616 



DISPLAY SYSTEM DESIGN PROBLEMS 



B Scope 



C Scope 



Target 



90 270 



Target 



180" 

 Open ■ Center PPI 



Fig. 12-6 Intensity-Modulated Displays. 



modulate the electron beam, as shown in Fig. 12-6. The antenna azimuth 

 motion is measured to provide a horizontal deflection signal. 



The type C presentation is a plot of elevation angle on the ordinate 

 versus azimuth angle on the abscissa, as in Fig. 12-6. This presentation is 

 commonly employed for the display of angular tracking information such as 

 target angular position and computed steering error signals. It is not 

 normally used for target detection because all of the noise from one range 

 sweep piles up on one spot to compete with the signal return, if any, from 

 a given angular location. Thus, in comparison with the B scope, the 

 signal-to-noise ratio of the C scope is degraded by a factor of the order of 



6"/// degradation factor for C-scope presentation = (r/r)*' (12-1) 



where r = pulse length 



fr = repetition frequency 



K = (0.5 - 0.6) (see Sec. 3-5) 



In the PPI {plan position indicator), range and bearing are presented in 

 polar coordinates. The beam of the cathode ray tube starts from the center 

 of the screen when the transmitted pulse is generated and is swept radially 



