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Radio communications — Navigation B — Instruments, Mashit 30

50 questions on radio communications, from the Navigation B — Instruments exam of Mashit 30. VHF, channels, antennas, DSC and calling procedures. Every question is shown with its correct answer, as in the official question pool.

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Questions on Radio communications

  1. What is a vessel's MMSI? All of the above.
  2. What is the electronic unit known as DSC? A unit built into radios that encodes and decodes messages in digital communication.
  3. Why do you need the appropriate class of radio operator's certificate to use radio equipment for international communications? Because not knowing the procedures and what the controls do could stop you getting help in distress, or could interfere with other vessels' rescue communications.
  4. What does the DUAL WATCH (DW) control on a VHF radio do? You listen and transmit on the selected channel, but reception switches to channel 16 whenever there is traffic on it.
  5. You are handling distress traffic on channel 16 and, because of constant interference, you want to move to a 'clear' channel. Which group of channels is suitable? 06, 08, 13.
  6. What do the squelch on a VHF radio, the anti-clutter controls on a radar, hand steering and correct sail trim have in common? All of the above.
  7. What mainly affects communication range on VHF? A clear path between the antennas, transmitter power, the height of the antennas and radio propagation conditions.
  8. When a distress incident is over and channel 16 is to be released for normal calls, how does the station controlling the distress traffic announce it? SEELONCE FEENEE.
  9. Which transmissions are made on low power? All of the above.
  10. How often is a NAVTEX broadcast received from a given coast station? Every 4 hours.
  11. You have called a coast station and there is no answer. What do you do? I wait at least two minutes and call it again on its calling channel or its working channel, after making sure the channel is clear.
  12. Can two Israeli yachts talk to each other on channel 26? No, channel 26 is a duplex channel for public correspondence.
  13. What is VHF channel 6 used for? Communication between vessels.
  14. What should you set up on the NAVTEX receiver before sailing? The "stations" and the types of message you want.
  15. What is required of a VHF radio's antenna? Its length must suit the radio's transmitting and receiving frequency band.
  16. What is the main factor that determines transmission range on VHF? Line of sight between the antennas.
  17. Distress messages that appear in the output of a NAVTEX receiver: Come from coast stations and the regional administration of the NAVTEX transmitter, to increase the number of vessels that can give help.
  18. VITAL, IMPORTANT and ROUTINE are: The grades that classify NAVTEX messages by priority and content.
  19. What is meant by "Digital Selective Calling"? The device or system whose purpose is to identify others and itself, and to decode and process messages for digital communication = Digital Selective Calling.
  20. The identification of a vessel's radio station in international communication: Answers b and c are correct.
  21. When vessels are required to carry a VHF radio, this means a radio that receives and transmits between 156 and 174 MHz. Why? Because this is the band allocated to the maritime mobile service by the international telecommunications organisation.
  22. For which purposes have no channels been allocated in the marine VHF band? Monitoring vessels at anchor, an automatic alarm when the radar detects a close approach, automatic dialling through a satellite relay.
  23. Switching to which channels, and for what reason, will cause voice contact between two vessels to be lost? Choose the answer that is not correct. Channel 13, because it is meant for "bridge-to-bridge" contact between large ships, whose antennas are higher than those of smaller vessels.
  24. A station controlling distress traffic wants to stop interference on channel 16 from stations that are unaware of the situation. It will tell them: SEELONCE MAYDAY.
  25. A station that is not controlling the distress traffic, but is in the area of a distress incident, wants to stop interference on channel 16 from stations unaware of the situation. What will it say? SEELONCE DISTRESS.
  26. When a distress incident is nearly over and channel 16 is no longer needed continuously (a "careful ending"), the station controlling the traffic will announce: PRUDONCE.
  27. Which checks of a vessel's radio equipment must be carried out and recorded in the ship's log? Answers a and b (if such a log exists) are correct.
  28. Which of the following identifies a ship? 232000432
  29. What does the physical size of an antenna depend on? The higher the frequency, the smaller the antenna can be.
  30. In FM modulation: The frequency of the carrier wave is varied according to the information transmitted.
  31. What is the DUAL WATCH button on a VHF radio used for? The radio listens on channel 16 and one other selected channel.
  32. On which frequency band does a NAVTEX receiver receive? MF.
  33. What do VITAL, IMPORTANT and ROUTINE messages refer to, and what do they mean? The grades that classify NAVTEX messages by priority and content.
  34. Can two yachts talk to each other on VHF channel 25? No – it is a duplex channel.
  35. When will you choose to transmit in simplex, and when in duplex, on a marine VHF radio? We cannot choose; the radio switches between them automatically when the channel is changed.
  36. Why is it sometimes necessary to change the transmitting frequency at night when setting up HF communication? Because the height of the ionosphere changes.
  37. What is the frequency range of a marine VHF radio? Between 156 MHz and 174 MHz.
  38. A (portable) VHF transmitter can reduce its transmitting power down to: 1 W.
  39. What is the purpose of AIS? To improve safety of navigation and prevent collisions between vessels.
  40. What does the code MA33 indicate? The identification code of a NAVTEX message.
  41. How many times, and for how long each time, does a NAVTEX station transmit in one day? Every 4 hours, for at most 10 minutes each time.
  42. Which checks must be carried out on a vessel's radio equipment? Answers a and b (if such a log exists) are correct.
  43. What is the number 428000500? Answers a and b are correct.
  44. Which DSC data is sent automatically with every transmission? MMSI.
  45. Which messages can be transmitted from the vessel on a NAVTEX set? None of the above.
  46. How are messages delivered in the NAVTEX system? Through a worldwide network of administrations and transmitters that broadcast safety information to shipping; vessels receive the information in printed form on dedicated receivers called NAVTEX receivers.
  47. How is the chain of NAVTEX transmitters that broadcast safety information laid out? So that within each transmitter's designed range (about 400 miles) there is no interfering overlap with the transmitter covering the neighbouring area (about 800 miles), while neighbouring administrations coordinate power and broadcasts.
  48. How do distress messages appear in the output of a NAVTEX receiver? They come from coast stations and the regional administration of the NAVTEX transmitter, to increase the number of vessels that can give help.
  49. What is the electronic unit known as DSC? A unit built into radios that encodes and decodes messages in digital communication, designed so that it does not depend on the operator's skills.
  50. What mainly affects communication range on VHF? A clear path between the antennas (antenna height), transmitter power, antenna gain and matching, and a number of radio-wave propagation conditions.

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