60 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1953 



* Includes three guard bands of 2,4 mc each to protect mobile and neighboring 

 services from mutual interference. 



Similarly, the guard bands of one subarea can be used for channels else- 

 where so all of the available 240 channels can be used. 



The examples given in Tables XIII and XIV represent the two 

 extreme conditions and the practical situation lies in between the two. 



By similar reasoning it is possible to estimate the number of usable 

 channels that can be obtained at frequencies around 450 mc. The num- 

 ber of usable channels shown in Table XV is for overlapping coverage 

 areas in a city or metropolitan area and the estimates given in Table 

 XVI are based on a uniform distribution over a state or other large sec- 

 tion of the country. 



Again, FM modulation with a bandwidth of ±8 kc and a system 

 frequency stability of 0.002 per cent are assumed. 



For a band^\'idth of 28 mc instead of 14 mc the number of usable 

 channels is doubled for the first four cases and is increased from 68 to 

 208 for the fifth case. The corresponding estimates for bandwidths less 

 than 14 mc are indefinite because of insufficient r.f. selectivity. 



conclusions 



The principal conclusions that result from Tables XIII, XIV, XV 

 and XVI, and from the preceding discussion can be summarized as fol- 



Table XVI — Usable Channels in State or Large Area 



AT 450 MC 



* Aflflumes adjacent channels are not assigned in same area. 



