Fire Control (Automatic Search)

azimuth positions. The presentation shown could be a ground map of an area of the earth’s surface showing several islands. The shape of the target appearing on the scope will be almost the actual shape of the target as viewed visually. If, however, the antenna were scanning above the horizon, an airborne target would be a very small bright spot, and the target shape would not be defined. Fire Control (Automatic Search) In the automatic search submode of fire control, information is displayed on both indicators. The PPI presents target range and azimuth information as before. Now, the B-scope also presents information that, if the system were operating in an aircraft, would be required to make a successful attack on an airborne target. This information is shown in figure 3-11. In figure 3-11, which is a normal B-scan search display, four items of interest are painted electrically on the face of the CRT. The first is the range sweep line, sometimes referred to as the B-trace. This time, however, the sweep is from the bottom of the scope to the top. Range on a B-scope is measured from the bottom of the scope to the top. The length of the trace then is equal to the range selected. If the 0- to 10,000-yard range is selected, the length of the range sweep line is 10,000 yards. The position of the sweep line on the face of the scope, as was the sweep line on the PPI, indicates the azimuth position of the antenna. The trace scans back and forth, following the antenna. You should notice that the scan line is not a single line, but is made up of several lines, causing it to become a 1/4-inch-wide scan line. This is called “jizzle,” and is the result of simulated antenna spin modulation. In an actual radar system, this is accomplished by nutation of the antenna feed horn or reflector dish. In the trainer a scan generator produces the effect of the antenna nutation, but the antenna is not actually nutated. Figure 3-12, view A, shows an antenna pattern that is simulated in the trainer. In view B of figure 3-12, a boxlike pattern is produced. This is accomplished by introducing a nod at the end of the scan. The second item on the scope is video (targets). As the antenna scans back and forth, any target within the range of the radar appears as a bright spot on the face of the CRT. The range of the target is indicated by its vertical distance from the bottom of the scope. The azimuth position of the target is indicated by the position of the target either to the left or to the right of Figure 3-11.-B-scan presentation in automatic search. the center. For example, if the target appears as shown in figure 3-11, its range is 7,500 yards (on the 10,000- yard range scale), and it is to the left of the attacking aircraft. Most radars installed in fighter-type aircraft also have an indication of the antenna tilt, which is used to indicate elevation position of the target relative to the attack aircraft. If the target were above the attacking aircraft, the antenna would have to be tilted up to receive a target echo. The amount of tilt can then be read from the indicator, and the pilot may steer the aircraft accordingly to intercept the target. The third item on the B-scope is the acquisition symbol. During automatic search, the acquisition symbol is relatively unimportant, but it is movable, and could be used to mark the area of target return. The symbol, as shown in figure 3-11, is made of two short vertical lines slightly separated. Position of the symbol in the vertical indicates range, and is controlled by the range circuits, which, in turn, are controlled by the hand control in an actual radar system. Movement of the hand control back or forward decreases or increases range voltage, which causes the acquisition marks to move in or out in range. The acquisition marks are also controllable in azimuth by movement of the hand control either to the left or to the right. Therefore, the acquisition marks may be positioned anywhere on the face of the scope. This is described in greater detail later. The fourth symbol on the face of the scope is the artificial horizon line. This symbol is a straight line with the center blanked out, and is positioned horizontally on the face of the indicator tube. The 3-12