Furuno 1942 MARK-2 manual Principle of Operation, What is Radar?, How Radar Determines Range

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1. PRINCIPLE OF OPERATION

1.1 What is Radar?

The term “RADAR” is an acronym meaning Radio Detection And Ranging. Although the basic principles of radar were developed dur- ing World War II, echoes as an aid to naviga- tion is not a new development.

1.2How Ships Determined Position Before Radar

Before the invention of radar, when running in fog near a rugged shoreline, ships would sound a short blast on their whistles, fire a shot, or strike a bell. The time between the origination of the sound and the returning of the echo indicated how far the ship was from the cliffs or the shore. The direction from which the echo was heard indicated the rela- tive bearing of the shore.

1.3How Radar Determines Range

Radar determines the distance to the target by calculating the time difference between the transmission of a radar signal and the recep- tion of the reflected echo. It is a known fact that radar waves travel at a nearly constant speed of 162,000 nautical miles per second. Therefore the time required for a transmitted signal to travel to the target and return as an echo to the source is a measure of the dis- tance to the target. Note that the echo makes a complete round trip, but only half the time of travel is needed to determine the one-way distance to the target. This radar automati- cally takes this into account in making the range calculation.

1.4How Radar Determines Bearing

The bearing to a target found by the radar is determined by the direction in which the ra- dar scanner is pointing when it emits an elec- tronic pulse and then receives a returning echo. Each time the scanner rotates pulses are transmitted in the full 360 degree circle, each pulse at a slightly different bearing from the previous one. Therefore, if one knows the direction in which the signal is sent out, one knows the direction from which the echo must return.

1.5Radar Wave Speed and Scanner Rotation Speed

Note that the speed of the radar waves out to the target and back again as echoes is extremely fast compared to the speed of ro- tation of the scanner. By the time radar ech- oes have returned to the scanner, the amount of scanner rotation after initial transmission of the radar pulse is extremely small.

1.6 The Radar Display

The range and bearing of a target is displayed on what is called a Plan Position Indicator (PPI). This display is essentially a polar dia- gram, with the transmitting ship’s position at the center. Images of target echoes are re- ceived and displayed at their relative bear- ings, and at their distance from the PPI center.

With a continuous display of the images of targets, the motion of the transmitting ship is also displayed.

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Contents Marine Radar Page Nil Worst case 1.20 m Stay away from transmitting scannerRadiator Distance to Worst case 1.70 mKeep heater away from equipment Do not open the equipmentDo not disassemble or modify the equipment Use the proper fuseCompliance with R&TTE Directive 1999/5/EC Foreword FeaturesTable of Contents Menu KEY Menu TreeTable of Contents by INDICATION, Marker Display Unit System ConfigurationScanner Unit How Radar Determines Bearing What is Radar?Principle of Operation How Radar Determines RangeHow radar works Control Description Basic OperationTransmitting Economy modeTurning the Radar On/Off Stand-bySelecting the Range Adjusting Picture BrillianceAdjusting Receiver Sensitivity Adjusting the A/C SEA Control Reducing sea clutterAdjusting A/C Rain Adjusting the A/C Rain Control Reducing rain clutterAdjusting the A/C SEA control Tip for adjusting the A/C SEAMeasuring range by cursor Measuring the RangeErasing the Heading Marker, North Marker Measuring range by range ringsMeasuring the Bearing Using the Offset EBLMeasuring range and bearing between two targets Cancelling offcentered pictureOffcentering the Picture Zoom Cancelling zoomHead up Selecting the Presentation ModeMenu Operation Basic Menu OperationMagnifying Long Range Echoes echo stretch Echo TrailContinuous trail Cancelling echo trailSuppressing Radar Interference Fixed time trailSelection of guard zone type Guard AlarmSetting a guard zone Selecting PulsewidthHow watchman works Silencing the audible alarmCancelling the guard zone and guard alarm WatchmanTo turn navigation data on or off Cancelling watchmanDisplaying Navigation Data Turning on watchmanOther Menu Description Other Menu DescriptionOutputting Target Position Adjusting Brilliance of MarkersFunction Controls Suppressing NoiseSide-lobe Echoes False EchoesMultiple Echoes Blind and Shadow Sectors Indirect EchoesGeneral remarks on receiving Sart Sart Search and Rescue TransponderShowing Sart marks on the radar display Summary to detect Sart responseThis page is intentionally left blank Replacing the Fuse Maintenance & TroubleshootingPreventive Maintenance But Then TroubleshootingSelf Test This page is intentionally left blank Display accuracy is affected by the following Operation of ARP-10 OptionKeys used for auto plotter Principal specificationsGeneral ARP-10 Menu OperationARP Menu Deactivating the auto plotterAutomatic acquisition Setting auto acquisition areaAcquiring Targets Manual acquisitionAll targets Displaying Target DataTerminating Tracking of Targets Individual targetsPast Position Display Mode and Length of VectorsTrue or relative vector vector mode CPA/TCPA alarmLost target alarm This page is intentionally left blank Specifications of Marine Radar Display Unit Dimensions and Mass IN-1 IndexPage Page Page 00080835401