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6-4
False Echo by Sidelobe
An ultrasonic wave is emitted only in the direction set by the
TILT lever, however there are some emissions outside the main
beam. These are called sidelobes. The ennergy of the sidelobe is
fairly weak but when the water is comparatively shallow and the
bottom is rocky and hard, strong signals are detected by the
sidelobe. These are represented on the display as a false echo as
shown below.
Sidelobe
Sidelobe
Mainlobe
echo
Sidelobe
echo
The seabed echo
detected by sidelobe
appears at a certain
tilt angle when the
sidelobe points
vertically.
Figure 6-5 Sidelobe echoes
Noise and Interference
Interference from a sonar on board another ship appears on the
screen as shown in (A) below. This interference can be suppressed
by changing the TX CYCLE setting in the Scan menu. Interfer-
ence from electrical equipment on board own ship appears as
shown in (B) below. Noise from marine life appears on the dis-
play as shown in (C). Electrical interference and marine life noise
can be suppressed with IR on the Scan menu.
(A) Interference from
other sonar
(B) Electrical
interference
(C) Marine life noise
Figure 6-6 Noise and interference