N-1 CARRIER TELEPHONE SYSTEM 443 



along the faces of the terminal mounting framework uprights. Each duct 

 has an aperture opposite each horizontal row of equipment units. A ther- 

 mostat located in one of the terminal mountings starts the blower when 

 cooling is required. 



Repeater Units 



Two types of carrier repeater equipment units are used in the N-1 system. 

 They are identified by the designations HL (high-low) and LH (low-high). 

 The HL repeater receives signals at high group frequencies from the line, 

 translates them by modulation with a suitable carrier to low group fre- 

 quencies, then amplifies and regulates them for transmission at the desired 

 output level. The LH repeater functions similarly except it receives low 

 group frequencies and transmits high group frequencies. Each repeater pro- 

 vides for transmission in both directions and the two types are used alter- 

 nately along the line. 



A repeater equipment unit is made up of three subassemblies. In the HL 

 unit a right-hand high-to-low repeater and modulator subassembly for 

 east-to-west transmission and a left-hand similar subassembly for west-to- 

 east transmission are plugged into a common subassembly which supplies 

 the carrier for group modulation and the voltage regulator, all under a 

 common can cover. In the LH unit the right-hand and left-hand subassem- 

 blies are similar to those in the HL unit except low-to-high instead of high- 

 to-low. The common oscillator subassembly is identical in all repeaters. 



Repeater Mounting Arrangements 



Each repeater unit is plugged into a repeater mounting bracket which is 

 a small die casting equipped with three multipled connectors, one into which 

 the repeater is plugged and two for testing and in-service replacement of 

 the repeater. A terminal strip for external wiring connections, and span 

 adjustment pads, when required, are also mounted on this bracket. Four 

 of these mounting brackets are fastened to a shelf structure arranged for 

 relay rack mounting. With the four repeaters plugged in place, the entire 

 assembly occupies a vertical space of approximately 14 inches. The four- 

 repeater groups so constituted may be located in pole-mounted cabinets at 

 non-power supply points or on relay racks with associated power distribu- 

 tion panels at power supply stations. 



A total of twelve repeaters can be accommodated in a pole-mounted 

 cabinet, as shown in Fig. 19, together with order wire equipment and a 

 52-pair cable terminal. The terminal is located at the top of the cabinet 

 when the toll or exchange cable is aerial and at the bottom of the cabinet 

 when the cable is buried. The cabinet is made of sheet steel with the out- 

 side walls finished in white enamel to keep heat absorption to a minimum. 



