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Subel. G
6 questions
Subelement G

VHF-DSC Equipment & Communications:

Section 50

VHF Channel System

A VHF frequency channel pair of TX 157.200 MHz and RX 161.800 MHz would most likely be:

  • A VTS frequency for VTS - Ship communications.
  • A simplex Public Correspondence Coast Radio Station frequency.
  • A simplex Private Coast Radio Station frequency.
  • Correct Answer
    A duplex Public Correspondence Coast Radio Station frequency.

A VHF frequency channel pair of TX 157.200 MHz and RX 161.800 MHz would most likely be:

(D). A duplex Public Correspondence Coast Radio Station frequency.

Channel 24 TX 157.200 MHz and RX 161.800 MHz (Duplex) for Public Correspondence (Marine Operator) used for VDSMS, VHF Digital Small Message Services.

TX and RX stand for Transmit and Receive

For more info, please see US Coast Guard's Int. VHF Marine Radio Channels and Frequencies

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Which channel is utilized for the required Bridge-to-Bridge watch?

  • Correct Answer
    VHF-FM on Ch-13 in most areas of the continental United States.
  • DSC on Ch-70
  • VHF-FM on Ch-16
  • The vessel's VHF working frequency.

Which channel is utilized for the required Bridge-to-Bridge watch?

(A). VHF-FM on Ch-13 in most areas of the continental United States.

47 CFR § 80.331 - Bridge-to-bridge communication The communication need to include the name of the vessel, position, course, and speed.

Bridge-to-bridge communication requirements

The communication occurs on VHF-FM Channel 13, which is 156.650 MHz, and is normally limited to 1 watt.
Wikipedia Marine VHF Radio, please see the frequency table

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While conducting routine communications using the wheelhouse VHF with a station 1 mile distant, your recommended power setting would be:

  • 25 watts after dark.
  • Correct Answer
    1 watt, day or night.
  • 25 watts during a clear sunny day.
  • 1 watt using DSC at night.

While conducting routine communications using the wheelhouse VHF with a station 1 mile distant, your recommended power setting would be:

(B). 1 watt, day or night.

Normally, the transmissions are limited to 1 watt.

The communication occurs on VHF-FM Channel 13, which is 156.650 MHz, and is normally limited to 1 watt.
Wikipedia Marine VHF Radio, please see the frequency table

§ 80.331 Bridge-to-bridge communication procedure.

(c) Use of power greater than 1 watt in a bridge-to-bridge station shall be limited to the following three situations:

  • Emergency.

  • Failure of the vessel being called to respond to a second call at low power.

  • A broadcast call as in paragraph (a)(1) of this section in a blind situation, e.g., rounding a bend in a river.

For details of regulations, please see 80.331 here

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The USA-INT control on VHF units:

  • Selects duplex operations for U.S. coastal waters and simplex operations in non-U.S. waters, on the "alpha" channels.
  • Ensures that the “alpha” channels are correctly set to duplex for use in U.S. waters & on VTS channels.
  • Correct Answer
    Changes selected international duplex channels to simplex channels for use in U.S. waters, on the "alpha" channels.
  • Changes selected international simplex channels to duplex channels for use in U.S. waters, on the "alpha" channels.

The USA-INT control on VHF units:

(C). Changes selected international duplex channels to simplex channels for use in U.S. waters, on the "alpha" channels.

For marine VHF, the Simplex is used in US coastal waters, where sending and receiving messages occurs on the same channel (frequency)

The International frequencies, per ITU, are Duplex, where sending and receiving is on different frequencies.

Simple explanation of Simplex/Duplex usage

Good info (pdf) on marine VHF use

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The USA-INT control on VHF units:

  • Was made necessary by a desire for more duplex channels in the U.S.
  • Correctly set, will result in duplex operations in U.S. Coastal waters on the "alpha" channels.
  • Correct Answer
    Correctly set, will result in simplex operations in U.S. Coastal waters on the "alpha" channels.
  • Was made necessary by a desire to convert simplex international channels to duplex channels in the U.S.
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Proper and legal VHF operations require all of these EXCEPT?

  • The channel must be designated as valid for the nature or type of communications desired.
  • Simplex, duplex and alpha channel modes must be correctly selected.
  • The power level must be appropriately chosen by the operator.
  • Correct Answer
    The correct bandwidth must be selected by the operator.

Proper and legal VHF operations require all of these except?

(D). The correct bandwidth must be selected by the operator.

The question refers to the proper and legal OPERATIONS. The marine VHF units use channels instead of dialing up frequencies as ham radio amateurs do. This helps to stay legal by not accessing unauthorized frequencies. FCC has a map of what frequencies can be used by whom.

See the table of channels and what frequencies they are assigned to on:

US Coast Guard VHF Channel Table for US

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