1074 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1956 



on this is the same signal after traversing a 1.75 mile length of line and 

 the same equalizer. Shortening the line results in the transmitted pulses 

 having higher peak amplitudes and narrower widths. Faulty high fre- 

 quency equalization of the shorter lengths produces the short tail 

 following the pulse. It is interesting to observe that the transient tail 

 due to the low frequency cut off has not changed appreciably as the 

 line was shortened. This is to be expected since it can be shown that 

 the energy of the low frequency cut off transient is concentrated in low 

 frequency end of the transmission spectrum. In this region changes in 

 the length of the line, or changes in the primary constants will result 

 in inconsequential changes in attenuation and phase as is shown on 

 Fig. 6. If the quantized feedback is adjusted for the worst condition, 

 i.e., the highest temperature likely to be encountered, it will not need 

 to be changed with lower temperatures. 



4.0 ERROR PRODUCTION BY EXTRANEOUS INTERFERENCE 



A knowledge of the performance of a regenerative repeater with 

 various types and amounts of interference added to the input signal is 

 important. Consequently a study of such errors produced in one of 

 these repeaters was undertaken. Two general types of extraneous inter- 

 ference was used in this study. The first is impulse noise, the type which 

 is produced by telephone dials, switches, lightning surges and crosstalk 

 from other pulse systems. The second is sinusoidal noise, the type which 

 come from power line or carrier crosstalk. This interference may affect 

 the regenerated output in a number of ways. It may produce a phase 

 shift or "jitter" in the output; cause a pulse to be omitted; or cause a 

 spurious pulse to be inserted in the signal code. The phase jitter will be 

 largely removed by timing regeneration in subsequent repeaters, but 

 omission and most insertion errors will be carried through the remaining 

 repeaters, causing distortion in the decoded signal. 



Plate IV — Superimposed picture of the outputs of 2.3 and 1 .75 miles of 19 gauge 

 cable with identical injjuts. 



