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BELL SYSTEM TECHNICAL JOURNAL 



frequency, at first rapidly and then more slowly, being almost constant 

 after passing the frequency of 40 kilocycles. 



From the values of signal and noise so obtained, the signal-to-noise 

 ratio has been computed, and is also plotted in Fig. 2. The curve of 

 signal-to-noise ratio reaches a maximum near 44 kilocycles which 

 would seem to be the optimum frequency for daylight transmission 

 from the Rocky Point station to England. This is not strictly the 

 case, however, since there is some evidence that a phenomenon exists 

 which makes frequencies in the vicinity of 40 kilocycles particularly 

 poor for the transatlantic path. Data published by Anderson ^ tend 



30 40 50 60 



FREQUENCY - KILOCYCLES 



Fig. 2 — Variation of signal, noise, and signal-noise ratio with frequency. Trans- 

 mission from U. S. A. to England. 85.9 kw. supplied to antenna of Rocky Point 

 characteristics. 



to show that the field strength is distinctly subnormal in the vicinity 

 of 44 kilocycles and remains approximately constant from that fre- 

 quency up to about 60 kilocycles, where the observed values agree 

 fairly well with the calculations. (See later in this paper.) 



2. Band Width of the Transmitting Antenna. Since the output of 

 the transmitting set is at a high power level, the circuits coupling it 

 to the antenna must be of the simplest type to reduce the loss to a 

 minimum. In view of this requirement, the antenna constants largely 

 determine the band width of the antenna system. At frequencies 

 much lower than 60 kilocycles it was not possible to secure a sufficient 

 width of band even for commercial telephony from the Rocky Point 



' C. N. Anderson, "Correlation of Long Wave Transatlantic Radio Transmission 

 with other Factors Affected by Solar Activity," Proc. I. R. E., 16, 297; March, 1928. 

 In connection with reference above see Fig. 19, p. 315. 



