CALIHKATION \XI> TKSTINC 



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TARGET- INCOMING MEDIUM BOMBER 



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Figure 77. Test flight data from a calibrated receiver. 



is 2 and the percentage error is probably greater than 

 on the reading at 68.5 miles. The location of points 

 on the lobe cannot be read with accuracy from Figure 

 76 at S/N = 1 since this is threshold data which 

 may be in considerable error. 



To determine the maximum free space range F, 

 the lengths of the lobes obtained from the test data 

 may be listed along with the site factors from equa- 

 tion (99) or equation (107). A value of F is then 

 selected which will most nearly fit the test data. 

 Variations in performance of the equipment affects 

 the lobe lengths in proportion. Variations from the 

 standard atmosphere assumed will shift the position 

 of the lobes, particularly at low altitudes. 



Where better accuracy is desired or the receiver is 

 nonlinear, the calibrated receiver method is required. 

 Such data are recorded as gain voltage, range, and 

 time. For each gain voltage, the equivalent receiver 

 input voltage is read from a calibration curve such 

 as Figure 74. The equivalent value of the noise 

 voltage of this set is 30 ixv. Dividing the equivalent 

 receiver signal voltages by 30 gives the S/N ratio 

 which is plotted against range in Figure 77. The 

 lobes are identified by reference to a lobe angle 



diagram. The extrapolated lobe lengths may be listed 

 as follows : 



The 20,000-ft data were taken last and indicate the 

 effect of certain equipment adjustments. The ability 

 to maintain this performance is one of the questions 

 to be considered in arriving at a weighted average 

 value of lobe lengths. Comparison of these lobe 

 lengths with the computed lobe factors will indicate 

 a fair value to be used for the free space maximum 

 range. 



Until suitable instruments are provided for 

 measuring set performance the conduct of successful 

 tests will continue to be a challenge to the ingenuity 

 and diligence of field personnel. However, with a 

 careful analysis of the propagation characteristics of 

 a given site and radar equipment and a well-conducted 

 test with inadequate instrumentation minimized by 

 determined improvisation, it is still practical to 

 obtain a reliable solution to the coverage problem. 



