Furuno CSH-83, CSH-84 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
Mainlobe	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 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

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Contents Color Scanning Sonar 00080806600 Safety Instructions Do not use the equipment for other than its intended purpose Table of Contents PORT/STARBOARD, Horizontal Slice Displays Self Tests This page is intentionally left blank Word to CSH-83/84 Owners FeaturesForeword System Configuration Standard OptionControl Layout on Display Unit and Remote Control Box Control DescriptionMain Panel Main panel control descriptionControl Function Sub Panel ENDSub Panel 2 data setting window Process SignalAGC 2AGCUP/TM AlarmSonar SonrbeamRemote Control Box + +Operational Overview Turning the Power On/OffAdjusting Screen Brilliance, Control Panel Backlighting Lowering the TransducerSelecting a Display Mode Display mode descriptionSeabed echo and tilt angle Setting the Tilt AngleSelecting a Display Range 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 TargetPage Eliminating Unwanted Feeble Echoes Fine Tuning the PictureHow to adjust TVG Page 2AGC data setting window SIGNAL, Signal Process AGC data setting window SIGNAL, SignalPulselength data setting window TVGTX,PL Suppressing Seabed TailIdentifying noise source Data setting window TVGTX, OutputRejecting Sonar Interference and Noise Changing Tx cycle data setting window Tvgtx CycleAdjusting Beamwidth Setting Noise limiter data setting window SignalMarks and Data Marks, Data and Display ModeNormal display mode Normal display mode w/text Echo sounder combination displayPermanently Displayed Marks and Data History displayErasable Marks and Data Mark/Data DescriptionBearing marker Mark Description Range R Auto Tilt Auto Scan Gain Brill TVG TVG DIM Page Menu Overview User Menu OperationMenu screen location and display mode User Menu Hist DSP/GRPHUser Menu Description Current VEC Save PictureTM DSP System Menu DescriptionFAR TVG Target LockBRG Readout Mark SizeMenu Description Data SET Menu Description Color CurveChange Color NET Sonde NET ShootPlan NET Plot CorrInit SET/TEST Menu Description NET REC DefaultsEcho Test Others Event KEYFunction 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 Finding Fish School Center How to find fish school centerAdvanced Level Operation Tracking a Fish School target lock Tracking a fish schoolErasing target lock mark Choosing target lock modeTarget lock mark appearance 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 behaviorTarget Slice Display No. Display Information ApplicationsThis page is intentionally left blank PORT/STARBOARD, Horizontal Slice Displays Port/Starboard displayHorizontal slice display Horizontal slice displayMemory Card Operations Initializing Memory CardsSaving the Picture Transferring Echo Data from Internal Memory to Memory CardHow net shooting data is saved Net shooting data contentsSaving Net Shooting Data Transferring net shooting data to memory cardDeleting Memory Card Contents Replaying Saved DataTurning marks on/off through the user menu Turning marks on/off through the data setting windowTurning MARKS, Data ON/OFF 10-2 Interpreting the Display Seabed EchoesFish Schools Sea surface fishSea Surface Reflections WakeFalse Echo by Sidelobe Noise and InterferenceOvervoltage Warning Unretracted Transducer WarningHow to manually raise the transducer Self Tests Opening the Self Test MenuContinuous test Self Test DescriptionSingle test Panel test Color testGray test SIO testInterface Unit CS-120A Self Test Interface unit CS-120A, cover opened13-6 Input Data Selection Selection of Data at Interface Unit CS-120ASetting Distances Between Net Sonde Transmitters How to set net sonde transmitter distancesMaintenance Display Unit MaintenanceHull Unit Maintenance Zinc block near the transducer must be replaced yearlyMenu Tree User MenuData SET Menu Init SET/TEST Menu System Menu Previous Page Specifications SP-1Display SP-2Hull Unit SP-3SP-4 Index 11-2IN-2