THE N-1 CARRIER SYSTEM 9 



to prevent syllabic speech bursts from overloading circuits following the 

 compressor, and for slow recovery (30-50 milliseconds)^ so that the vario- 

 losser will introduce fixed loss over a syllabic interval. Too slow a recovery 

 time also is harmful, tending to leave the expandor at low loss after the 

 speech burst is over. Thus, the noise can be heard at the end of each syllable. 



The expandor in Fig. 3(b), like the compressor, consists of a variolosser, 

 an output amplifier, and a control circuit which rectifies the compressed 

 range of speech signals. Thus, the expandor control circuit is operated by 

 the expandor input speech signal and is called forward acting, while the 

 compressor control circuit is operated by the compressor output signals and 

 is called backward acting. The rectified syllabic envelope control circuit 

 currents in the compressor and expandor are made as near alike as possible 

 through choice of like circuit constants and levels, so that good tracking of 

 compressor and expandor variolossers will result. 



Integration of the compandor into the design of the N-1 system from 

 the start has yielded many advantages both from a line standpoint, and 

 in repeater and terminal circuit and equipment design. A listing of these 

 advantages follows: 



Line 



Operation to frequencies as high as 260 kc without need for far-end 

 crosstalk balancing. Crosstalk in cable increases about 6 db as the fre- 

 quency doubles and the ability to balance crosstalk becomes rapidly 

 unsatisfactory above 60 kc. The N system with satisfactory crosstalk for 

 200 miles would be satisfactory for only one or two miles without com- 

 pandors. 



Repeater spacing can be about 25 db longer (40% more miles) than with 

 no compandor, without limitations from near-end crosstalk or line noise. 

 Less precise balance in line and equipment against longitudinal noise can 

 be tolerated. 



Longitudinal noise suppression coils are eliminated in voice pairs not 

 used for carrier at repeaters in telephone offices. 



Reflected near-end crosstalk requirements are eased markedly, thus '^ 

 permitting much less precise equipment impedances. 



Repeater 



Poorer modulation can be tolerated, thus allowing 25 db less feedback, 

 25 db less non-regenerative gain and fewer repeater tubes. As many as 

 25 repeaters can be tolerated in tandem. Without the compandor even 

 one repeater would make the system unsatisfactory from this standpoint. 

 Repeater directional filter discrimination requirements are reduced by 

 about 25 db. 



