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2. FINE TUNING THE SONAR PICTURE
2-5
2.5 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.
2.5.1 Identifying noise source
To eliminate noise effectively, you should first identify the noise source.
• Turn off [TRANSMISSION] in the [SONAR] menu to stop transmission and operate
all on board equipment one by one while observing the picture.
• Run the boat at various speeds to check if the noise is speed dependent.
If neither of the above two steps affects on the picture, adjust the [INT REJECT] (In-
terference Rejector), [NOISE LIMITER] or [TX CYCLE] on the [SONAR] menu as ap-
propriate.
2.5.2 Rejecting noise with the interference rejector
This control is similar to the interference rejector on echo sounders and radars. It is
effective for rejecting random noise and sea surface reflections in rough sea condi-
tions. Set the interference rejector so that noise is just eliminated. Do not use an un-
necessarily high setting since small wanted echoes may also be rejected.
1. Press the MENU key.
2. Use the RANGE control to choose [MENU MODE] at the top of the screen.
3. Use the GAIN control to choose [SONAR] to display the [SONAR] menu.
4. Use the RANGE control to choose [INT REJECT].
5. Use the GAIN control to set interference rejection level, from 0 (OFF) to 3 (highest
degree of suppression).
6. Press the MENU key to close the menu.
2.5.3 Rejecting noise with the noise limiter
Weak, unwanted reflections, colored light blue or green, are displayed when water is
contaminated or plankton layers exist or due to ship's noise.
1. Press the MENU key. The last-used menu appears.
2. Use the RANGE control to choose [MENU MODE] at the top of the screen.
3. Use the GAIN control to choose [SONAR] to display the [SONAR] menu.
4. Use the RANGE control to choose [NOISE LIMITER].
5. Use the GAIN control to set noise limiter level. The setting range is 0-10 and the
higher the figure the greater the degree of suppression.
6. Press the MENU key to close the menu.