146 BELL SYSTEM TECHNICAL JOURNAL 



careful observations demonstrated that there were points relatively 

 near New York City where quality distortion from several broad- 

 casting stations in the city was marked at night and in at least one 

 case was detectable even in daytime. When station 2XB the Bell 

 Telephone Laboratories' experimental station at 463 West Street, 

 New York City, was used to transmit test signals, it was found that 

 quality distortion could be observed in northern Westchester county 

 and in southern Connecticut at distances of about 30 to 50 miles from 

 the transmitter. Fading was also pronounced and it was noted as a 

 significant fact that distortion was always accompanied by some fading 

 although the reverse was not consistently true. In the course of these 

 trials it was noticed that at a particular point near New Canaan, 

 Connecticut, signals from 2XB were much weaker and more dis- 

 torted than signals from 2XY, the experimental station of the Amer- 

 ican Telephone and Telegraph Company at 24 Walker Street, New 

 York, even though the transmitter at 2XB was about ten times more 

 powerful. Daylight field strength measurements at this point showed 

 that the field strength of 2XB was only one-third that of 2XY. This 

 led to the rather startling conclusion that there is a ratio of 100 to 1 

 in the power efficiency of transmission to that particular receiving 

 point from these two transmitting stations in New York which are 

 only about one mile apart. 



In order to throw some light on this state of affairs a field strength 

 survey was made by G. D. Gillett which resulted in the field strength 

 contour map ^ here reproduced in Fig. 1. The contours on this map 

 show that there is a series of long nearly parallel hills and valleys of 

 field strength which, extrapolated, would converge in lower Man- 

 hattan and which extend out to the northeast as far as it was thought 

 worth while to follow them. There has occurred to us no better 

 explanation of this hitherto uncharted form of field strength distribu- 

 tion than that it is a gigantic wave interference pattern. A detailed 

 discussion of this theory is given in another section of this paper. 



The fixed pattern shown by Fig. 1 is definitely present only in the 

 daytime but that it is fixed is attested by the fact that a second survey 

 made about a year later checks with the original one quite closely. 

 At night fading is pronounced in the area covered by the pattern and it 

 is apparent that some other factors must enter. As a result of an 

 endeavor to check up the pattern at night it was discovered that 



1 This map was prepared by Mr. Gillett using the methods discussed in a paper 

 "Distribution of Radio Waves from Broadcasting Stations Over City Districts," 

 by Ralph Bown and G. D. Gillett, I. R. ¥.. Proc, Vol. 12, No. 4, p. 395— August, 

 1924. 



