438 THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1951 



raised characters in a recessed area, instead of being applied by stamping 

 methods. The light weight of the aluminum die casting makes easier the 

 handling of a plug-in unit, particularly when the maintenance man is working 

 on a ladder. 



Terminal Equipment 



The terminal equipment as shown in Fig. 14 is designed for maximum 

 flexibility and mounts in the relatively small rack space of 19 by 40 inches. 

 Three such terminals can be mounted in a standard 11 -foot 6-inch relay 

 rack. A complete terminal includes 12 channel units, a transmitting group 

 unit and a receiving group unit. These units plug into a terminal mounting 

 fabricated of aluminum in natural finish, which is secured to the relay rack. 

 The terminal mounting, shown in Fig. 15, consists of two side members of 

 channel section with metal shelves welded between them to support the 

 equipment units. The twelve channel units are mounted five in each of 

 the two rows and two in the third row; the remainder of the bottom row is 

 used for the group units and for alarms and miscellaneous apparatus. The 

 terminal framework and wiring are the same for a terminal transmitting 

 the high group or one transmitting the low group. The fuses and alarm 

 relays for the terminal, and fuses and resistors for the power supplied to 

 an adjacent repeater, are located at the bottom of the terminal mounting. 

 Provision is made for mounting a span adjustment pad when required. 

 Both at the terminals and at the repeater points the receiving lines are 

 built out by these span adjustment pads so that the electrical length of 

 all lines is the same. The wiring between the connectors for the channel 

 units and for the group units runs within the shelf structure out to each 

 side of the bay and then extends up and down the mounting in the side 

 members. Extra connectors are multipled with the group unit connectors 

 to permit the replacement of these units without service interruption. All 

 connectors are mounted so that the wiring and the soldered connections are 

 readily inspected and maintained from the front of the relay rack, per- 

 mitting back-to-back mounting or mounting against a wall. All external 

 wiring is brought to terminal strips located at the bottom of the mounting. 



Channel Units 



Each channel unit contains the apparatus, including that required for 

 signaling, associated with one channel. The units for channels 1 to 12 differ 

 only in the receiving filter and in the crystal unit which determines the 

 channel carrier frequency. 



The apparatus is mounted in three subassembly frameworks which are 

 fastened together to form one unit, as shown in Fig. 16. The subassemblies, 

 shown in Fig. 17, are (1) the compressor (voice-frequency transmitting) 



