Contents
1 Welcome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Welcome to the Northstar 491 . . . . . . . . . . . . 2 Using this manual . . . . . . . . . . . . . . . . . . . . . . 2 Technical support . . . . . . . . . . . . . . . . . . . . . . 4 How echo sounding works . . . . . . . . . . . . . . . 5 Powering the 491 on and off . . . . . . . . . . . . . 7 Setting up the 491 . . . . . . . . . . . . . . . . . . . . . 7
2 Quick Start: Using the Echo Sounder . . . . . . . . . 11
Displaying the echo sounder’s picture . . . . . 12 Using demo mode . . . . . . . . . . . . . . . . . . . . . 14 Introducing the displayed information . . . . 15 Using automatic mode . . . . . . . . . . . . . . . . . 16 Changing the frequency of echoes . . . . . . . 17 Zooming in and out . . . . . . . . . . . . . . . . . . . 19 Setup functions . . . . . . . . . . . . . . . . . . . . . . . 22
3 Adjusting the Echo Sounder Picture . . . . . . . . . 27
The picture menu . . . . . . . . . . . . . . . . . . . . . 28 Adjusting the gain (strong echoes) . . . . . . . . 28 Adjusting the clutter (weak echoes) . . . . . . . 29 Adjusting the signal level (weak echoes) . . . 30 Suppressing interference (the noise limiter) . 31 Selecting the color bar (hue) and white level 32
4 Understanding Depth Settings . . . . . . . . . . . . . . 35
Viewing the seabed depth . . . . . . . . . . . . . . 36 Viewing the depth marker . . . . . . . . . . . . . . 36 Changing the depth settings . . . . . . . . . . . . 36 Setting the picture’s shift (starting depth) . . 37 Setting the picture’s range . . . . . . . . . . . . . . 38
5 Other Functions: Using the MORE key . . . . . . . 41
Using the MORE key . . . . . . . . . . . . . . . . . . . 42 Changing the advance speed . . . . . . . . . . . . 42 Displaying the
