Eagle Electronics UltraNavGPS a

Weak bottom

echo, digital readings erratic, or no fish signals (cont.):

2. Electrical noisefromthe

boat's motorcan interfere with the sonar. This causes

the sonar to automatically increase its Discrimination or noise

rejection feature.

This can cause the unit to eliminate weakersignals

such as fish oreven structure

from the display.

3. Thewatermay bedeeperthanthe

sonar's abilitytofind

the bottom. If the sonar

can't find the bottom

signal

while ft's in the automatic

mode, the digital

will flash

continuously. It

may change

the

range

to

limits

fargreaterthan

the

wateryou

are

in. If this happens, place

the unit in the manual mode, then

change

the

range

a

realisticone,

(forexample, 0-1 OOfeet) and increasethe

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

waterdisruptthe sonarsignals, interfering

with its

abilityto

findthe

bottom orother

targets. The technical term for this Is 'Cavitation'.

2. Electrical noise fromthe boat's motorcan interfere with the sonar. This causes

the sonarto automatically

increase its Discrimination or noise rejection feature.

This can cause the unit to eliminate

weakersignals

such as fish oreven structure

from

the

display.

Try using resistorspark 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. See the Fish Arch section in your

owners

manual for more information.

2. The sensitivity may

not be high

enough. in orderforthe 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

displays

the fish only

when it is in the center of the cone.

3. Use the Zoom feature. It is much easierto

display

fish arches when zoomed

in on a small

range of waterthan a

large

one. For

example, you

will

have much

better luck

seeing

fish arches with a 30 to 60 foot range

than a

0

toGa

foot

range.

This

enlarges

the

targets, allowing the display to show much more detail.

4. The boat must be

moving

at a

siowtroUing

speed

to see fish arches. If the boat

motionless, fish stay

the

cone,

showing on the

display

as

straight

horizontal

lines.

ELECTRICAL NOISE

A

majorcause

of sonar

problems

is electrical noise. This

usually appears

on the

sonar's

display

as random patterns

of dots or lines. in severe

cases, it can

completely

cover the

screen with black

dots, or cause the unit

operate

erraticly.

or not at all.

To eliminate or minimize the effects of electrical noise, first

try

to determine the

cause. With the boat at rest in

the

water,

the first

thing you

should do is turn all

electrical equipment

on the boat off. Make certain the

engine

is

off, also. Turn

onyoursonarunit,thentumASP(AdvancedSignaiProcessing)off.

Thereshould

be a

steady

bottom

signal on the

display. Now

turn on each piece

of electrical

equipment

on the boat and view the effect on the sonar's

display. For

example,

turn on the

bilge pump

and viewthe

sonardisplayfor

noise. If no noise is

present,

turn the

pump

off, then turn on the

VHF

radio

and transmit. Keep doing

this until

all electrical equipment

has been turned

on, their effect on the sonar

display

noted, then turned

off.

if

you

find noise interference from

an electrical instrument, trolling

motor, pump,

radio, tryto isolatethe

problem.

You can usuallyre-routethe

sonarunit's

power

cable and transducercabie

away

from the

wiring that Is

causing

the interference.

VHF radio antenna cables radiate noise when

transmitting, so be certain to

keep

the sonar's wires

awayfrom

it. You

mayneedto

route the

sonarunit's

powercabie

directly

to the

battery

to isolate it from other

wiring

on the boat.

If no noise displays

on the sonar

unitfromelectricalequipment,

then rnakecertain

everything except

the sonar unit is

turned

off, then start the

engine. Increase the

RPM with the

gearshift

in neutral. If noise appears

on the

display,

the

problem

could be one of three things; spark plugs, alternator, or tachometer

wiring. Try

using resistorspark plugs, aiternatorfiiters, orrouting the sonarunit's

powercable

away

from engine wiring. Again, routing

the

power

cable

directly

to the

battery

helps

eliminate noise problems. Make certain to usethe in-line fuse

suphed

with

the unit

when

wiring

the

power

cable to the battery.

When no noise appears

on thesonarunit afterail of the abovetests,

thenthe noise

source is probably cavitation. Many

novices or

persons with limited

experience

make

hasty

sonar installations which function

perfectly in shallow

water,

orwhen

the boat is at rest. In

nearly

all

cases, the cause of the malfunction will be the

location and/or angle

of the

transducer. The face of the transducer

must be

placed

in a location that has a smooth flow of water at all boat

speeds.

Read your

transducer owners manual for the best

mounting position.

36 37

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