UL TRA -SHOR T- WA VE PROP A GA TION 



263 



„■ '^ 50 



0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 



RELATIVE DISTANCE ALONG ROUTE IN MILES 



Fig. 6 — Portion of record showing the large field strength variations as recorded 

 while driving through the business district of Boston at a distance of about 1.5 miles 

 from the transmitter. 



0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 



RELATIVE DISTANCE ALONG ROUTE IN MILES 



Fig. 7 — Portion of record showing the small variations of field strength while 

 driving through the residential section of Boston at a distance of about 5 miles from 

 the transmitter. 



taken at a distance of five miles (near B in Fig. 8). The change in the 

 magnitude of the variations might have resulted from the fact that 

 all of the data for the greater distances were taken in residential 

 districts with correspondingly lower heights and densities of buildings. 

 An idea of the variations to be expected from the inverse-square-of- 

 distance relationship is shown by the contour map of Fig. 8. The data 

 already presented will give an idea of the impossibility of showing 

 much detail in such a map. Likewise it would be an almost endless 

 job to make measurements on every street in a city of this size. While 

 data were obtained within reasonable intervals over the area for which 

 solid contours are drawn (continuous field strength records taken 

 over 143 miles of street are represented by this figure), another set of 

 data might result in a somewhat different looking map. The broken 

 contours are not based upon field strength measurements, but are 

 merely a plausible way of joining the solid contours to aid the eye of 

 the reader. The two 20 db contours in the lower part of the figure 

 have not been joined because of insufficient data. The low field 

 strengths along the Neponset River may be a result of local conditions 

 and possibly the 20 db contours should be continued to the right along 



