678 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1952 



§30 



25 



O 20 



I- 

 a. 

 O 



I- 



•n 15 



t; 10 



-65 -60 



-40 -35 -30 -25 -20 

 RECEIVING LEVEL IN DBM 



Fig. 6 — Telegraph distortion vs receiving level. 



A rear view of the channel terminal with the send frequency unit 

 removed is shown in Fig. 8. With both frequency units in place, the 

 rear of the channel terminal is almost completely enclosed. When they 

 are removed, the wiring and apparatus terminals of the basic channel 

 terminal are readily accessible for test and repair. 



Tube sockets, potentiometers, test points, switches and the inductor 

 of the low-pass filter are mounted on the front panel. Small resistors, 

 capacitors, and germanium diodes are assembled on a plastic "ladder" 

 which is mounted vertically in the space between the frequency units. 



As shown in Fig. 9, three channel terminals may be mounted abreast 

 on a welded metal frame which is fastened to any of the standard bay 

 frameworks designed to accommodate 19-inch mounting plates. The 

 unit mounting frame carries the multicontact receptacles into which the 

 channel terminals are plugged. Twenty-four channel terminals may be 

 mounted on an ll^-foot relay rack, with line coils and certain auxiliary 

 equipment. 



Where arrangements for s\vitching between half and full-duplex opera- 

 tion are required, duplex switches for a number of channel terminals 

 are mounted on a narrow plate between the channel terminal mounting 

 frameworks. 



Loop rheostats, when required, may be mounted adjacent to the 

 channel terminals or in a loop pad bay along with other loop rheostats 

 that may be associated with electronic loop repeaters. The latter arrange- 



