PLANNING AND OVER-ALL PEFRORMANCE 



25 



Variation of Over-all Transmission Loss 



The system has, of course, only been completed for a short time, but 

 the indications so far are that the standard deviation of the transmission 

 loss, as indicated by the 84.08-kc group pilots is well within the objective 

 of 1.5 db. Alarms operate when the received pilot level deviates by ±4 

 db and, so far, these alarms have not operated under working conditions. 



Frequency Characteristics of Telephone Circuits 



Fig. () shows the measured frecjuency characteristic of a typical circuit 

 in the two directions of transmission as measured in the through and 

 terminated conditions. Half the C.C.I.F. limits are met on most circuits. 



CHANNEL 

 5 6 



107 103 



99 95 91 87 83 79 75 71 67 

 FREQUENCY IN KILOCYCLES PER SECOND 



LONDON 



TO 



WHITE PLAINS 



WEST HAVEN 



TO 

 WHITE PLAINS 



PORTLAND 



TO 



WEST HAVEN 



SYDNEY MINES 



TO 



PORTLAND 



CLARENVILLE 



TO 

 SYDNEY MINES 



OBAN 



TO 



CLARENVILLE 



LONDON 



TO 



OBAN 



Fig. 5 — Frequency characteristic of typical London-New York channel group. 

 (Measured at group frequencies corresponding to 1,000 cycles.) 



