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The picture menu
Adjusting the gain (strong echoes)
Page 28
You can adjust the appearance of echoes in five different ways:
•
gain (for high intensity echoes)
•
clutter (for low intensity echoes)
•
noise limiter (for interference)
•
hue (to choose colors and white level)
•
signal level (to remove weak echoes)
Gain and clutter changes are applied only to new echoes as
they appear on the right side of the screen—earlier echoes are
not affected.
When you override the gain's automatic settings, the tabs on the
PICTURE
key and
cating the system is no longer in automatic mode. When you turn
the noise limiter on, only the
to yellow. Changing the hue or adjusting the signal level has no
effect on the operating mode (the tabs stay green).
The gain setting selects the echo strengths that will be
displayed using the top color in the color bar (the strongest
echoes). Any echoes stronger than this selection will use the
same color and no detail can be distinguished. The gain is
usually set so that seabed echoes are displayed in brown, the
strongest level.
The gain can be also be set automatically by pressing the
AUTO key. This will provide an excellent picture under most
conditions, and will allow the 491 to reliably detect the seabed
depth.
Gain is normally adjusted in conjunction with clutter, as
described on the next page, to maximize its effectiveness.
To adjust the gain:
1. On the ECHO screen, press PICTURE.
2. On the PICTURE screen, press GAIN.
NOTE:
AUTO
key change from green to yellow, indi-
PICTURE
key tab changes from green
491 Echo Sounder Operations Manual
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Troubleshooting
