June 4, 1921 dellinger and whittemore: radio fading 249 



Three kinds of fading are observed : (1) Fading or swinging having 

 a period of swing of the order of one second or less. This is associated 

 with a given transmitting station. (2) Fading having a period of 

 the order of one minute. This is associated with a region which may 

 be that of either the transmitting or the receiving station. (3) Fad- 

 ing having a period of the order of one hour. This is associated with 

 a general direction of transmission or with a group of transmitting 

 stations. 



Signals from a given transmitting station may be received with 

 violent fading by some transmitting stations and simultaneously 

 with very small fading by others. Certain transmitting stations 

 are heard very well by many receiving stations in all directions on 

 some evenings, and heard by very few receiving stations or in only 

 one direction on other evenings. A given receiving station usually 

 "hears" certain transmitting stations with great fading and others 

 with little fading. 



Transmission wholly over water (both transmitting and receiving 

 stations far from land) shows little if any fading, while a narrow strip 

 of land intervening introduces fading, according to Nichols. Stations 

 near the coast fade worse than inland stations. 



For three successive nights, no short-wave signals were heard in 

 Virginia, though signals 800 meters or longer in wave-length came in 

 with usual intensity. The same phenomenon occurred one night 

 a week later in Baltimore and the District of Columbia. Later on, 

 the ninth radio district (the Middle West) suffered a similar blank. 

 During the District of Columbia anomaly the atmospheric conductivity 

 was very abnormal, changing from a very high to a very low value 

 without a corresponding change in the atmospheric potential gradient. 

 At 12:17 a.m. normal conditions abruptly returned, transmission 

 becoming very good. 



Signals on long wave-lengths, up to 23,500 meters, show very little 

 variation in intensity. There is little if any difference in the fading 

 from continuous wave and from spark stations on any wave-length. 



Strays. (Variation with place and time.) — Strays are more intense 

 in the summer than in the winter, and in the night than during the day. 

 They are more frequent and more severe in the tropics than in temper- 

 ate latitudes. 



At a given locality most strays come from a given direction. For 

 the northeastern part of the United States this direction is south or 

 south west. Strays are much less common in mid-ocean than near 



