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BELL SYSTEM TECHNICAL JOURNAL 



and outermost minimum is due to the middle distance reflection with a 

 540-degree phase difference. It is unmistakable and definite. The 

 minima corresponding to phase differences of odd numbers of 180- 

 degree angles greater than three are not so clear cut. It is here that 

 the ground corrugations will have the greater destructive effect. 



10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 



MILES FROM TRANSMITTER 



Fig. 18 — Flight from transmitter. Altitude — 2500 feet; 

 wave-length — 4.3 meters, June 26, 1931. 



The method of calculation is more fully explained in Appendix I, 

 and the effect of a possible diffraction by Mt. Cushetunk in Appendix 

 II. In the 8000-foot curves ignition noise masked the deep outermost 

 minimum, and in the 1000-foot curve it is poorly defined, but it appears 

 well marked in the 5000- and 2500-foot curves, and is roughly 10 

 decibels below the theoretical value. This minimal depth corresponds 

 to a reflection coefficient of about 0.92 for this angle of incidence 

 (88.4 degrees); the theoretical reflection coeflicient is 0.8. 



General Observations 

 During these experiments no static was observed. It has since been 

 found by Mr. Jansky of the Laboratories that local summer thunder- 

 storms produce noticeable static interference and that such storms may 



