TEE RADAR RECEIVER 



763 



lar lines originally established by prewar television. Two general types of 

 cathode-ray tubes have been commonly employed in the military radar 

 program, electrostatic and magnetic, these classifications being indicative of 

 the deflection and focussing method employed. 



Electrostatic Deflection Type 



A typical form of electrostatic-type of cathode-ray tube suitable for radar 

 indicator purposes is shown in Fig. 38. In this tube type the electrons 

 emitted from an indirectly heated cathode surface are initially formed into 

 a beam by passage through an aperture which serves as a beam density or 

 ultimate brightness control element. Following this, the electrons proceed 

 through another aperture which is maintained at a positive potential with 

 respect to the cathode. This first anode together with the following second 

 anode forms an electron lens system which focuses the beam on the fluores- 



ELECTRON 

 GUN V, 



I 

 CATHODE _[ 



HEATER 



CONTROL 

 GRID 



SECOND 

 ANODE 



DEFLECTION PLATES: 

 VERTICAL HORIZONTAL 



FLUORESCENT 

 SCREEN 





ji y 



^ FIRST 

 FOCUSING 

 ANODE 



HIGH -VOLTAGE ,^ 

 AUXILIARY ANODE 



II j i ANOUb ' I 



Fig. 38. — Schematic diagram of an electrostatic type cathode-ray tube. 



cent screen surface. The relative potentials of these elements serve to 

 enable focussing of the beam by electrical means. The deflection of the 

 beam for scanning purposes is here accomplished by the introduction of an 

 electric field formed by the application of potential across the deflection 

 plates shown. Two pairs of plates enable separate horizontal and vertical 

 deflection to be employed. The plates are formed as shown to enable ob- 

 taining the maximum deflection per unit of electrical potential applied with- 

 out interference with the beam under large deflection conditions. The 

 high-voltage auxiliary anode is provided in certain tube types to further 

 accelerate the beam after deflection without an appreciable reduction of 

 deflection sensitivity and results in an image of increased brightness. 



To realize optimum performance of an electrostatic-type cathode-ray 

 tube several precautions must be observed. Serious defocussing of the beam 

 as it is deflected will result if the average potential of the pair of deflection, 

 plates is allowed to vary substantially from the value present at the second 

 anode. To minimize this effect, balanced sweep deflection amplifiers are 



