marks bracket and move with the B-trace, and the
antenna is controllable in azimuth. All symbols that
were present in automatic search, including the
artificial horizon, are present in manual search. The
horizon line still functions to indicate aircraft attitude.
It should also be reasonable to expect to see no targets
other than the ones that appear on the range sweep
line, since the antenna is no longer scanning.
Fire Control (Lock on)
The lock on mode is a momentary mode of
operation between manual track and automatic track.
Some radars combine the previously described
manual operations and lock on mode into one mode
called acquisition. The term acquisition, as used in
operation of a radar set, refers to a momentary mode
of operation. The time period for acquisition begins
at the moment the operator depresses a control switch
transferring antenna control from automatic search to
manual search. During this period, the operator has
complete control of antenna position, both in azimuth
and elevation, and may also control a symbol on the
indicator called an acquisition symbol. If the
operator places the acquisition symbol over the
selected target, it causes coincidence between the
tracking gate and the target in the range and tracking
circuits of the radar. Acquisition is complete when
lock on occurs, and the system switches to automatic
track. Lock on is accomplished by a change in the
B-scope presentation and the blanking of the PPI
scope. However, in the trainer, manual track may be
continued after leek on, if desired.
On the B-scope, the acquisition symbol is
removed and replaced with a range strobe or notch
superimposed on the target, as shown in figure 3-13.
The artificial horizon remains as before. Note there
are two symbols present now that were not previously
present. One of these is a small dot, called a steering
dot. The purpose of the steering dot is to indicate
antenna position, which also presents target position
with respect to the attacking aircraft. For a pure
pursuit course, the pilot need only maneuver the
aircraft to cause the steering dot to remain in the
center of the scope. When the steering dot is in the
center of the scope on a pure pursuit course, the target
is dead ahead of the attacking aircraft.
The second symbol, which was not present in the
previous modes, is a circle. This circle is called a
range circle, and its diameter is proportional to
range. Normally, lock on occurs at near maximum
range, which produces a range circle of maximum
size. As the range between the attacking aircraft and
the target decreases, the diameter of the circle also
decreases, keeping the operator informed of the range
to the target. In addition to these symbols, two other
indications of range are presented at the time the radar
locks on. A light, known as the lock on or acquisition
light, is illuminated when the target has been acquired
and lock on has been accomplished. Range is also
presented in digital form in a small window similar to
the mileage counter of an automobile.
Fire Control (Automatic Track)
The automatic track submode of fire control
results from the manual track mode upon release of
the manual controls (range and azimuth). Remember,
prior to automatic tracking, the antenna had been
manually controlled in both elevation and azimuth,
and the range strobe (notch) had been controlled by
the range control. To initiate automatic tracking, the
operator releases the manual controls, and the radar
switches to automatic track. At this time, the antenna
is caused to track the target by the antenna servo
system error circuits.
Range tracking is accomplished in the range
tracking circuits. Automatic tracking continues until
one of three things occurs. First, lock on will be lost
if the attacking aircraft is closing on the target at a rate
greater than 700 knots, or if an opening rate greater
than 200 knots should occur. Second, the target will
be lost, and the radar will unlock if the target does not
remain within the tracking window (antenna limits in
azimuth and elevation). Finally, the target will be lost
if the range exceeds maximum tracking range.
Figure 3-13.-B-scan presentation after lock on.