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BELL SYSTEM TECHNICAL JOURNAL 



It is apparent that the improvement is a maximum in the middle 

 of the summer when the noise is high, and in the middle of the winter 

 when the field strengths are usually abnormally low. This is impor- 

 tant, since the greatest improvement is needed at each of these times. 



The monthly averages of variations of noise and of signal have 

 previously been published,^- *'- ^ and the generalizations given above can 

 be confirmed by reference to these articles. 



For calculating daylight radio transmission, several formulas have 

 been proposed.'"- ''• '- In Fig. 4 the heavy curve was calculated 



4700 4800 4900 5000 5100 5200 5300 5400 5500 

 DISTANCE FROM TRANSMITTER - KILOMETERS 



Fig. 4 — Transatlantic radio daylight field strength. Average of hourly observa- 

 tions during 1927. Corrected to 50 lew. radiated power — frequency 60 kilocycles 



from the empirical formula given by Espenschied, Anderson and 

 Bailey,^ and assumes a radiated power of 50 kilowatts. The great 

 circle distance from the transmitting stations used in the trans- 

 atlantic radio- telephone circuit to various receiving stations is indicated 

 by the name of the receiving station. The average of daily averages 



'Ralph Bown, "Some Recent Measurements on Transatlantic Radio Trans- 

 mission," Proc. Natl. Acad, of Set., 9, 221; July, 1923. 



^^ A. Sommerfeld, " Ueber die Ausbreitung der Wellen in der drahtlosen Tele- 

 graphie," Ann. d. Phys., 28, 665; 1909. 



•' L. F. F"uller, "Continuous Waves in Long-Distance Radio Telegraphy," Trans. 

 ^. /.£.£., J-/, pt. 1, 809; 1915. 



'^ L. W. Austin, "Quantitative Experiments in Radiotelegraphic Transmission," 

 Bull. Bureau of Std., 11, 69; Nov. 15, 1914. 



