THE N-1 CARRIER SYSTEM 19 



terminal uses three plug-in subassemblies: the low group unit, the high group 

 unit, and the oscillator unit containing 304 kc and 3700 cycle signaling 

 oscillators. The oscillator unit is always associated with the low-group 

 unit. 



In Fig. 8, (a), (b) and (c), typical group unit circuits are shown. The 12 

 channels combine in the resistance pads of the multiple on the terminal 

 frame and enter the transmitting group unit through the E filter. This filter, 

 as previously described, is used in both types of transmitting units to sup- 

 press transmission on harmonics of the channel carrier frequencies. The 

 noise generator at the input terminals supplies tube noise of equal ampHtude 

 at each high-group channel frequency to mask intelligible crosstalk in short- 

 toll or exchange circuits where the system noise may be low and the crosstalk 

 disturbing. A potentiometer controls the noise magnitude, which is always 

 set well below the tolerable limit. A slope equalizer in the high band is used 

 in the transmitting group unit to produce a compromise slope among the 

 channels at repeater points. Through its use input and output levels of 

 low-high and high-low repeaters are sloped either positively or negatively 

 by about 7 db, so that no one channel has more than 7 db disadvantage 

 from a noise and modulation standpoint. A compensating slope equalizer 

 in the receiving group unit restores the channels to flat band at its output. 

 The group modulator and 304 kc oscillator are alike in group units and 

 repeaters, whether used for low- to high-group band translation or vice 

 versa. The crystal oscillator differs only in minor respects from the channel 

 unit oscillator. The modulator is a double balanced ring type using four 

 yq inch diameter copper oxide discs. Group and repeater modulators employ 

 copper oxide to minimize noise. Low signal levels and high carrier level are 

 used in the group modulators to produce low interchannel modulation. As a 

 result good balance in the modulator and an output filter are needed to 

 suppress carrier leak. The two-stage feedback amplifier is alike in repeaters 

 and group units except in minor respects. 



Repeater 



A block schematic of a repeater station is shown in Fig. 9. The plug-in 

 repeater is shown within the dashed vertical lines. Mounted on the frame 

 and permanently wired are span pads, artificial line sections and deviation 

 equalizers when needed. The deviation equalizer is used only at low-group 

 frequencies and is placed in repeater input or output, whichever results in 

 locating the equalizer in an o&Lce instead of a pole cabinet. Resistance span 

 pads in 2 db steps from 2 db to 24 db are used to build out line sections 

 shorter than 8 miles at channel 1 frequency to 46 db loss in the low group 

 and 50 db in the high group. For line sections shorter than four miles, 

 artificial cable sections in two-mile and four-mile sizes are available. In 



