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Subelement C
Equipment Operations
Section 13
VHF Equipment Controls
What is the purpose of the INT-USA control settings on a VHF?
  • To change all VTS frequencies to Duplex so all vessels can receive maneuvering orders.
  • To change all VHF channels from Duplex to Simplex while in U.S. waters.
  • Correct Answer
    To change certain International Duplex channel assignments to simplex in the U.S. for VTS and other purposes.
  • To change to NOAA weather channels and receive weather broadcasts while in the U.S.

The goal is to inform all vessels to be able to receive maneuvering orders.

In US waters, change all VHF channels from Duplex to Simplex while in U.S. waters.

In International waters, reverse. Change all VTS frequencies to Duplex so all vessels can hear the orders.

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VHF ship station transmitters must have the capability of reducing carrier power to:
  • Correct Answer
    1 watt.
  • 10 watts.
  • 25 watts.
  • 50 watts.

§ 47 CFR 80.215 Transmitter power.
(e)Ship stations frequencies above 27500 kHz. The maximum power must not exceed the values listed below.

(1) Ship stations 156-162 MHz - 25W *

* Reducible to 1 watt or less, except for transmitters limited to public correspondence channels and used in an automated system.

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The Dual Watch (DW) function is used to:
  • Listen to Ch-70 at the same time while monitoring Ch-16.
  • Sequentially monitor 4 different channels.
  • Sequentially monitoring all VHF channels.
  • Correct Answer
    Listen on any selected channel while periodically monitoring Ch-16.

Dual watch is a setting which allows listening on multiple frequencies at once. Most units will require that one of the dual watch channels is 16.

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Which of the following statements best describes the correct setting for manual adjustment of the squelch control?
  • Correct Answer
    Adjust squelch control to the minimum level necessary to barely suppress any background noise.
  • Always adjust squelch control to its maximum level.
  • Always adjust squelch control to its minimum level.
  • Adjust squelch control to approximately twice the minimum level necessary to barely suppress any background noise.

Squelch is a setting which filters out background noise being received.

Squelch is turned down such that the background noise is just audible, and then down one additional level.

But you can have too much of a good thing, and if you increase squelch, you will blank out receiving some transmission. Same works for hand-helds and CB radios.

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The “Scan” function is used to:
  • Monitor Ch-16 continuously and switching to either Ch-70 or Ch-13 every 5 seconds.
  • Scan Ch-16 for Distress calls.
  • Scan Ch-70 for Distress alerts.
  • Correct Answer
    Sequentially scan all or selected channels.

Scan is a function which searches through multiple frequencies listening for transmissions.

It is a marine radio function which you must select. Also, must set frequencies (channels) to scan.

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Why must all VHF Distress, Urgency and Safety communications (as well as VTS traffic calls) be performed in Simplex operating mode?
  • To minimize interference from vessels engaged in routine communications.
  • Correct Answer
    To ensure that vessels not directly participating in the communications can hear both sides of the radio exchange.
  • To enable an RCC or Coast station to only hear communications from the vessel actually in distress.
  • To allow an RCC or Coast station to determine which transmissions are from other vessels and which transmissions are from the vessel actually in distress.

Two objectives:

  1. To reduce signals from vessels in the range talking to each other.

  2. In Simplex, other ships can hear both sides of communications.

When operating in Simplex, the transmitting and received signals are sent on the same frequency. Therefore, only one side of the conversation can occur at a time.

Any 3rd party people tuned into the channel will be able to hear the entire conversation, as opposed to in Duplex. In Duplex, Transmit and Received signals occur on two separate frequencies, and a 3rd party may only be tuned into one of them. This will only allow them to hear half of the conversation.

For a great overall info on communications in pdf format, this will be a great reference document to download:

Principles of Maritime Mobile Service

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