12-3] TYPES OF DISPLAYS 615 



has enough gain; thus the signal drive limitation is not in the tube. This is 

 not true of intensity-modulated displays. 



A modification of the type A scope, the type J, increases the length of the 

 time base (Fig. 12-5). All the disadvantages and advantages of the type A 

 presentation exist, with the additional advantage that a longer time base 

 can be displayed for the same diameter of tube. There are also additional 

 disadvantages in that system circuitry complexity is increased and a 

 special cathode ray tube is required.^ 



Other modifications of the type A are the types K and L displays. These 

 presentations are used to obtain directional information of a target when 

 two antennas or a sequential antenna lobing system is used. The antenna 

 beam patterns are offset so as to make a small angle between the two 

 patterns. The on target position is obviously that position which is 

 equally illuminated by both antenna beams. This would exist only when 

 the target is along the centerline of the sequentially lobed antenna (or 

 along the centerline between two separate antennas). 



As shown in Fig. 12-5, the type L scope presents the target information 

 from each beam on the cathode ray tube in a back-to-back manner so that 

 correction can be made to equalize the video signals and thereby align the 

 antenna system to target. In the mechanization of sequential lobing and 

 antenna switching, alternating pulses are used for the right and left antenna 

 beams. The display is so arranged that the signal appearing on each side 

 of the display is associated with the proper antenna beam. The antenna 

 motion necessary to align the antenna and target is then evident from the 

 scope. 



The type K scope is a variation of the type L scope. Instead of a back-to- 

 back display, a side-by-side display is used. The sequence of antenna lobe 

 switching is similar to the L scope. This display is shown in Fig. 12-5. 

 Neither the type L nor type Kscopes are used much in airborne installations, 

 except for programed flights at low levels. 



Intensity-Modulated Displays. In order to give additional in- 

 formation on the two-dimensional cathode ray tube, grid or intensity 

 modulation is provided in the types B, C, and PPI scopes; thus the two 

 dimensions of the CRT face are available to display pertinent target 

 information other than signal-return intensity (for example, range, azimuth, 

 elevation, height). 



The type B presentation is a form of intensity-modulated display which 

 is commonly used in airborne radar search displays. The indicator presents 

 a cartesian plot of antenna azimuth position along the horizontal axis and 

 range on the vertical axis. The video information is used to intensity- 



2L. N. Ridenour, Radar System Engineering, pp. 166-167, McGraw-Hill Book Co., Inc., 

 New York, 1947. 



