706 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1952 



regards automatic equalization of attenuation slope with frequency, and 

 to obviate the necessity for additional line treatment. 



Some repeaters receive low group frequencies and transmit high group 

 frequencies for both directions. Other repeaters receive high group fre- 

 quencies and transmit low group frequencies. In N two kinds of repeaters 

 were required. In O the reversal of the filters in their sockets provides 

 both kinds of repeaters, and presents the proper designation to view. 

 A regulator is provided in each direction of the same kind as in the 

 group receiving unit. 



It should be noted at this point that the filters internal to the repeater 

 (as opposed to directional filters) differ from the filters used in the re- 

 ceiving group units. This is because the repeater always accommodates 

 line frequencies on both sides of the amplifier, while the receiving group 

 unit accommodates line frequencies on one side (which correspond to 

 the repeater line frequencies) but always must supply channel band 

 filter frequencies at the group amplifier output. 



Fig. 14 shows in somewhat greater detail than Fig. 13 the filter arrange- 

 ment for an OB repeater. 



TRANSMISSION CHARACTERISTICS 



The overall channel band width is illustrated in Fig. 15. The approxi- 

 mate frequency cutoffs are similar to N but for various reasons the 

 several channels may show somewhat greater differences. The O sys- 

 tem, being a single sideband system, has a filter cutoff at low (voice) 

 frequencies, which the N does not have. Differences may exist between 



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\r 



\f 



^_ 



Ab + Bf 



HIGH 

 PASS 



BAND 

 PASS 



BAND 

 PASS 



p}^4i§f "![>]- 



HD- 



BAND 

 PASS 



\f 



TO OA CARRIER SYSTEM OR TO 

 C CARRIER AND VOICE SYSTEMS 



Fig. 14 — Type-OB repeater filter arrangement. 



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60 76 



I 



BAND 

 PASS 



BAND 

 PASS 



TO LINE 

 FILTER 



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