3.At the GAIN window, press the CURSOR PAD left or right to adjust the gain, or use the KEYPAD to manually enter the desired gain value. The available settings range from zero (minimum) to 75 (maximum).
Gain window
The window shows the effect of adjusting the gain. The fish symbols near the bottom of the window represent various echo strengths, and the expanding and contracting color bar above shows the colors that will be used to display these echoes. As you adjust the gain to obtain the best looking picture, also watch the real echoes on the right side of the screen .
4. Press RETURN to go back to the ECHO screen.
When you adjust the gain, the color of the AUTO and PICTURE key tabs changes from green to yellow, since the echo sounder is no longer in automatic mode. Also, a yellow tab appears under the DEPTH key, indicating that the range setting is no longer automatically controlled and that the 491 may not always identify the bottom reliably.
Adjusting the clutter (weak echoes)
The clutter setting selects the echo strength that will be displayed using the bottom colors of the color bar (the weaker echoes). Any echoes weaker than this selection will not be
491 Echo Sounder Operations Manual | Page 29 |