Eagle SUPRAPRO I.D. Installation And Operation Instructions Manual - page 24
24
ELECTRICAL NOISE
A major cause 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 your
SupraPro I.D. on, then turn off ASP (Advanced Signal Processing). There should
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 view the sonar display for 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,
or radio, try to isolate the problem. You can usually re-route the sonar unit’s power
cable and transducer cable 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 away from it. You may need to route the sonar unit’s power cable
directly to the battery to isolate it from other wiring on the boat.
If no noise displays on the sonar unit from electrical equipment, then make certain
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 resistor spark plugs, alternator filters, or routing the sonar unit’s power cable
away from engine wiring. Again, routing the power cable directly to the battery
helps eliminate noise problems. Make certain to use the in-line fuse supplied
with the unit when wiring the power cable to the battery!
When no noise appears on the sonar unit after all of the above tests, then the noise
source is probably cavitation. Many novices or persons with limited experience
make hasty sonar installations which function perfectly in shallow water, or when
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 owner’s manual for the best mounting position.