Radio Broadcast Coverage of City Areas ' 



By LLOYD ESPENSCHIED 



Synopsis: 1. Radio broadcasting involves a system of electrical dis- 

 tribution in which dependent relations exist between the transmitting 

 station, the transmitting medium and the receiving station. 



2. The attenuation and fading which attend the spreading out of broad- 

 cast waves are considered. The attenuation of overland transmission is 

 shown to be, on the whole, very high and to vary over a wide range depend- 

 ing upon the terrain which is traversed. The distance at which the fading 

 of signals occurs is found to be that at which the normal directly transmitted 

 waves have become greatly attenuated and to depend upon the terrain 

 traversed. 



3. A field strength contour map is given of the measured distribution 

 of waves broadcast by Station WEAF over the New York metropolitan 

 area. A rough correlation is given between measured field strengths and 

 the serviceability of the reception in yielding high grade reproduction. 

 The range of a station as estimated in terms of year-round reliability is 

 found to be relatively small. It becomes clear that the present radio 

 broadcasting art is upon too low a power level and that higher powered 

 stations are required if reliable year-round reception is to be had at dis- 

 tances as short even as 30 to 50 miles from the transmitting station. 



4. The question of the preferred location of a transmitting station 

 with respect to a city area is considered. It is shown that an antenna 

 located upon a tall building may radiate poorly at certain wave-lengths and 

 well at others. Surveys are presented of the distribution effected by an 

 experimental transmitting station located in each of several suburban points. 

 The locations are compared upon the basis of the "coverage" of receiving 

 sets which they effect. 



5. Finally, there is considered the relation which exists in respect to 

 interference between a plurality of broadcast transmitting stations operating 

 in the same service area. The importance of high selectivity in receiving 

 sets is emphasized and there is given the measured selectivity characteristics 

 for samples of a number of receiving sets. 



IT is well recognized that the elements which comprise an electrical 

 transmission system are required to function not simply as indi- 

 vidual pieces of apparatus, but as integral parts of a whole. In the 

 case of radio broadcasting, the absence of a common control of the 

 two ends makes this over-all "systems" aspect less apparent than it 

 is for wire systems.- Nevertheless a definite systems correlation is 

 required between the broadcast transmitting station and each of the 

 receivers served, as will be evident from the following: 



1. The transmitter should put into the transmitting medium, with- 

 out distortion and with the power called for by that medium, all of 

 the wave-band components required and no others. 



2. The transmitting medium should be capable of delivering to the 

 receiver an undistorted wave band, reliably and stably, and with 



1 Presented at the New York Regional Meeting of the A. I. E. E., New York, N. Y., 

 Nov. 11-12, 1926. 



" Some other examples of such a "systems" relationship are given in "Application 

 to Radio of Wire Transmission Engineering," published in the Proceedings of the 

 Institute of Radio Engineers, October, 1922. 



117 



