Furuno MODEL CSH-73 Rejecting Sonar Interference and Noise, Data setting window TVGTX, Output

Suppressing Seabed and Sea Surface Reflections in Shallow Waters

Data setting window: TVG•TX, OUTPUT

In shallow fishing grounds with hard or rocky bottom, seabed reflections often interfere with wanted fish echoes and they can not be eliminated sufficiently with the aforementioned TVG and AGC controls, especially when the TILT is set to a larger angle in order to track fish schools approaching within 400 m. In such cases try to reduce the output power by adjusting the OUTPUT control instead of turning down the gain. The picture becomes clearer when output power is reduced rather than when the GAIN is decreased as illustrated below.

WRONG

METHOD	Fish echo	Seabed echo
	TVG and AGC	False seabed echo
		Surface echo
	adjusted with
	OUTPUT kept high

CORRECT
METHOD	Fish echo
	OUTPUT decreased
	with GAIN kept
	constant

Figure 3-3 How to suppress seabed and sea surface reflections in shallow waters

Rejecting Sonar Interference and Noise

While observing the sonar picture, you may encounter occasional or intermittent noise and interference. These are mostly caused by on-board electronic equipment, engine or propeller noise, or electrical noise from other sonars being operated nearby.

3-4