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1-2
1.5 Radar Wave Speed and
Antenna Rotation Speed
The speed of the radar waves out to the
target and back again as echoes is
extremely fast compared to the speed of
rotation of the antenna. By the time radar
echoes have returned to the antenna, the
amount of antenna rotation after initial
transmission of the radar pulse is
extremely small.
1.6 The Radar Display
Targets are displayed on what is called a
Plan Position Indicator (PPI). This display
is essentially a polar diagram, with the
transmitting ship’s position at the center.
Images of target echoes are received and
displayed at their relative bearings, and at
their distance from the PPI center.
With a continuous display of the images of
targets, the motion of the transmitting ship
is also displayed.
A
B
C
D
Own ship
(radar)
D
A
B
C
Heading marker
Targets
Own ship
in center
Range and bearing
of a target, relative
to own ship, are
readable on the PPI.
(A) Bird's eye view of situation
(B) Radar picture of (A)
Figure 1-1 How radar works