Onwa KF-667 manual Surface Noise/Aeration

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3.4 Surface Noise/Aeration

When the waters are rough or the boat passes over a wake, surface noise may appear near the zero line. As surface turbulence is acoustically equivalent to running into a brick wall, the bottom echo will be displayed intermittently. Similar noise sometimes appears when a water temperature difference (thermocline) exists. Different species of fish tend to prefer different temperature zones, so the thermocline may be useful to help identify target fish. 200KHz tends to show shallow thermoclines better than 50KHz.

In rough waters the display is occasionally interrupted due to below-the-ship air bubbles obstructing the sound path. This also occurs when the boat makes a quick turn or reverses movement. Lowering the picture advance speed may reduce the interruption. However, reconsideration of the transducer installation may be necessary if the interruption occurs frequently.

Surface noise

Caused by aerated water

Thermocline

3-2

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Contents Model KF-667 Safety Instructions Table of Contents Introduction FeaturesPage Principle of Operation Display Unit System ConfigurationPower TransducerTD/Temp Control Function CONTROLS, IndicationsBrill Voltage IndicationsDisplay mode selection Turning the Power On/OffAdjusting Brilliance Display Mode Selection, DescriptionDisplay mode description 200K, 50K high frequency, low frequency modeDual frequency mode Marker Zoom Zoom mode high or low frequencyEnabling automatic operation Adjusting GainAutomatic Operation How it worksSelecting Picture Advance Speed Display Range SelectionBasic range selection Range shifting Erasing Weak EchoesScope Display Measuring Depth to a Fish SchoolMenu selection Menu OperationSystem Menu Main menu descriptionMenu item Description System Menu System menu descriptionSuppressing Low Level Noise Suppressing InterferenceAlarms Alarm descriptionSelecting Background and Echo Colors Silencing the buzzer Activating/deactivating an alarmWhite Marker Bottom Echo Interpreting the DisplayZero Line Fish School EchoesSurface Noise/Aeration General checking MAINTENANCE,TROUBLESHOOTINGMaintenance Replacement of fuseMaintenance of the transducer CleaningBasic troubleshooting Basic TroubleshootingTransducer Check Water Temperature Sensor option CheckMENU1 Menu TreeKF-667 Specifications on Color Video SounderPower Supply Index