12-10] 



SPECIAL DISPLAYS 



673 



Deflection Yoke 



Electron Lens Aperture 



Number 2 



Cathode 



Matrix Selection Plates 



Fig. 12-48 Basic Optics of the APSEL Tube. 



to the proper point on the screen. This principle is used in the APSEL 

 version of the Charactron. The total length required is less than with the 

 first method. 



12-10 SPECIAL DISPLAYS 



Special indicators have been devised to optimize information display in 

 particular tactical situations. 



Terrain Avoidance. Attack against ground objects may be conducted 

 at a low altitude. Avoidance of high obstacles as well as detection of targets 

 becomes the concern of the radar operator and pilot in such a tactical 

 situation. A radar system designed for terrain avoidance operation requires 

 high resolution, a short frame time, and an easily interpreted alarm display. 

 High resolution is necessary to recognize the terrain objects in the search 

 sector. A short frame time is necessary to up-date the information quickly 

 to allow maximum aircraft operation decision time. Both resolution and 

 frame time are limited by other units of the radar, such as the antenna, 

 rather than the indicator. 



Typical indicator configurations for terrain avoidance make use of either 

 B, C, or sector-scan PPI presentations. Such displays give a maplike 

 picture of the terrain obstacles which must be avoided. The ideal display 

 should show range as well as angular position. The B, C, or sector-scan 

 PPI are, therefore, compromise displays which leave out some information 

 which is useful to the operator. In the C scope. Fig. 12-49, a profile of the 

 terrain can be visualized from the display and therefore the pilot can 

 adequately judge the aircraft maneuver necessary to evade the obstacle; 

 however, he has no knowledge of the terrain behind the displayed terrain, 

 and therefore idealized flying along the valleys between terrain obstacles is 

 difficult. In the B (or sector-scan PPI), as shown In Fig. 12-49, a better 



