STUDIES IN RADIO BROADCAST TRANSMISSION 



183 



Such barriers to wave travel, situaled within a short distance from 

 the source, seem, as we might exi)ect, to have a more extensive and 

 serious influence upon effective broadcast distribution than similar 

 obstructions at greater distances. 



It will be noticed that the obstruction falls very nearly upon the 

 direct line from the transmitter to the Stamford testing station. 

 This will also be evident later after an understanding of Fig. 29, 



150 

 140 

 130 



120 



no 



100 

 b^90 



2 70 ■== 



Si X 



40 

 30 

 20j 

 10 ' 







Zi° 25 27° 29° 



(Angle E of N from Transmitter) 

 31- 35° 35° 37° 39° 41° 43° 45° 47° 

 Across Manhattan 7 Wavelengtits from Station 



Fig. 29 — Cross-section of radio shadow caused by high building area 



wherein the position of the "Band Near Sound" represents also the 

 bearing of the Stamford station. The Riverhead station is not 

 directly in line with the major obstruction. 



In certain sectors of the field strength contour map for station 2XB 

 there appears to exist a kind of wavy displacement of the contour 

 lines forming a partial pattern of peaks and depressions side by side. 

 In general, this pattern must be differentiated from an ordinary 

 shadow area. A remarkable example of this sort of field distribu- 

 tion is shown in Fig. 1 which is one section of a field strength survey 

 made for station 2XB. These contours are based entirely upon 

 daytime measurements, and represent a condition which is stable 

 throughout the daylight period. Considerable difference in signal 

 level is apparent within short distances across the direction of wave 

 propagation. Two pronounced low signal channels extend ap- 



