26 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1951 



power. Low-group output repeaters and terminals have carrier outputs 

 sloped from —12 to —5 dbm with total carrier power of +3 dbm. Trans- 

 mitting group input carrier levels of —53 dbm and receiving group output 

 carrier levels of —5.5 dbm are alike in low-and high-group terminal units. 



+B 



VOLTAGE 

 VOLTAGE REGULATOR 

 REGULATOR TUBE FILAMENT 

 CURRENT /- — ^ CURRENT 

 CONTROL / \ CONTROL 



OSCIL- 

 LATOR 

 TUBE 



ITHERM-^ 

 ISTOR 



W~E 

 REPEATER 



Fig. 12 — Repeater power regulator — Distributer Circuit. 



Strengths of signals at various levels before and after the compressor can 

 be simply calculated from the following equation: 



P - Z 



+ Lc^ 2.5, 



where P and L are the power in dbm and level in db before the compressor 

 and Pc and Lq the corresponding values after the compressor. 



Power Supply 



The power supply at terminals is obtained from -f 130 volt and —48 volt 

 batteries. All vacuum tubes have 20- volt heaters used two in series across 

 an adjusted 40 volts from the 48-volt battery. Repeaters are supplied 

 either locally from +130 volt battery or over the simplexes of the cable 

 quad to pole-mounted points using +130 volt and —130 volt battery. 

 A series parallel arrangement of tube and thermistor heaters in the repeater 

 obtain closely regulated voltage from a gas tube control circuit. This ar- 

 rangement is shown in Fig. 12(a). So closely are the tube heater voltage and 



