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GPS — Navigation B — Instruments, Mashit 30

11 questions on GPS, from the Navigation B — Instruments exam of Mashit 30. Initialising, controls, accuracy and speed over ground. Every question is shown with its correct answer, as in the official question pool.

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Questions on GPS

  1. How does a GPS receiver work out its position? It receives the identification code and range of 3 or more satellites, and converts the point where the ranges meet into the intersection of a meridian and a parallel on a chart or other display.
  2. What do the initials GPS stand for? Global Positioning System.
  3. The difference between SET UP and INITIALISATION is: All of the above.
  4. What is the difference between the MOB key and the MARK key? MOB marks the present position as an 'active waypoint' and shows the bearing and range to it continuously, while MARK only marks the present position.
  5. To get a position from GPS (Global Positioning System) you need: Simultaneous reception of at least 3 satellites.
  6. Where is it recommended to fit the GPS antenna on board? As low as possible (to reduce its movement), while keeping a clear view of the sky all round.
  7. The loss of position accuracy caused by receiving satellites that are close together is indicated by: Position dilution of precision (PDOP).
  8. Various systems can improve GPS accuracy to a fraction of a metre. How will you know whether they are available to you, or at least how accurate your receiver is? With the vessel moored alongside, compare a fix from 3 crossed bearings with the position the GPS gives, and check that the GPS shows zero speed.
  9. What is the difference between the MOB key and the MARK key? MOB marks the present position as an 'active waypoint' and shows the bearing and range to it continuously, while MARK only marks the present position.
  10. On a GPS receiver, what do the following mean, in order: 1 – ROUTE, 2 – TRACK, 3 – Course To Steer? 1 – several legs on different courses, each between two adjacent, consecutive points, linked into one route and stored in memory under a chosen name; 2 – the path the vessel is meant to follow between the point of departure and the destination; 3 – the course, corrected by the receiver, that must be steered to reach the selected waypoint.
  11. Can a GPS measure speed? Yes.

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