600 BELL SYSTEM TECHNICAL JOURNAL 



It seems especially questionable whether such synchronism is neces- 

 sary since tests in this area have shown that the use of a simple direc- 

 tive antenna capable of moderate discrimination against the weaker 

 of the stations at the point in question is sufficient to render the recep- 

 tion at least comparable to that from either station alone. A loop 

 antenna grounded at one side instead of the center was found to be 

 very effective. 



Population studies made in connection with the field surveys show 

 clearly how marked is the improvement in the service rendered by these 

 particular stations under simultaneous operation as compared with op- 

 eration on a shared time basis. On a shared time basis a population of 

 approximately 1,000,000 received adequate service from these stations 

 but half the time, the value of which was greatly impaired by its inter- 

 mittent character. With simultaneous operation the service area of 

 each station receives full time service. No accurate estimate can be 

 made of the number of people in the middle area, and outside the nor- 

 mal service range of either station alone, whose reception has been 

 further impaired by simultaneous operation. The importance of this 

 effect can, however, be estimated from the fact that but 60 complaints 

 of impaired reception were received by these stations in the first 35 

 days of simultaneous operation during the regular hours and that the 

 total for the first year is less than one hundred. 



The marked increase in the service rendered by these stations 

 through simultaneous operation is an indication of the possibilities of 

 the improved service that can be made available to urban areas by the 

 use of isochronized transmitters for the broadcasting of a common pro- 

 gram. Although it is probable that the high powered station on a 

 cleared channel will remain the best means of affording a high-grade 

 service to a metropolitan area while also rendering an acceptable serv- 

 ice to large rural areas, common frequency broadcasting now appears 

 to offer a definitely useful means by which to provide an improved 

 coverage to a number of noncontiguous communities. 



In conclusion, the author wishes to acknowledge his especial in- 

 debtedness to the following members of Bell Telephone Laboratories: 

 to Mr. G. R. Stiblitz for the development of the probability curves, and 

 to Mr. C. B. Aiken and Mr. R. J. Jones for their preparation of the 

 distortion curves as a part of their general mathematical study of the 

 problem. 



