NorthStar Navigation Echo Sounder NorthStar 491 - Manual (Page 61)

491 Echo Sounder Operations Manual Page 57
4. Follow the instructions below for each of these five
settings.
Fish alarm window
Setting the alarm’s
echo strength level
To set the fish alarm’s minimum echo-strength level:
1. At the FISH ALARM window, press SET ALARM LEVEL.
2. Press the CURSOR PAD up and down to set the echo
strength level from 1 to 15, as represented on the vertical
color bar.
Echoes received that are strong enough to be within the
crosshatched area on the vertical bar will cause an alarm
(weaker echoes will be ignored).
Setting the upper
and lower marker
depths
The fish alarm will sound only when there are echoes inside
(or optionally, outside) the upper and lower markers. These
markers are displayed on the ECHO screens.
To set the depth of the upper marker:
1. At the FISH ALARM window, press SET UPPER MKR.
The upper marker window is highlighted in black.