A MULTIPLE UNIT STEERABLE ANTENNA 



409 



From the point of view of the interfering effect upon speech it is not 

 clear which method of averaging is more significant. This matter is 

 probably related too closely to the distortion which incidentally 

 accompanies the noise peaks to be considered alone. 



In the light of the discussion presented in the preceding pages it 

 appears that the signal-to-noise improvement of the experimental 

 MUSA can be expressed as 8 ± 1 decibels. 



MUSA 



NO. t ANTENNA 



m 



Z Q -5 

 7, ? -10 



f- u +5 



2 r, 



o z 



z - 



Fig. 41 — Sample of signal and noise variations occurring in MUSA tests. The 

 arrows indicate noise levels beyond the scale of the meter. This record was obtained 

 five minutes before that in Fig. 40. 



Square-Law Detectors 



In the discussion of the signal-to-noise measurements it was stated 

 that the measured improvements would have been higher had square- 

 law audio detectors been used instead of linear rectifiers. For the two- 

 bundle MUSA measurements one decibel was allowed for this and for 

 the three-antenna diversity measurements at Netcong 0.5 decibel was 

 allowed. These figures are based upon tests to be described in the 

 following paragraphs. First, however, an analysis will be made of the 

 effect upon the signal-to-noise ratio of various types of detectors in a 

 MUSA system. Figure 42 is a schematic representation of the system to 

 be analyzed, comprising K branches. The K signal generators esA, Csb, 

 • • • esK represent the various wave bundles as received by the steerable 

 branches. The noise generators enA, SnB, • • • CnK are equal in ampli- 

 tude but random in phase. The detectors are generalized to the 

 extent that the audio output is proportional to the u power of the 

 input. 



Assuming that Bs^^ e„ the audio outputs are proportional to e"sA, 

 B'^sB, • • • e'^sK- The noise outputs are then proportional to e„4esA"~\ 

 enBesB'^~^, • • • «nit^sK"~^ siucc the signal-to-noise ratio in each branch 

 must be independent of u. Assuming the signals to be delay equalized, 



