VOLUME EFFICIENCY OF REPEATERED CIRCUITS 



529 



puted directly, it is necessary to make an allowance for the fact that 

 the circuit will vary from time to time. The principal variations in 

 an unregulated cable circuit are caused by temperature changes. In 



k = -^ = RATIO OF MAXIMUM TO R M S 



Fig. 3 — Probability of exceeding a maximum of X crosstalk units when the R.M.S. 



is Xt crosstalk units. 



a 1,000-mile circuit of 19-gauge H-44-25 four-wire facilities in aerial 

 cable in the northeastern part of the United States, for example, a 

 variation at 1,000 cycles of about ± 55 db from the average would 

 be normally expected due to temperature variations throughout a year. 

 About 35 to 45 per cent of this would occasionally occur in one day 



