118 BELL SYSTEM TECHNICAL JOURNAL 



sufficient strength to enable the received waves to stand well above the 

 level of the ever present interfering waves. 



3. Finally, the receiving set should pass with the necessary volume 

 all of the wave components required to reproduce the program signal 

 and should sharply exclude all others. 



The rapid apparatus development borne in by the vacuum tube 

 has brought the art to the point where it is now physically possible 

 to meet quite fully the terminal requirements. The apparatus de- 

 velopment, in fact, has outstripped our knowledge of the transmitting 

 medium itself, and we are now in the position of possessing apparatus 

 possibilities without knowing very definitely the limitations and re- 

 quirements placed upon their use by the intermediate link. Only 

 within the last few years have methods become available for measuring 

 radio transmission and thereby placing it upon a quantitative basis. 



Such measuring means have been applied to the study of radio 

 broadcast transmission from certain stations in New York City and 

 in Washington, D. C. The earlier results of this measurement work 

 have already been published. It is the purpose of the present paper 

 to present results of a systematic study which has been made of the 

 coverage which can be effected of the radio broadcast listeners of the 

 New York metropolitan area and in so doing to portray something 

 of the general systems requirements of radio broadcasting. 



The Character of Radio Broadcast Transmission 



The ideal law for broadcast distribution would be one whereby the 

 transmitted waves are propagated at constant strength over the zone 

 to be served and then fall abruptly to zero at the outer boundary. 

 All receivers within the area would be treated to signals of equal 

 strength and no interference would be caused in territories beyond. 



The kind of law which nature has actually given us involves a 

 rapid decadence in the strength of the waves as they are propagated 

 over the service area, and then, instead of a sharp cut-off, a persistence 

 to great distances at field strengths which, although often too low to 

 be generally useful, are sufficient to cause interference in other service 

 areas. 



This situation is illustrated in Fig. 1. The upper curve shows the 

 relation between intensity and distance; the lower portion, the inter- 

 pretation of this curve in terms of areas of reception. The attenuation 

 traced by the heavy line of the curve is that of the component of the 

 radiation which is propagated directly along the earth's surface. It is 

 this radiation which is ordinarily utilized for reliable broadcast recep- 

 tion. The shaded portions near the outer ends of this curve are 



