MOBILE RADIO TUANSMISSION 10G9 



150 mc region. This space is already allocated fully and permanently to 

 a variety of other services. In fact, this situation extends up to about 

 100 mc. The larger number of channels for these services apparently will 

 have to be found, therefore, above 400 mc. 



However, it is essential to know whether these higher frequencies 

 would be suitable for urban mobile telephone service, or whether there 

 exists an upper limit to the suitable frequencies. In order to answer these 

 questions, a series of tests has been made to compare the adequacy of 

 coverage that could be pro\'ided at several representative higher frequen- 

 cies. These tests were conducted in and around New York City. This 

 location is considered to be typical of the larger metropolitan areas. 



THE PROBLEM OF EVALUATION 



It became apparent early in the tests that it would neither be practical 

 nor accurate to compare service results for the different frequencies by 

 the method of determining the coverage at the various frequencies, and 

 then comparing these. This would have requiretl, among other things, 

 that "coverage" be defined precisely and then measured accurately in 

 order to determine the differences with the desired accuracy. 



Instead, it was recognized that commercial coverage is at present 

 considered to extend into areas wherein a small percentage of the loca- 

 tions wiU have less than commercial grade of transmission. This might 

 be ten per cent, for example. It was further recognized that, while there 

 existed a trend of performance with frequenc}^, comparative tests at any 

 one location showed variations from that trend. Thus, even if trans- 

 mitter powers were adjusted so as to offset the transmission effects of 

 that trend, performance at any location would not be equal at all fre- 

 quencies. But while one frequency might give relatively poor trans- 

 mission in one location, it might give good transmission at another 

 location, etc. Thus, while the locations of poor transmission were found 

 to be different at the various frequencies, the number of such locations 

 would be the same at all frequencies, provided the trend had been offset 

 by adjustment of transmitter power. 



Vie^^^ng the problem in this way, it was sufficient to test at enough 

 locations in representative territory to establish this trend in a statistical 

 manner. 



Other problems in e\'aluating differences in suitability of different 

 frequencies lay in how to take into account differences in practical 

 antenna gains and differences in frequency stability. These will be dis- 

 cussed in the next sections. 



