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Basic Radar Operation

By Terry Sparks Commander USN Retired. Basic Radar Operation. Terry Sparks & Radar. Navy trained to operate and maintain Radar Operated and maintained Radar on 2 US Navy Submarines Trained several groups on Radar Operation Supervised Maneuvering Watch Radar Tracking

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Basic Radar Operation

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  1. By Terry Sparks Commander USN Retired Basic Radar Operation

  2. Terry Sparks & Radar • Navy trained to operate and maintain Radar • Operated and maintained Radar on 2 US Navy Submarines • Trained several groups on Radar Operation • Supervised Maneuvering Watch Radar Tracking • BSEE from Washington State • Hold General Class FCC License with Radar Endorsement • Test and maintain all transmitting equipment in US

  3. Agenda • How does Radar work? • What Can I Expect? • Controls and Functions • Contact Avoidance with Radar • Using EBL and VRM • Navigation with Radar

  4. Rules of Engagement I assume there are a lot of different levels of skill here. • So: • I will be asking questions as we go through the lesson. • If you are sure you know the answer, hold back. • If you know the answer just raise your hand so I will know who not to call on.

  5. How does Radar work?

  6. Radar • GPS can pinpoint your location on earth • However it is utterly blind to your surroundings • It can not see: • Nearby boats • Squalls & Fog • Port Entry Hazards • When charts are not accurate

  7. Radar • AIS is becoming a poor substitute for Radar • Great information about ships that have AIS • Nothing on the rest • False sense of security • Tells you nothing about weather

  8. What is Radar • Acronym: RAdio Detection and Ranging (Radar) • In use since WWII • Similar to Sonar, but at a higher frequency • Radio waves travel at 162,000 nm/Second • 300,000,000 Meters/Second • Bounce Back from objects • Time for return is time for 2 times the distance of Object

  9. Radar works on time measurement Other vessel Radar Antenna Radar Transmits a pulses then listens for a defined period. t1 t2 Next Radar Pulse Output Reflected Pulse Arrives back to Radar Radar Pulse Output Listen period t1 t2 tMax For a 26 nm radar tMax is approximately equal to 0.000321 seconds. ~3KHz Distance to contact = ½ total time X 162,000 nm/Sec

  10. What Can I Expect?

  11. Radio Waves • HF • Marine SSB or Ham • Transmits along the surface of the earth • Bounces back to earth off the atmosphere • Could back and forth bounce all the way around the earth • VHF and UHF • Marine VHF radio and Ham radio • Line of site • Out to Horizon only, then into space • Radar • Also Line of site • Out to Horizon only, plus a small bit • Then into space

  12. Prospective of the Horizon • Horizon in NM= • Distance to the horizon in Nautical Miles • 1.17 X square root Sum of heights • Height of Self + Height of other • So if you are both at 8 feet • 1.17 X SQRT(8 + 8) • 1.17 X 4 • = 4.68 NM • 50 foot Antenna/Structure at both locations = 11.7 NM • My antenna at 25’ / 50’ vessel on the horizon = 10 NM

  13. What am I looking at? • Other vessels less than 10 NM away • Land can be farther than the 10 NM • Depending on Elevation • Weather fronts can be seen beyond the horizon • Sea return will be strongest around your vessel • The top of the Radar is normally the bow of the boat. • It is possible to use true north up (More later)

  14. What am I looking at? • Display often has fuzzy appearance of contacts • Navigation Aids look like vessels • Contacts may appear and disappear • Things close to each other tend combine

  15. Controls and Functions

  16. Control and Functions • Radar Scans 360 degrees about 24 times per minute • It sends pulses of energy then listens for the echo • About 3,000 times per second • 4,320,000 pulses per minute

  17. Control and Functions • Be Careful: • Some of the controls impact the sensitivity of the received signal • Some controls change the display so that it is difficult to see contacts

  18. Control and Functions • Tuning – Adjustment of receiver to transmitted frequency • Gain – Sensitivity of receiver • STC – Suppressing Sea Clutter • Reduces gain near vessel • A/C Rain – Cuts down on rain return • Masks small object • FTC – Suppresses rain clutter from heavy storms • Masks small object

