RADIO BROADCAST COVERAGE OF CITY AREAS 



119 



intended to indicate the appearance of variations in the signal intensity 

 which occur at the greater distances, particularly at night, and which 

 are known as "fading." 



Distance 



/ Area oF Fair to Poor Reception. 



Fig. 1 — The attenuation of broadcast waves in reference to the areas served 



The evidence of recent researches, particularly those made at short 

 wave-lengths, indicates that these fading variations are due to radiant 

 energy which has left the earth's surface at the radio transmitter and 

 has been reflected or refracted back to the earth's surface from a 

 conducting stratum in the upper atmosphere. At broadcast fre- 

 quencies the reflected wave component is observed at night but has 

 not been noticed during the day. At locations close to the trans- 

 mitting station the effect of the reflected component is negligible as 

 compared with the strength of the directly transmitted waves. At 



