(D). The carrier is a Radio Frequency (RF) signal that is modulated to carry intelligence.

Disturbing the carrier (hum) signal (frequency) is modulation. This can be done by waves of data, voice, music, etc.

A carrier signal is produced inside of the transmitter by a special component. The signal is a steady hum, having unchanging frequency and unchanging height of waves, also called an amplitude.

The AM modulation modulates the carrier wave to produce above carrier frequency and below sine waves.

The FM modulation changes the frequency of the wave, slowing or speeding the wave cycles.

How Does Modulation Work

Great article from Encyclopedia Britannica Modulation and Demodulation

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J3E emission be used for GMDSS Distress communications
(A). 2182.0 kHz, 16420.0 kHz or 8291.0 kHz.

This is just memorization. Mnemonic: first numbers 2 1 8 2+8=10 first number is second in this series.

For short but excellent explanation, see Blue Seas site, article Distress, Urgency, Safety, & Hailing Frequencies:
First table: Voice Guard Frequencies

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How many sidebands are present in the J3E mode? (B). One upper sideband.

J3E is a SSB, which means that the carrier frequency and one of the sine waves around the carrier frequency is also suppressed.

Usually, it is is the Lower Side Band, leaving the Upper Side Band alone. This channels all effective radiation power in a single band, allowing it to reach much further.

Because of the extended range, the SSB (upper side band) J3E is used by by vessels, planes, and ham amateurs, to transmit voice messages.

J is defined as a SSB with suppressed carrier, lower side band
3 is defined as a single channel designated for analog info
E is defined for voice or music, not data for processing but for human receiver

For more details, see Wikipedia article called Types of Radio Transmissions

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What is the signal transmitted in H3E mode?
(C). A full carrier and the upper sideband.

H is defined as a SSB with full carrier frequency
3 is defined as a single channel designated for analog info
E is defined for voice or music, not data for processing but for human receiver

For short description, please see FCC ID Emissions Designator H3E

For more complete info, please see Wikipedia's article Types of Radio Emissions

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What is the signal transmitted in J2B mode?
(C). An upper sideband of 2 alternating tones.

J is defined as a SSB with suppressed carrier
2 is defined as a single digital channel that uses subcarrier frequency
B is defined for machine decoding in radioteletype and digital modes--an electronic telegraphy.

J2B is a SSB, with subcarrier, which means that the carrier frequency and one of the sine waves around the carrier frequency is also suppressed, usually the Lower Side Band, leaving the Upper Side Band as the SSB.

The subcarrier is an additional frequency. It sends additional information or data.

The two tone in J2B (SSB, w/ subcarrier) means that a non-audible tones will be transmitted. Also, two-tone system is used for testing for a number of errors, especially intermodulation distortion of frequencies.

When two different sine waves are used as input, the transmitter's intermodulation distortion may produce frequencies that are sum and the difference of the originating frequencies.

See Wikipedia article Two Tone Testing

For more details, see Wikipedia article called
Types of Radio Transmissions

For details about Subcarriers, please see Wikipedia: Subcarriers

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NAVTEX is part of the Global Maritime Distress and Safety System (GMDSS) and is used to broadcast Maritime Safety Information (MSI), such as weather warnings and navigational alerts.

While NAVTEX messages in categories A (navigational warnings), B (meteorological warnings), D (search and rescue information), and L (additional navigational warnings) are generally mandatory, a GMDSS Radio Operator may program certain NAVTEX receivers to reject them if the same information is being received through another MSI system (such as satellite-based SafetyNET). This helps prevent redundant messages.

The incorrect choices:

• Some NAVTEX receivers can be programmed to reject mandatory messages if another MSI system provides them, making the first option incorrect.
• SELCAL (Selective Calling) is not used to manually select NAVTEX stations, as they are automatically tuned by frequency and region.
• The "None" option does not allow full rejection of all categories, so the third choice is incorrect.

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