Lowrance electronic LCX-15MT - Manual (Page 21)

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Transducer Frequency
This unit operates from both 200 kHz and 50 kHz. The default frequency
is 200 kHz. It’s best for use in shallow water. The 50 kHz frequency is best
for deep water, especially saltwater. Use the arrow keys to highlight the
desired frequency, then press the ENT key to select it.
Surface Clarity
The markings extending downward from the zero line on the chart are
called “surface clutter”. These markings are caused by wave action, boat
wakes, temperature inversion, and more.
The surface clarity control reduces or eliminates surface clutter signals
from the display. It does this by changing the sensitivity of the receiver,
decreasing it near the surface and gradually increasing it as the depth
increases. The maximum depth that the surface clarity control can affect
is 75% of the selected depth range. For example, on a 0 - 60 foot range
with surface clarity control set to high, surface clutter will be reduced down
to 45 feet.
There are three levels of surface clarity available: low, medium, or high. It
can also be turned off. The default level is low. To change it, highlight
“Surface Clarity” on the “Sonar Features” menu, then press the ENT key
to select it. Use the cursor keys to highlight the desired level of surface
clarity, then press the ENT key.
Noise Rejection
The automatic noise rejection system built into this unit constantly evalu-
ates the effects of boat speed, water conditions, and interference from
electrical and mechanical sources such as bilge pumps, engine ignition
systems and wiring, even engine vibration. It then works to reduce or
eliminate the negative effects on the sonar screen. This gives the best
display possible under most conditions.
The Noise Rejection system is an effective tool in combating noise. In
sonar terms, noise is any undesired marks on the display.
This unit has two levels of noise rejection: normal and high. It can also be
turned off. The default is normal. To change it, highlight “Noise Rejection”
on the “Sonar Features” menu, then press the ENT key to select it. Use
the cursor keys to highlight the desired level of noise rejection, then press
the ENT key.