Furuno 821, 841 manual Nautical Chart and Radar Picture, Blind and shadow sectors

Page 35

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 scanner 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 3-7.

3.6Nautical Chart and Radar Picture

Under normal conditions, a picture which is similar to a nautical chart can be obtained on the radar display. However, a radar can- not:

show targets which are below the hori-

 

zon.

show a target which is hidden by a larger

 

one.

Vessel taller than wharf

Wharf

Wharf

Blind sector (no echo)

Mast, etc. in path of radar beam

Size of blind sector depends on target size and range.

• see around corners (for example, sea-

wall).

• distinguish between two targets which are

very close together, either in range or

bearing. For example, a vessel towing

another will probably appear as one ves-

sel, as both will be covered by the beam

at the same time.

The nautical chart and radar picture shown in Figure 3-8 are from the Kada Inland Sea in southwestern Japan.

Figure 3-7 Blind and shadow sectors

Black areas are strong reflection targets.

Coastline difficult to display.

Actual topography

Radar display

Figure 3-8 Nautical chart and associated

radar picture

24

Image 35
Contents Marine Radar First Edition AUG Useable Environment Safety ArrangementsElectrical Shock Hazard Ground both the Display Unit and the Antenna UnitTable of Contents Foreword FeaturesDisplay Unit SPECIFICATIONS- ModelAntenna Unit Transceiver Module contained in radomeVibration Power supply & power consumptionProtection features Warm-up time Modulator switching methodReceiver front end MIC Michoeave IC Bandwidth 7 MHz Duplexer Ambiont temperatureInterface Nmea Model 821/841 Page Model 821/841 ConfigurationPrinciple of Operation How radar works Control Description OperationTurning the Radar On Off Display Indications and MarkersSelecting the Range Adjusting LCD Backlighting and Display ToneAdjusting Control Panel Brilliance TransmittingSTC MAN Auto Adjusting GAIN, STC, A/C Rain and FTCHow to tune manually Tuning the ReceiverAdjusting A/C Rain Adjusting FTCMeasuring the Bearing Measuring the RangeTarget on collision course with your vessel? Menu OperationMenu description 11 Display modes Selecting the Display ModeCU course-up Selecting the Presentation ModeWindow Display WPT-UP waypoint-up Guard AlarmGuard Suppressing Radar InterferenceSelecting Pulselength Suppressing Noise InterferenceOff Centering the Display Navigation Data Display Echo TrailsPress the Menu key Select Nav Data and press the ENT key Echo Stretch magnifying long range echoesWatchman Selecting Unit of Measurement for RangeSelecting Bearing Reference Displaying Navigation Data During Stand-by Erasing the Heading MarkerDeselecting Ranges Displaying Cursor Position, Range and Bearing to Cursor Visual Alarm IndicationsOutputting Cursor Position to Navigator Super-refraction Interpreting the DisplayRadar Wave and Radar Horizon Target Properties and Radar Wave ReflectionFalse Echoes Bearing ResolutionRange Resolution Multiple echoes Blind and shadow sectors Nautical Chart and Radar PictureTroubleshooting procedure Maintenance & TroubleshootingSafety Information Forming any maintenance orReplacing the Fuse Preventative MaintenanceTroubleshooting table TroubleshootingSelf Test Self TestAntenna Unit Installation InstallationVent tube Removing packing materialsMounting platform How to fasten the radome base To the mounting platform Ships bow Removing packing materials 10 Antenna unit Model 841, inside view, shield cover removed 12 Optional mounting bracket installation for sailboat Display Unit Installation 13 How to mount the display unit 14 Display unit, rear view Procedure Option connectorInstallation Check List Displaying the Installation Menus Initial Adjustment of PictureRelative Bearing Alignment Entering Initial SettingsSweep Timing Closing the Installation MenusSignal cable connection Page Page Page Page Page Page Page