620 DISPLAY SYSTEM DESIGN PROBLEMS 



3. Bandwidth 



4. Number of amplitude levels 



5. Linearity, accuracy, and resolution of the reference signals 



The total number of matrix elements provides a measure of the total 

 number of "chunks"^ of information that the display system may have to 

 handle. This number is instrumental in establishing the required size of 

 the indicator. 



The number of matrix dimensions and the number of elements per 

 dimension have a strong influence on the type of display to be used. As was 

 indicated in Paragraph 12-3, the display device is usually two-dimensional. 

 Additional information dimensions are supplied by coding the two-dimen- 

 sional symbols or by providing additional displays. Regardless of the means 

 employed, the extra dimensions are supplied at a considerable price in 

 complexity and operator interpretability. This price tends to increase with 

 the number of separate elements in each of the extra dimensions. Thus 

 there is a strong premium on using the indicator dimensions for those 

 information dimensions which have the largest number of elements. The 

 extensive use of the B scope for AI radars illustrates this principle. Such a 

 radar may have 100 range elements, 30 azimuth angle elements, and 2-3 

 elevation angle elements. Customarily, range and azimuth are displayed 

 on the indicator dimensions, while a separate strobe is used to indicate 

 elevation. The bandwidth of the input information is governed by the 

 video bandwidth of the radar receiver (or by the devices placed between 

 the video amplifier and the indicator). The number of amplitude levels is 

 governed by the S /N ratio. For example, a maximum S /N ratio of 20 db 

 implies that there are ten distinguishable voltage levels in the incoming 

 signal. 



Closely related to questions of bandwidth and number of levels is the 

 character of the video itself. Three types of video may be used as an input 

 to the display system: (1) raw video, (2) processed video, and (3) artificial 

 video. 



Raw video is obtained directly from the radar video amplifier output. 

 This signal contains the target information and internally and externally 

 generated noise. The presence of noise complicates the indicator design 

 problem particularly in the detection phase where operation of very low 

 S /N ratios is required to obtain maximum performance from the radar. 

 This was indicated in Paragraph 12-3 in the discussion of the use of C scopes 

 for detection. 



In some cases, the raw video may be processed in some fashion before 

 display. Typical processes are (1) pulse stretch (see Paragraph 5-6), 



■"A c/iunk of information may be defined as a separate message. For example, the range, 

 azimuth, elevation, velocity, and amplitude of a single target is a chunk of information. 



