15
2
BASIC OPERATION
Basic radar theory
Radar finds targets by receiving electromagnetic radiation reflected from large vessels, bridges, or other nearby
metal objects. Receiving unwanted reflections from some objects may cause false echoes on screens where the
target does not exist.
By understanding these phenomena logically and adjusting the radar function appropriately, some of these false
echoes can be reduced.
D
Multiple echoes
Multiple echoes may be displayed when a short-range
and strong echo is received from a vessel, a bridge, or
a breakwater.
Multiple echoes will be displayed beyond the target’s
true echo point on the same bearing of a large target.
You can reduce them by properly adjusting
SEA
/
control.
See page 8 for more information on
SEA
/
control.
D
Sidelobe echoes
Radiation escapes on both sides of the beam in the
sidelobe. If a target reflects this radiation, it will be
displayed on the screen as an echo.
Sidelobe echoes usually occur as a result of large
(strongly reflecting) targets at a short distance. You
can reduce them by properly adjusting
SEA
/
control.
See page 8 for more information on
SEA
/
control.
D
Indirect echoes
Indirect echoes may be returned from a passing
vessel or from a reflective surface such as the mast of
your vessel.
Indirect echoes from the reflective surface appear in
different orientations than direct (true) echoes, but the
distance is approximately the same for both.
Your vessel
A target
True
echo
Multiple
echoes
Sidelobes Main
beam
True echo
Sidelobe
echoes
Mast or similar
obstruction
Scanner
A target
True
echo
False
echo
A target
Bridge
Your
vessel
Indirect
reflection
Mirrored image
of the target
Indirect echo
True echo
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