Furuno 1942 MARK-2 manual Indirect Echoes, Blind and Shadow Sectors

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4.3 Indirect Echoes

Indirect echoes may be returned from either a passing ship or returned from a reflecting surface on your own ship, for example, a stack. In both cases, the echo will return from a legitimate contact to the scanner by the same indirect path. The echo will appear on the same bearing of the reflected surface, but at the same range as the direct echo. Figure 4-3 illustrates the effect of an indirect echo. Indirect echoes may be recognized as fol- lows:

they usually occur in a shadow sector

they appear on the bearing of the obstruc- tion but at the range of the legitimate con- tact

when plotted, their movements are usu- ally abnormal, and

their shapes may indicate they are not di- rect echoes.

Direct

Heading

path

marker

 

Target

Indirect path

Obstruction

Scanner (mast, funnel. etc.)

Indirect

Target

 

True

 

Indirect

echo

path

Direct

echo

 

 

path

 

 

Heading

Ownmarker ship

True echo

Bridge

Indirect

Indirectecho echo

Figure 4-3 Indirect echoes

4.4 Blind and Shadow Sectors

Funnels, stacks, masts, or derricks in the path of antenna may reduce the intensity of the radar beam. If the angle subtended at the antenna is more than a few degrees a blind sector may be produced. Within the blind sector small targets at close range may not be detected while larger targets at much greater ranges may be detected. See Figure 4-4.

Figure 4-4 Blind and shadow sectors

4-2

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Contents Marine Radar Page Worst case 1.70 m Stay away from transmitting scannerRadiator Distance to Nil Worst case 1.20 mUse the proper fuse Do not open the equipmentDo not disassemble or modify the equipment Keep heater away from equipmentCompliance with R&TTE Directive 1999/5/EC Features ForewordTable of Contents Menu Tree Menu KEYTable of Contents by INDICATION, Marker System Configuration Scanner UnitDisplay Unit How Radar Determines Range What is Radar?Principle of Operation How Radar Determines BearingHow radar works Basic Operation Control DescriptionStand-by Economy modeTurning the Radar On/Off TransmittingAdjusting the A/C SEA Control Reducing sea clutter Adjusting Picture BrillianceAdjusting Receiver Sensitivity Selecting the RangeTip for adjusting the A/C SEA Adjusting the A/C Rain Control Reducing rain clutterAdjusting the A/C SEA control Adjusting A/C RainMeasuring range by range rings Measuring the RangeErasing the Heading Marker, North Marker Measuring range by cursorUsing the Offset EBL Measuring the BearingCancelling offcentered picture Offcentering the PictureMeasuring range and bearing between two targets Cancelling zoom ZoomBasic Menu Operation Selecting the Presentation ModeMenu Operation Head upEcho Trail Magnifying Long Range Echoes echo stretchFixed time trail Cancelling echo trailSuppressing Radar Interference Continuous trailSelecting Pulsewidth Guard AlarmSetting a guard zone Selection of guard zone typeWatchman Silencing the audible alarmCancelling the guard zone and guard alarm How watchman worksTurning on watchman Cancelling watchmanDisplaying Navigation Data To turn navigation data on or offOther Menu Description Other Menu DescriptionSuppressing Noise Adjusting Brilliance of MarkersFunction Controls Outputting Target PositionFalse Echoes Multiple EchoesSide-lobe Echoes Indirect Echoes Blind and Shadow SectorsSummary to detect Sart response Sart Search and Rescue TransponderShowing Sart marks on the radar display General remarks on receiving SartThis page is intentionally left blank Maintenance & Troubleshooting Preventive MaintenanceReplacing the Fuse Troubleshooting But ThenSelf Test This page is intentionally left blank Operation of ARP-10 Option Display accuracy is affected by the followingARP-10 Menu Operation Principal specificationsGeneral Keys used for auto plotterDeactivating the auto plotter ARP MenuManual acquisition Setting auto acquisition areaAcquiring Targets Automatic acquisitionIndividual targets Displaying Target DataTerminating Tracking of Targets All targetsCPA/TCPA alarm Mode and Length of VectorsTrue or relative vector vector mode Past Position DisplayLost target alarm This page is intentionally left blank Specifications of Marine Radar Display Unit Dimensions and Mass Index IN-1Page Page Page 00080835401