12-5] THE CATHODE RAY TUBE 621 



(2) pulse length discrimination, (3) integration, (4) amplitude limiting, 

 (5) noise clipping, (6) logarithmic amplifications. Each of these processes 

 may affect the signal-to-noise ratio, the bandwidth, and the size and shape 

 of the video pulse information. The methods outlined in Chapter 5 must 

 be employed to form an analytical definition of the display system input. 

 Certain types of radar systems — notably doppler systems — may 

 require the generation of artificial video — i.e., video that is generated 

 to represent signals already detected. In these applications, the concept 

 of S /N ratio no longer has meaning since the artificial signals are generated 

 at an arbitrarily high S /N ratio to ensure that only signal information 

 appears on the display. With respect to the requirements imposed on the 

 indicating device, this type of signal poses the same sort of problems as 

 the display of instrument readings and data link information. 



Computed Signals. In many important applications the radar video 

 information is processed automatically and used in conjunction with other 

 information to compute various quantities which are then displayed to the 

 operator. The tracking phase of the interceptor fire-control problem 

 represents such a case. The signal sent to the display will be affected by 

 the S /N ratio of the radar information as modified by the processes of 

 computation and smoothing. For example, range and angle tracking noise 

 will result in jitter of the computed steering indication. Filtering can cause 

 a time delay detrimental to steering loop stability. 



In addition to the noise and time delay, it is important to define the 

 following other properties of computed signal inputs: 



1. Total amplitude range 3. Linearity and resolution 



2. Bandwidth 4. Number of dimensions 



For the display of information derived from sources other than radar, 

 similar comments apply. 



12-5 THE CATHODE RAY TUBE 



The general elements of the display system problem have been discussed 

 and some of the more common types of displays have been illustrated. 

 Now we shall turn our attention to the display device itself to ascertain the 

 characteristics that are most important to the solution of the display 

 problem. 



To provide a reference for this discussion, the important general charac- 

 teristics of display devices will be illustrated by the specific performance 

 characteristics of cathode ray tubes. Despite the development of many 

 more esoteric display devices, the cathode ray tube is still the most generally 

 useful radar display device; moreover, an understanding of the operation 



