Furuno CSH-83, CSH-84 manual False Echo by Sidelobe, Noise and Interference

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 energy 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.

		Mainlobe
Mainlobe	Sidelobe	echo
		Sidelobe
		echo

The seabed echo detected by sidelobe appears at a certain tilt angle when the sidelobe points vertically.

Figure 11-5 Sidelobe echoes

Noise and Interference

Interference from a sonar on another ship appears on the screen as shown in (A) below. This interference can be suppressed by changing the CYCLE setting in TVG•TX on the data setting window. Interference from electrical equipment on board own ship appears as shown in (B) below. Noise from marine life ap- pears on the display as shown in (C). Electrical interference and marine life noise can be suppressed with IR on the SIGNAL menu in the data setting window.

(A) Interference from	(B) Electrical	(C) Marine life noise
other sonar	interference

Figure 11-6 Noise and interference

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