azimuth positions. The presentation shown could be a
ground map of an area of the earths 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
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