JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. 11 * JUNE 4, 1921 No. 11 ' 



RADIOTELEGRAPHY.— i?aJ/o sigfial fading phenomena.' J. H. 

 Bellinger and L. E. Whittemore, Bureau of Standards. 



INTRODUCTION 



In actual communication by radio, many difficulties are encoun- 

 tered that would not be expected by one who is familiar only with the 

 rather precise and clear-cut theory of the subject in books. Some 

 of the phenomena in radio-frequency circuits may be represented 

 accurately by ordinar}^ alternating -current theory, the m-athemxatical 

 treatment being even simplified at radio frequencies. However, the 

 phenomena of transmission of radio waves from one place on the earth's 

 surface to another are of quite a different kind, and involve so many 

 variables that they are very difficult of analysis. 



The difficulties which are peculiar to the transmission and reception 

 of the waves in actual radio communication may be divided into: 

 (1) "fading" or "swinging" of the received wave intensity; (2) strays; 

 and (3) interference from other radio stations whose signals it is not 

 desired to receive. 



"Fading" is the rapid variation of intensity of the signals received 

 from a given transmitting station, all circuit arrangements at the 

 transmitting and receiving stations remaining constant. It is char- 

 acteristically a night phenomenon. 



"Strays" are electrical disturbances giving rise to irregular inter- 

 fering noises heard in the telephone receivers of a receiving circuit. 

 They are present in some degree at all times, though they are usually 

 worse at night and in the summer time. 



Interference from other stations differs from the other phenomena 

 in that it can be eliminated. The means by which this may be done 



' Presented before the Philosophical Society of Washington, January 29, 1921. Pub- 

 lished by permission of the Director, Bureau of Standards. Received May 5, 1921. 



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