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2. RADAR, CHART RADAR OPERATION
2-60
2.38.2 False echoes
Occasionally echo signals appear on the screen at positions where there is no target
or disappear even if there are targets. They are, however, recognized if you under-
stand the reason why they are displayed. Typical false echoes are shown below.
Multiple echoes
Multiple echoes occur when a transmitted pulse returns from a solid object like a large
ship, bridge, or breakwater. A second, a third or more echoes may be observed on the
display at double, triple or other multiples of the actual range of the target as shown
below. Multiple reflection echoes can be reduced and often removed by decreasing
the gain (sensitivity) or properly adjusting the sea clutter.
Sidelobe echoes
Every time the radar pulse is transmitted, some radiation escapes on each side of the
beam, called "sidelobes." If a target exists where it can be detected by the side lobes
as well as the main lobe, the side echoes may be represented on both sides of the true
echo at the same range. Side lobes show usually only on short ranges and from strong
targets. They can be reduced through careful reduction of the gain or sea clutter.
Own ship
Target
True
echo
Multiple
echo
Target B
(True)
Target B
(Spurious)
Target A