  19. Control and Functions • VRM – Variable Range Mark • ELB – Electronic Bearing Line • Brill and Tone – Back light and Contrast • Trail – leaves the last return(s) dimmer for the next • Rings – Turns range rings on and off • Off Ctr – Moves vessel to display more information • Shift forward to see aft more or aft to see forward more • Also allows other vessel positions on display

  20. Control and Functions • Tuning – Use Automatic • Gain – Automatic • or on highest range adjust manually to just see the noise • Be careful with STC, A/C Rain, and FTC • They can reduce a targets visibility • STC – Keep off or as low as possible • A/C Rain – Keep off unless needed to see through rain • Contact may still be hidden by rain • FTC – Keep off unless needed to see through a storm • Contact may still be hidden by storm

  21. Control and Functions • VRM – Use to track contacts • ELB – Use to track contacts & Identify ZERO BEARING Contacts • Brill and Tone – Adjust to best see the display in present lighting • Trail – Can help in a congested area to sense where targets are headed • Rings – Rings are useful and should be on • Off Ctr – Off for sailboats, on for high speed power

  22. TypicalDisplay

  23. Use of controls - Range • When off shore, 8 nm may be best range setting • No More than 10 nm for base, if available • Change Range several times per hour to all ranges down to one mile. (Lower the range, the larger the target) • Expand the range out to the highest range to look for storm fronts • Should not be left on 8 nm all the time. • Contacts may appear very small and be missed • Plastic and Wood Boats make Poor Targets

  24. Use of controls - Range • When near land set range only high enough to see the land • 3 miles off shore, use 3 mile range as base • When coming into a busy harbor use ½ to 1 nm so contacts are easily detected

  25. Contacts Size • The size of a contact is dependent on: • Range setting • Gain setting • Trail on or off • Type of material for contact • Metal is better than plastic • Anti Sea and rain settings will reduce size of target

  26. Selecting a Range • Need to have response time to correct coarse • Need to be on low enough range to see contact • Recreational vessels can be hard to see and move fast If We Assuming Target Traveling at 25NM/hour

  27. Typical Ranges Full Scale Time to Target* Full Scale Time to Target* • 0.125 0.3 minutes • 0.25 0.6 minutes • 0.5 1.2 minutes • 0.75 1.8 minutes • 1.0 2.4 minutes • 1.5 3.6 minutes • 2.0 4.8 minutes • 3.0 7.2 minutes • 4.0 9.6 minutes • 6.0 14.4 minutes • 8.0 19.2 minutes • 12.0 N/A • 16.0 N/A • 24.0 N/A • 36.0 N/A * Target at 25nm/hour

  28. Range Prospective – 12 miles 000/360 Identify the contacts? 3 270 90 6 12 9 180

  29. Range Prospective – 6 miles 2 4 6

  30. Range Prospective – 3 miles 1 2 3

  31. Our Small Boats • Maneuver quickly so less time is needed • Most important is seeing the target • Even if you have only 7 minutes you can get out of the way • @ 5 knots for 7 minutes you can travel 233 yards. • Or ~700 feet – That would be a real wide ship!

  32. Contact Avoidance with Radar

  33. Contact Avoidance with Radar • When visibility is restricted because of fog, darkness, etc. • Radar can help you get through safely. • Tracking a contact(s) know the Closest Point of Approach • CPA(s) • Priority - Make sure the bearing is changing • Great Cockpit Calculation – 3 minute rule

  34. 3 Minute Rule Speed in knots, add two zeros * = the Distance in yards that will travel in 3 minutes Case 1: Traveling at 5 nm/hr So 5 +00 = 500 yards/3 minutes Since 2000 yards = 1nm, We travel at 4 * 3 = 12 minutes/nm Case 2: Own ship 5 knots with other vessel coming head on at 15 knots 5 miles away! Solution: 5+15 = 20 nm = 2000 yards /3 minutes. So we will meet the other vessel in: 3X5 or 15 minutes * Really Multiplying speed times 100

