Humminbird 161 - Manual (Page 93)

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Finding the Cause of Noise
Electrical noise usually affects the display with many black dots at high speeds, and high
sensitivity readings. One or more of the following sources can cause noise or
interference:
Possible Source of Noise Isolation
Other electronic devices
The boat’s engine
Cavitation from the
boat’s propeller
Turn off any nearby electronic devices to see if the
problem goes away, then turn them on one at a
time to see if the noise re-appears.
To determine whether the boat’s engine is the
source of the noise, increase the RPMs while the
boat is in neutral and stationary to see if the noise
increases proportionately; if noise appears when
you rev the engine, the problem could be the
spark plugs, alternator, or tachometer wiring.
Replace the spark plugs with resistor plugs, install
an alternator filter, or route the control head
power and transducer cables away from the
engine wiring.
Turbulence created by the propeller can cause
noise; make sure the transducer is mounted at
least 15” (38 cm) from the propeller, and that the
water flows smoothly over the face of the
transducer at all times.