Lowrance electronic LCX-15MT - Manual (Page 64)

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3. The water may be deeper than the sonar’s ability to find the bottom. If
the sonar can’t find the bottom signal while it’s in the automatic mode,
the digital will flash continuously. It may change the range to limits far
greater than the water you are in. If this happens, place the unit in the
manual mode, then change the range to a realistic one, (for example,
0-100 feet) and increase the sensitivity. As you move into shallower
water, a bottom signal should appear.
4. Check the battery voltage. If the voltage drops, the unit’s transmitter
power also drops, reducing its ability to find the bottom or targets.
Bottom echo disappears at high speeds or erratic digital reading or
weak bottom echo while boat is moving
1. The transducer may be in turbulent water. It must be mounted in a
smooth flow of water in order for the sonar to work at all boat speeds.
Air bubbles in the water disrupt the sonar signals, interfering with its
ability to find the bottom or other targets. The technical term for this is
Cavitation.
2. Electrical noise from the boat’s motor can interfere with the sonar. This
causes the sonar to automatically increase its Discrimination or noise
rejection feature. This can cause the unit to eliminate weaker signals
such as fish or even structure from the display. Try using resistor spark
plugs or routing the sonar unit’s power and transducer cables away
from other electrical wiring on the boat.
No fish arches when the Fish ID feature is off:
1. Make certain transducer is pointing straight down. This is the most
common problem if a partial arch is displayed.
2. The sensitivity may not be high enough. In order for the unit to display a
fish arch, it has to be able to receive the fish’s echo from the time it
enters the cone until it leaves. If the sensitivity is not high enough, the
unit shows the fish only when it is in the center of the cone.
3. Use the Zoom feature. It is much easier to display fish arches when
zoomed in on a small range of water than a large one. For example,
you will have much better luck seeing fish arches with a 30 to 60 foot
range than a 0 to 60 foot range. This enlarges the targets, allowing the
display to show much more detail.
4. The boat must be moving at a slow trolling speed to see fish arches. If
the boat is motionless, fish stay in the cone, showing on the screen as
straight horizontal lines.