THE RADAR RECEIVER 757 



A-type indicator which was employed for certain conveniences in operation 

 and maintenance of the equipment. This circuit design includes a main 

 video amplifier for the ground plan indication and a separate amplifier for 

 the A-type display, both of which are of the negative feedback type. The 

 limiting amplifier is included as the second stage with negative d-c restora- 

 tion included in this grid circuit and diode d-c restoration at the grid of the 

 last stage. To provide sutlficient output signal level with the wide video 

 band width required it was necessary to employ two 6A(j7 tubes in parallel 

 in the final output stage of the main video amplifier. The local indicator is 

 fed from the j)late circuit while the remote navigator's display is fed by 

 means of a low impedance coaxial transmission line. The video gain control 

 is essentially an adjustment of the video amplitude limiting level, the actual 

 signal amplitude being previously adjusted by the IF amplifier gain control. 

 The over-all gain of the main video amplifier is approximately 32 db with a 

 band width of approximately 5 mc. The over-all gain of the A-type display 

 amplifier circuit is approximately 43 db with a useful band width of ap- 

 proximately 6 mc. 



2.4 The Radar Indicator 



The radar indicator assumes a position of extreme importance in the 

 components of the radar receiver. Here with a few specific exceptions all 

 of the electrical information which has been obtained regarding the area 

 under observation is finally correlated and converted into an optical display 

 for use by the radar observer. In the discussion thus far, only the received 

 radar microwave signal properly selected, amplified, and finally converted 

 to the video form has been discussed in detail. The preparation of the addi- 

 tional coordinate and reference data necessary to properly present the com- 

 plete scene is reviewed in the following sections. In this section the charac- 

 teristics of the presentation will be reviewed from the standpoint of the 

 requirements imposed by the various radar applications. The electro- 

 optical characteristics of the display device are also discussed. 



2.41 Classification of Radar Display Types 



The number and types of display methods which have been developed for 

 military radar systems during World War II are the result of the varied 

 specific applications to which radar has been subjected. These types of 

 displays are in general related directly to the functional classification of 

 military radar systems previously discussed. It is of interest to consider 

 at this time the various types of indicators which have become common in 

 the radar field. Figure 37 illustrates the basic characteristics of the most 

 important types of radar presentations. 



Basically the three coordinates which determine the position of the target 



