1454 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1957 



Table I — Summary of Various Data System Characteristics 



Telegraph Comparison 



43A1 Channel 



+ 10ttl 



0tt|-10tt|±5 |±60 

 -12 Channels- ) 



450 

 (6 Channels) 



1100 

 (15 Channels) 



Speech Comparison 



Speech 



-t-10 +10 +10 



±10 



50 



* High grade performance; i.e., less than 1 error per 100,000 bits. 



** High figure assumes accurate delay correction and control of nonlinearity. 



t Depends on precise line-up of filter and carrier. 



ft Allowance for peak factor of 12 frequencies. 



VSB = Vestigial sideband; DSB = Double sideband; FS = frequency shift. 



This impairment is here assumed to be about 3 db. A rather larger 

 impairment has on occasion been assumed by other authors.' In the 

 case of the telegraph system some arrangements for merging the signals 

 in parallel channels into a single high speed channel require a certain 

 exactness in timing correlation. The need for this may be overcome by 

 the use of a small amount of data storage in the receiver of each channel. Jj 

 The delay distortion figures quoted in the table assume no need for this 

 timing exactness. As in the other part of the comparison twelve chan- 

 nels are assumed. 



The last two columns indicate the bit rate that can be expected of the 

 various systems, first per 1,000 cycles of band, and second for a tele- 

 phone facility of somewhat narrow (but frequently encountered) band- 

 width. Some of these figures assume a careful control of delay distortion 

 and of nonlinear distortion. In the 1,000-cycle band only six channels 

 of the telegraph assumed may be accommodated. In a 2,500-cycle band 

 the number can be extended to 15. The band that can actually be used 

 for telegraph, over a given facility, depends upon the nature of that 

 facility. 



