ULTRA-SHORT-WAVE PROPAGATION 267 



data may be represented also by an inverse-square-of-distance curve. 

 By comparison with Fig. 2 no differences that can be attributed to the 

 change in position of the fixed terminal nor the direction of transmission 

 is evident. There is a small difference in the separation between the 

 mean curves and the "level terrain" curves, but in both instances the 

 mean curve lies very close to the level terrain curve (not shown) that 

 would result from measuring the antenna height of the fixed terminal 

 from the average roof level instead of from the ground. 



Most of the nearby points were taken in the park system. They 

 indicate that it is not more difficult to transmit through wooded areas 

 than through built-up sections. 



A field strength contour map illustrating the results obtained with 

 the receiver fixed at Seaverns Street is shown in Fig. 11. The disturb- 

 ing efTect of hills is illustrated at several points on the map. There was 

 a reduction of field when the transmitter was behind either Bussey 

 Hill at A on the map or Green Hill at B, while the field was higher 

 when the transmitter was between them. There was a rather deep 

 minimum when the transmitter was immediately behind Parker Hill 

 at C to the north, but half a mile farther away there was no noticeable 

 efifect. 



Effect of Obstacles 



In the course of the measurements some qualitative observations 

 were made which will be summarized in this section. It was noticed 

 in particular that when the receiver passed underneath an intersection 

 of overhead trolley wires, the field was somewhat reduced. An 

 example of this effect was observed at the intersection of Massa- 

 chusetts and Huntington Avenues where the reduction was 15 db. 

 At this point the maze of overhead trolley and support wires apparently 

 constituted a fairly efificient screen for these waves. Observations 

 made during the tests showed that sometimes the field was con- 

 siderably reduced on the far side of hills as has been brought out by 

 the contour maps. A large reduction in field strength resulted upon 

 going behind a low hill on Saratoga Street on Breeds Island. The 

 most striking example of this efifect occurred with the measuring set 

 at Seaverns Street and the mobile transmitter being driven from 

 Huntington Avenue onto South Huntington Avenue (C of Fig. 11). 

 Soon after rounding the corner at the foot of Parker Hill, which is 200 

 feet high, the average field dropped about 15 db. 



The field was 20 db lower under Funeral Bridge than on either 

 side of it. This is a stone and earth bridge appearing as a short 

 tunnel to the road beneath it. The field was usually reduced upon 

 passing underneath bridges of this general type of construction. 



