570 



BELL SYSTEM TECHNICAL JOURNAL 



CHANNEL MODEM EQUIPMENT 



GROUP MODEM 



BRACKETS J k 

 1 TO 5 IN < .-- , 

 FIG. 14 AS C 

 REQUIRED l." 



ODD EVEN 



HYBRID 

 COILS 

 AND NET- 

 WORKS 



120-KC 

 BUS BAR 



REGULAR 



CARRIER 



GENERATOR 



AUTO. 

 TRANS. 

 CIRCUIT 



EMER- 

 GENCY 



SPARE 



CARRIER 



GENERATOR 



120-KC 



AMPLIFIERS 



AND FILTERS 



Fig. 9 — Schematic showing the order of equipment at a terminal office. 



connected to one set of leads for each type of power, and even circuits 

 to another set. 



The voice frequency sides of the channel modem units have been 

 terminated in jacks which are located in a four-wire jack field mounted 

 in a voice frequency patching bay. From this point the four-wire 

 jack circuits are connected to the distributing frame for interconnection 

 on a four-wire basis with other channel equipment, voice frequency 

 repeater equipment, or terminating apparatus, as shown schematically 

 in Fig. 14. Voice frequency patching bays shown in Fig. 10-B may be 

 considered the equivalent of a secondary testboard. 



Voice frequency transmission measuring apparatus has been 

 mounted with the voice frequency patching bays. 



Main Repeater Office Eq)uipment 

 There are two types of installations at main repeater offices: {a) 

 flat gain regulation only, and {h) both flat and twist gain regulation 



