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BELL SYSTEM TECHNICAL JOURNAL 



surface ripples to represent the waves foreign to broadcasting which 

 cause interference. Sight should not be lost, however, of the fact 

 that the contour lines of Fig. 4 represent a two-dimensional section of 



Fig. 4 — Field strength contour map of distribution over the New York metro- 

 politan area, effected by Station WEAF. 5 kilowatts in antenna, frequency 610 

 kilocycles, wave-length 492 meters. 



a three-dimensional phenomenon. One should picture the contours 

 as the intersections of the earth's surface with three-dimensional 

 surfaces. 



The fact previously referred to that the waves transmitted into 

 Westchester County experience high attenuation is shown by the 

 shape of the contour lines. The irregularity of the lines appears to 

 be due to a splitting of the directly transmitted wave by the high 

 building area and the filling in from the sides of wave energy trans- 

 mitted along the two sides of the peninsula. Although the conditions 

 in Westchester are quite stable during the daytime, they become 

 unstable at night due, apparently, to the addition of the indirectly 

 transmitted component reflected from above. An experimental study 

 of this interference situation disclosed the fact that the bad quality 