  35. Relative Bearing vs True Bearing • On Radar you are normally heading up. • Relative Bearing (RB) • Preferred mode for Recreational boats • Corresponds to what you are looking at. • Possible to use a compass input • Allows for True Bearing at top of display • True bearing has the advantage of reducing contact(s) movement as a result of own vessel heading shifting • but can be confusing when single handing

  36. Relative Vs True Bearing • Relative Bearing: Heading shifts on own boat results in contact apparent shifts. • True Bearing: Not as intuitive as to were contacts are relative to where you are going. 090 000

  37. Relative Motion • The contact’s (RB) relative motion is: • The addition of the direction of the contact and your direction over the water • Speed of the contact is also an addition of the two speeds • It is actually the vector sum of the two motions.

  38. Relative Motion on a Radar What is the contacts actual speed and direction? Contact Relative 5nm VL Own Ship 10nm VL

  39. Relative Motion on a Radar What is the contacts actual speed and direction? Add the contacts vector to yours Contact Relative 5nm VL Own Ship 10nm VL

  40. Relative Motion on a Radar What is the contacts actual speed and direction? Contacts true speed and direction is the remaining vector Contact Relative 5nm VL Own Ship 10nm VL

  41. Relative Motion on a Radar 5kns W Nav Aid 5knts 5kns N Relative Motion On Radar 5kns N

  42. Relative Motion on a Radar What will Each see On their Radar? V1 000o at 8 knots V1 360o at 8 knots V2 000o at 15 knots V2 000o at 15 knots Relative motion of V2 (with respect to V1) Is at 150o now moving CCW at 7 knots (Being Overtaken) Relative motion of V2 (with respect to V1) Is at 150o now moving CCW at 23 knots Relative motion of V1 (with respect to V2) Is at 320o now moving CCW at -7 knots (Overtaking) Relative motion of V1 (with respect to V2) Is at 320o now moving CCW at 23 knots

  43. Fast way to find CPA • If you have a glass screen A grease pencil is great • A small clear straight edge is handy P2 = 10:30 P1 = 10:00 4 8 12

  44. Fast way to find CPA P2 = 10:30 CPA P1 = 10:00 4 8 12

  45. Fast way to find CPA Where is the CPA? P1 = 10:00 P2 = 10:30 4 8 12

  46. Fast way to find CPA P1 = 10:00 P2 = 10:30 CPA 4 8 12

  47. Calculate Relative Speed • Measure distance between P1 & p2 • Check against rings • Speed = D/t in hours • 4nm/0.5 hours = 8nm/hr • Measure Distance to CPA = 7 nm • Calculate Time to CPA • T = (D/speed X 60 + P2) • 7/8 X 60 + 10:30 • ~11:22 Relative Speed P1 = 10:00 P2 = 10:30 Cockpit Calc 8nm = 800yrds 3 minutes 2.5 periods/nm = 7.5 min/nm 7 miles = 7 X 7.5 7X7 =49 & 7X8 = 56 So it is = 52.5 minutes to CPA Or about 11:22 CPA 4 8 12

  48. What is Wrong? 9.5NM @ 315o 12NM @043o 7.8NM @315o 8.8NM @ 043o 4 8 12 8.5NM @ 129o 12NM @ 129o 7.6NM@ 201o 11.7NM @ 201o

  49. Contacts all on Collision Course Constant Bearing Rates! 9.5NM @ 315o 12NM @043o 7.8NM @315o 8.8NM @ 043o 4 8 12 8.5NM @ 129o 12NM @ 129o 7.6NM@ 201o Means: Collision! Requires Action! 11.7NM @ 201o

  50. If We Slow or Stop Pass in front! 9.5NM @ 315o 12NM @043o 7.8NM @315o 8.8NM @ 043o 4 8 12 8.5NM @ 129o 12NM @ 129o 7.6NM@ 201o 11.7NM @ 201o

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