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BELL SYSTEM TECHNICAL JOURNAL 



increasing distances the directly transmitted waves die away to very 

 low values and the indirectly transmitted waves begin to show up 

 and appear to become controlling at the longer distances. The 

 fluctuations themselves appear to be due in part, if not entirely, to 

 variations in the reflected waves themselves, resulting perhaps from 

 fluctuations in the conditions of the upper atmosphere. 



Thus, it seems clear that radio transmission involves wave com- 

 ponents of two types: one which delivers directly to the receiving area 

 immediately surrounding a broadcast station, a field capable of giving 

 a reliable high grade reception; and another transmitted through 

 the higher altitudes which permits distant reception but not with the 

 reliability and freedom from interference required of high grade repro- 

 duction. 



The effects which are actually realized in practice are indicated in 

 a more quantitative manner by the curves of Fig. 2 which are plotted 

 from some measurements made upon WEAF in New York and 

 WCAP in Washington, D. C. They were made at locations in the 

 New York and the Washington areas and at the intermediate points 



Station WEAF (610 KC) 



Station WCAP (640 KC) 



Distance- Miles 



Distance-Miles 



Fig. 2 — Results of a few measurements upon the reduction in field strength with 

 distance, including distances at which fading occurs 



indicated on the curves. The measurements at each of these points 

 are for one day only. They consisted in obtaining continuous graphic 

 records of signal intensity during twenty-minute intervals out of each 

 hour, one interval for each of the two stations. The period of time 



