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BELL SYSTEM TECHNICAL JOURNAL 



Bn, the improvement in signal-to-noise ratio is 10 log N decibels referred 

 to one antenna. If, instead of receiver noise, static is the predomi- 

 nating noise, the signal power received is not significant but the same 

 improvement is realized for the general case in which the static is 

 distributed randomly among the N antennas.^- In that case the TV 

 signals are phased to add on a current basis while the N noise sources 



ANTENNA 1 



ANTENNA 2 

 R 



Es.Ea.En 



SINGE WAVE. SIMILAR ANT 

 ©ai - ®a2-' ^au- ©a 



AUDIO SIGNALS THEN IN PHASE 



EjOCNes 



EgocVFTea 

 E„ ccVNTe 



Ll = Vn^ 



En ^"^ e„ 



En 6n 



Fig. 33 — Simple signal-to-noise analysis of a system of N spaced antennas. Signal 

 currents are combined at audio frequency. 



add on a power basis. Analogous arguments apply to a series con- 

 nection of N antennas and result in the same improvement of 10 log N 

 decibels. 



^^ If static comes from all directions simultaneously, its distribution is random 

 among the ideal unit antennas discussed in Section II. This is deduced from calcula- 

 tions which show that gain (signal-to-noise ratio) is proportional to the length of 

 the system; i.e., to the number of unit antennas. The assumption of randomness 

 requires that the spacing of unit antennas having a certain angular discrimination 

 must be equal to or greater than the antenna length required to produce that dis- 

 crimination in the simple linear end-on type of unit antenna. 



That static is, on the average, distributed randomly among the rhombic antennas 

 of the experimental MUSA is shown by measurements described later in this section. 



