

 repeater. To limit the contribution of the repeater regulator to a small 

 value, the variolosser operates into a lower impedance and at a higher 

 control current than used in the channel regulator. 



