THE RADAR RECEIVER 705 



tion is to amplify the video signal output of the second detector, together 

 with some other signals to be impressed on the cathode-ray tube. In this 

 lield the principles of design follow closely those developed for television 

 {)rior to the war. Band widths of the order of 1 mc to 5 mc are commonly 

 employed and output voltages ranging from 10 volts to 250 volts are re- 

 quired by the cathode-ray tube. Controllable nonlinear amplitude-gain 

 characteristics are occasionally included in these video circuits to enhance 

 the contrast or improve the apparent signal-to-noise performance. 



The display device uni\'ersally employed in modern military radar systems 

 is the cathode-ray tube. The electro-optical response characteristics of this 

 device may be chosen over quite wide limits to suit the specitic needs of a 

 particular system. In slow scanning systems, use of long time-decay optical 

 characteristics of the sensitive screen is found to be advantageous, while in 

 other cases of high-speed scanning, shorter persistence-type screens are 

 employed. Screen diameters commonly employed range from 2" to 12" 

 with a wide variety of color characteristics available to tit the detailed re- 

 quirement of the radar system. A variety of radar presentation forms are 

 employed to display most conveniently the received information for the 

 specitic application at hand. These display types differ i)rimarily in the 

 manner in which the radar tield coordinates are presented. The deflection 

 methods employed may be of an electrostatic or magnetic nature with com- 

 binations of each occasionally encountered. 



The sweep circuit components of the radar receiver generate the electrical 

 time wave forms necessary to display the received data properly. Here 

 again the television art has supplied a technical background for these 

 specialized electronic circuits. The great number of display types em- 

 ployed, requiring varied wave forms, has resulted in the development of a 

 myriad of specialized sweep circuits whose apparent complexity is the result 

 of varied combinations of elemental electronic circuits. 



The range and time-marker circuits are required to interpret the coor- 

 dinate data available to the receiver and to prepare this data for display 

 ill the desired form. Here again, television techniques have been employed 

 and enlarged upon as the radar systems became more comjilex. A large 

 number of specialized electronic circuit forms has resulted. 



The automatic frequency control (AFC) and automatic gain control 

 (A(1C) com])onents of a radar receiver have a function not unlike those ele- 

 ments found in most radio-communication systems. The automatic ad- 

 justments of the tuning and gain of the radar receiver has contributed greatly 

 to the successful employment of radar under practical military conditions 

 and have now become practically indispensable in the art. The circuit 

 designs follow, in general, the techniques i)reviously employed in radio 

 communications ihoutrh it will be <)l)ser\-ed that the character of the signal 



