CONQUEST OF DISTANCE BY WIRE TELEPHONY 391 



mediate points. In this connection, it should be remembered that the trans- 

 continental circuits were not through circuits, ready upon call, but were 

 built up by switches at two or three intermediate points as required. 



It is of interest to note that the change from three repeaters to six re- 

 peaters did not significantly affect the overall transmission performance. 

 The gains in the individual repeaters had to be reduced in order to avoid 

 objectionable interaction effects. 



The transmission performance and circuit data given below apply to the 

 New York-San Francisco circuits, having sbc vacuum tube repeaters in 

 tandem: 



Over-all Length 3359 miles 



Transmission Losses 



Bare Line 53 db 



Apparatus 7 db 



Over-all, Line and Apparatus 60 db 



Total Repeater Gain 40 db 



Net Equivalent 20 db 



Over-all Transmission Time 0.067 second 



The net equivalent above given is a dry weather value. Under bad weather 

 conditions the line loss approximately doubled. Adjustment of the re- 

 peaters, made manually, was required to keep the overall equivalent within 

 reasonable bounds. 



The transmission band that was effectively transmitted ranged from about 

 350 to 1250 cycles, defining the transmission band as that between the 

 lowest and highest frequencies whose transmission was not more than 10 

 db higher than that of the transmission of 1000 cycles. At frequencies 

 between 400 and 1000 cycles, the over-all loss was appreciably less than at 

 1000 cycles. At frequencies above 1250 cycles, approximately 50% of the 

 theoretical loading cut-off frequency, the line losses including the loading 

 coil losses piled up so as to effectively suppress transmission. The excess 

 transmission losses at the low voice frequencies were due to losses in the line 

 terminal apparatus (repeating coils, composite sets) and in the repeater 

 auxiliary apparatus. Although the 900-cycle frequency band effectively 

 transmitted by the transcontinental circuits was only about ^ as wide as 

 that required by the present standards for long distance transmission, it 

 was acceptable to the early users of the service, and did not noticeably 

 handicap the public interest in the large number of country-wide demonstra- 

 tions that were made in the "Hello, Frisco!" era. 



In the concluding section of his report to the American Company stock- 

 holders for the year 1914, President Vail appraised the siirnificance of the 

 transcontinental line and related developments as follows: 



"it is a long step from a hardly intelligible telephonic conversation between 

 two rooms, to a perfectly easy, low-voiced conversation between the extremes 



