and knowledge of the atmospheric propagation conditions. The two de- 

 vices arc: 



FTC — Fast time constant is a differentiating circuit which effectively 

 reduces the gain within the clutter area only. It is normally 

 used to limit scope clutter caused by reflections from at- 

 mospheric hydrometeors. 



STC — Sensitivity time control circuit reduces the gain of the re- 

 ceiver during the reception of short range signals. 



The effectiveness of these circuits in some situations is best illustrated by 

 comparison of the PPI scope presentation with and without application 

 of anticlutter devices as shown in figure 41. These photographs are from 

 a series of observations made on the 22-foot growler, subject of figure 39. 

 The top photograph shows the growler at 333°T; f>,000 yards and sea re- 

 turn from a 4-foot sea extending out to 5,000 yards. The gain and video 

 circuits were set for the maximum discernment of the target. Figure 41 

 (bottom) is a photograph of the PPI scope under the same conditions as 

 above except the STC circuit is used to decrease the near gain and thereby 

 obliterate the sea return. This was the optimum presentation that could 

 be obtained. It was found when working with growlers in sea return that 

 the FTC 1 circuit is valueless and on two occasions when weather obscured 

 the target (c.f. fig. 38) this device was ineffective. 



Results 



Intensive studies of the effectiveness of FTC and STC in discriminating 

 growlers in sea return have indicated that FTC is valueless and STC is 

 very effective if used with the proper combination of video and receiver 

 gain; however, on three different occasions it was not possible to detect 

 growlers in sea return although the radar was in peak condition and the 

 propagation conditions were near normal or only slightly subnormal. It 

 should be remembered that these anticlutter devices were designed to de- 

 crease the gain in a particular area on the scope and thereby reduce the 

 brilliant clutter and allow the strong persistent echo of a target to stand 

 out. The STC and FTC action appears to be useless unless the target echo 

 is stronger than the sea echoes and as has been demonstrated the basic 

 electrical properties of ice leave it as a poor reflector compared to sea 

 water. Of value to ice detection is the new type of logarithmic receiver 

 in which the effective gain is proportional to the logarithm of the signal 

 amplitude. This receiver characteristic provides higher gain for weak 

 signals and relatively lower gain for strong signals. However, the effective 

 use of this device or other controls including video and receiver gain re- 

 quires a skilled and experienced operator. It was only after many months 

 of constant radar surveillance that the writer was able to master the 

 intricacies of Lin-Log, STC and gain combinations which allowed the full 

 potentials of the system to be utilized. Evaluation of operators who have 



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