ULTRA-SHORT-WAVE PROPAGATION 255 



mediate frequency attenuator.* This receiving equipment was cali- 

 brated in absolute units by a method described in the appendix. 

 A mechanism for recording the field strength was attached to the 

 measuring set: this consisted of a roll of paper that could be driven 

 either by clock-work or by the rear wheels of the truck. The position 

 of the recording pen was controlled by the setting of a manually 

 operated variable attenuator. Samples of the type of record obtained 



are shown in Figs. 6 and 7. 



Locations 



The radiator for the fixed transmitter was supported by a fifty-foot 

 pole above the roof of a seven-story building at the corner of Berkeley 

 and Stuart Streets in the business section of Boston. The building is 

 about 90 feet high, making the center of the antenna about 130 feet 

 above the ground. Thus, the antenna was higher than most of the 

 buildings of the city though it was lower than a few buildings nearby. 



The antenna for the fixed receiver was supported by a 20-foot pole 

 from the middle of the highest ridge of a gabled building making the 

 center of the antenna about 80 feet above the street level. This 

 building is located on the side of a slight slope in a fairly heavily 

 wooded territory, on Seaverns Street near Center Street. 



Field Strength Measurements 



Transmitter at a Fixed Location 

 With a current of one ampere in the half-wave antenna ^ above the 

 building at Berkeley and Stuart Streets and with the receiver in the 

 truck, field strength measurements were made along various routes 

 throughout Boston. These data have been averaged by one-tenth- 

 mile intervals when the average radial distance was less than two 

 miles and by half-mile intervals for greater average distances. A plot 

 of these data is shown in Fig. 2. The points lie approximately on an 

 inverse-square-of-distance line with deviations ranging up to about 

 ± 10 db. An effort has been made to separate the points taken in 

 the high building area. These points (shown as open circles) lie 

 somewhat below the others with a few particularly low field strengths. 

 The lowest field strengths of the business district were measured along 

 the shore near Charles River Dam and near State Street on Atlantic 

 Avenue. The field strengths in the business district would be expected 

 to be lower because of the presence of the high buildings. The lower 



' The set was similar to that described by Friis and Bruce, Proc. I. R. E., Vol. 14, 

 pp. 507-519, August, 1926. 



* Since the antenna was in free space in so far as radiation resistance is concerned, 

 this corresponds to a radiated power of 73 watts. 



