AMPLITUDE, ANGLE, AND RANGE NOISE 



201 



frequency. The propeller modulation occurs at the blade frequency (engine 

 rps X number of propeller blades), so the fundamental modulation fre- 

 quency should be the same for all radar frequencies. This was seen to be 

 the case for the F-51, as illustrated in Fig. 4-19.^'' 



It/) 



I I I I I r 



2 4 6 8 10 15 20 25 35 45 60 

 f(cps) 



B - 45 RUN 10 1250 Mc/sec 

 RANGE 13,600 YD 

 AZIMUTH 96°20' - 98°42' 

 ELEVATION 6°56' - 6°55' 



2 4 6 8 10 15 20 25 



f(cps) 



35 45 



B - 45 RUN 10 2810 Mc/sec 

 RANGE 13,300 YD 

 AZIMUTH 91° -94° 

 ELEVATION 6° 55' 



2 4 6 8 10 



35 45 60 



B- 45 RUN 10 9380 Mc/sec 

 RANGE 13,600 YD 

 AZIMUTH 96° 20' - 98° 42' 

 ELEVATION 6° 56' - 6° 55' 



Fig. 4-24 Spectrum of Amplitude Noise of B-45. 



For a jet aircraft, the mechanical vibrations of the salient reflection 

 surfaces would be expected to be of high frequency and noiselike in nature 



'■'Because the radar samples the instantaneous radar area of the target at discrete intervals 

 r times per second (r = the pulse repetition frequency), a frequency of s cps in the spectrum 

 could result from beats between the actual frequency and the repetition frequency. Hence 

 the actual frequency of the target radar area spectrum may be any value given by «r ± s, 

 where n is an integer (including 0). For the F-51, the observed propeller modulation frequency 

 was found to correspond to w = 7 or 8. 



