266 



BELL SYSTEM TECHNICAL JOURNAL 



The greatest difficulty encountered in attempting to apply the 

 results of these experiments to the pre-determination of the field to be 

 expected for transmission in other cities would be the interpretation 

 of the method of assigning values to the heights in equation (5). 

 While sufficient data are not available to establish an empirical re- 

 lation, for a first estimation it seems reasonable that if the height of 

 the fixed antenna were measured from the general roof level of the 

 surrounding buildings and the height of the mobile antenna were 

 measured from the street level, the resulting field strengths would lie 

 within the range of expected values. ^^ 



Field Strength Measurements 

 Receiver at a Fixed Location 

 The field strength data obtained with the receiver at Seaverns 

 Street and the transmitter in the truck are shown in Fig. 10. These 



80 

 "n 75 



70 

 65 

 60 

 55 

 50 

 45 

 40 

 35 

 30 

 25 

 20 

 15 



O 

 ^< 



UuJ 



:;< 



^^ 



o> 

 tn < 

 <5 



02 

 .2< 



Q5 



S5 



0.15 0.2 



0.3 0.4 0.6 0.8 1.0 1.6 2.0 30 4.0 60 80 10 



DISTANCE FROM TRANSMITTER TO RECEIVER IN MILES 



Fig. 10 — Mass plot of field intensities measured with the transmitter at various 

 distances about the Seaverns Street location. The open circles represent fields 

 averaged over one-tenth mile intervals while the solid circles represent averages over 

 one-half mile intervals. 



" This should not be expected to be true for antennas close to the roof, since the 

 field-strength obviously would not go to zero when the antenna height goes through 

 the roof level. Extreme caution should be used in applying these results to cities 

 in which the density and uniformity of buildings differ from those of Boston. When 

 the topography departs greatly from that of level terrain, it would be difficult to 

 infer the transmission conditions from the data here presented. 



