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2.2 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 understand the
reason why they are displayed. Typical false echoes are shown below.
2.2.1 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 (sen-
sitivity) or properly adjusting the [A/C SEA] control.
Own ship
Target
True
echo
Multiple
echo
Figure 2-2 Multiple echoes
2.2.2 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. Sidelobes show usually only on short ranges and from strong targets.
They can be reduced through careful reduction of the gain or proper adjustment of the A/
C SEA control.
Target B
(True)
Target B
(Spurious)
Target A
Figure 2-3 Sidelobe echoes