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THE A SCOPE | Up
Neets Module 18-Radar Principles | Next
PLAN POSITION INDICATOR (PPI) |
3-3
Figure 3-1.—A scope.
The A-scope normally uses an electrostatic-deflection crt. The sweep is produced by applying a
sawtooth voltage to the horizontal deflection plates. The electrical length (time duration) of the sawtooth
voltage determines the total amount of range displayed on the crt face.
The ranges of individual targets on an A-scope are usually determined by using a movable range gate
or step that is superimposed on the sweep. Ranging circuits will be discussed in more detail later in this
section.
RANGE-HEIGHT INDICATOR (RHI)
The range-height indicator (rhi) scope, shown in figure 3-2, is used with height-finding search radars
to obtain altitude information. The rhi is a two-dimensional presentation indicating target range and
altitude. The sweep originates in the lower left side of the scope. It moves across the scope, to the right, at
an angle that is the same as the angle of transmission of the height-finding radar. The line of sight to the
horizon is indicated by the bottom horizontal line. The area directly overhead is straight up the left side of
the scope. Target echoes are displayed on the scope as vertical PIPS or BLIPS (spots of increased
intensity that indicate a target location). The operator determines altitude by adjusting a movable height
line to the point where it bisects the center of the blip. Target height is then read directly from an altitude
dial or digital readout. Vertical range markers are also provided to estimate target range.
Figure 3-2.—RHI scope.
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