Furuno CSH-53 manual False Echo by Sidelobe, Noise and Interference

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False Echo by Sidelobe

An ultrasonic wave is emitted only in the direction set by the TILT lever, however there are some emissions outside the main beam. These are called sidelobes. The energy of the sidelobe is fairly weak but when the water is comparatively shallow and the bottom is rocky and hard, strong signals are detected by the sidelobe. These are represented on the display as a false echo as shown below.

		Mainlobe
Sidelobe	Sidelobe	echo
	Sidelobe
		Sidelobe
		echo

The seabed echo detected by sidelobe appears at a certain tilt angle when the sidelobe points vertically.

Figure 11-5 Sidelobe echoes

Noise and Interference

Interference from a sonar on board another ship appears on the screen as shown in (A) below. This interference can be suppressed by changing the CYCLE setting in TVG•TX on the data setting window. Interference from electrical equipment on board own ship appears as shown in (B) below. Noise from marine life ap- pears on the display as shown in (C). Electrical interference and marine life noise can be suppressed with IR on the SIGNAL menu in the data setting window.

(A) Interference from	(B) Electrical	(C) Marine life noise
other sonar	interference

Figure 11-6 Noise and interference

11-4

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Contents Color Scanning Sonar 00080807301 Safety Instructions Table of Contents Iii Self Tests Foreword System Configuration Control Description Main Panel Main panel control descriptionControl Function Sub Panel ENDSub Panel 2 data setting window Main Setting Description Normal Main Setting Description Normal Sub Range Remote Control Box + +Turning the Power On/Off Adjusting Screen Brilliance, Control Panel BacklightingOperational Overview Lowering the TransducerSelecting a Display Mode Display mode descriptionSetting the Tilt Angle Selecting a Display RangeSeabed echo and tilt angle How to discriminate fish echoes from the seabed Points to considerTilt angle for surface fish Tilt angle and sea surface reflectionsSuitable tilt angle Tilt angle and beam coverageAdjusting the Gain Measuring Range and Bearing to a TargetThis page is intentionally left blank Fine Tuning the Picture How to adjust TVGEliminating Unwanted Feeble Echoes Page AGC data setting window SIGNAL, Signal Pulselength data setting window TVG TX, PL2AGC data setting window SIGNAL, Signal Process Suppressing Seabed TailData setting window TVGTX, Output Rejecting Sonar Interference and NoiseIdentifying noise source Changing Tx cycle data setting window Tvgtx CycleSetting F-shift data setting window Sonrbeam Noise limiter data setting window SIGNAL, Signal ProcessMarks, Data and Display Mode Normal display modeMarks and Data Normal display mode w/text Echo sounder combination displayPermanently Displayed Marks and Data History displayErasable Marks and Data Bearing marker Range marker Mark Description Range R Auto Tilt ± Auto Scan ± Gain Brill TVG TVG DIM This page is intentionally left blank Menu Overview User Menu OperationMenu screen location and display mode User Menu Hist DSP/GRPHUser Menu Description User menu descriptionCurrent VEC System Menu Description System menu can be displayed by pressing Menu + cMenu Description ES/NET REC Data SET Menu Description Data SET menu can be display by pressing Menu + dMenu NET Shoot Init SET/TEST Menu Description Init SET/TEST menu can be displayed by pressing Menu + onDefaults Function Keys Programming the Function KeysFunction Key Fine Tuning Replaying a Function KeySaving Function Key Settings to a Memory Card Replaying Function Key Settings from a Memory CardThis page is intentionally left blank How to find fish school center Advanced Level OperationFinding Fish School Center Tracking a Fish School target lock Tracking a fish schoolChoosing target lock mode Target lock mark appearanceErasing target lock mark Tracking target lock mark Target lock and tilt angleSetting target lock conditions System Menu Target LockDescription of target lock items Detecting Fish Schools Aurally Fish Alarm How to set the fish alarm zoneHow to relocate fish schools Relocating Fish School for Easy ObservationComparing of Fish School Concentration Estimate marks and their dataHow to measure fish speed Measuring Fish School SpeedEvent Mark 10 Event marksEntering an event mark Erasing an event markTrue Motion Display 12 True motion displayPlotting Net Location Mark 13 Net location markObserving Net Behavior 14 Net behaviorBoosting Tx Power Reducing Sea Surface ReflectionsThis page is intentionally left blank PORT/STARBOARD, Horizontal Slice Displays Port/Starboard displayHorizontal slice display Horizontal slice displaySAVING, Replaying Picture Initializing Memory CardsSaving the Picture Transferring Echo Data from Internal Memory to Memory CardNet shooting data contents Saving Net Shooting DataHow net shooting data is saved Transferring net shooting data to memory cardDeleting Memory Card Contents Replaying Saved DataTurning marks on/off through the data setting window Turning MARKS, Data ON/OFFTurning marks on/off through the user menu This page is intentionally left blank Interpreting the Display Seabed EchoesFish Schools Midwater, bottom fish Tilt angle 30 or moreSea Surface Reflections WakeFalse Echo by Sidelobe Noise and InterferenceOvervoltage Warning Unretracted Transducer WarningRaise/Lower Control Box of the Hull Unit Self Tests Self Test Description Single testContinuous test Panel test Color testGray test SIO testInterface Unit CS-120A Self Test Interface unit CS-120A, cover openedThis page is intentionally left blank Input Data Selection Selection of Data on Interface Unit CS-120ASetting Distances Between Net Sonde Transmitters How to set net sonde transmitter distancesMaintenance Hull Unit Maintenance Zinc block near the transducer must be replaced yearlyReplacement of Fuse, Memory Card Battery 15-4 Menu Tree User MenuData SET Menu Init SET/TEST Menu System Menu Previous This page is intentionally left blank Specifications GeneralDisplay Environmental Condition Index 12-7