Furuno GD-1700C - Manual (Page 157)

4. VIDEO SOUNDER OPERATION
4-13
4.7 Reducing Low Level Noise
Dots (light-blue on the color model) may appear over most of the screen. This is
mainly due to sediment in the water or noise. This noise can be suppressed by
adjusting CLUTTER on the SOUNDER menu.
Appearance of clutter
When the sounder mode is Auto, the clutter suppression setting is fixed at AUTO.
To reduce low level noise in manual sounder operation do the following:
1. Press the [MENU] key.
2. Press the SOUNDER MENU soft key.
3. Select CLUTTER and press the EDIT soft key to show the clutter window.
CLUTTER
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00
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Clutter window
4. Use the cursor pad to select clutter rejection level desired; 0 (OFF) through
16, default setting, 9. The higher the number the higher the degree of
suppression. Note that the clutter suppressor may erase weak echoes.
Therefore, turn off the clutter when its use is not required.
5. Press the RETURN soft key followed by the [MENU] key to close the menu.
Note:
Unlike the signal level feature, clutter does not reduce echo colors.
However, if you do not wish to change the relation between weak and
strong echoes, use signal level instead.