Principles of Communications:
Subelement B
Section 9
Modulation, Demodulation, AM, FM
What statement best describes modulation?
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Correct AnswerImposing intelligence onto a radio carrier signal.
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Changing mark-space to 1 and 0.
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Adjusting the frequency to the optimum band for long distance communications.
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Converting the carrier from a low frequency to a higher frequency.
Modulation is an (A). Imposing intelligence onto a radio carrier signal.
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.
Great article from Encyclopedia Britannica Modulation and Demodulation
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What statement best describes demodulation?
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Detuning the receiver to remove interfering signals.
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Correct AnswerExtracting intelligence from the radio carrier signal.
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Removing atmospheric noise from the signal.
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Separating the TELEX signals from the voice signals.
Demodulation is (B) Extracting intelligence from the radio carrier signal.
Naturally opposite process to modulation, which adds data, voice, music, etc. to radio carrier frequency, the demodulation suppressed the carrier frequency and only produces the original data, voice, or music and sends it to an output device such as a speaker or sends it to another process.
The demodulation process occurs inside the receiver device, such as a radio, or could be a SDR, software defined radio.
See Wikipedia article Demodulation
Great article from Encyclopedia Britannica Modulation and Demodulation
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Which statement best describes amplitude modulation?
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The character data from the terminal is changed to audio tones.
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The frequency is varied in synchronization with the modulating signal.
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Correct AnswerThe amplitudes in the sideband(s) changes but the radio carrier frequency remains constant.
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The amplitude of the carrier is changed but there is still only a single frequency being transmitted.
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The emission designation for MF-HF voice signals is (D). J3E.
J3E is used by by vessels, planes, and ham amateurs, to transmit voice messages.
J is defined as a SSB with suppressed carrier
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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Which statement best describes frequency modulation?
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Correct AnswerThe information signal changes the radio carrier frequency but the amplitude remains constant.
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Both the amplitude and frequency are changed by the modulating signal.
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Frequency modulation is subject to interference by atmospheric noise.
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High level mixing of the final amplifier signal and the information signal.
Modulation is (A). The information signal changes the radio carrier frequency but the amplitude remains constant.
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
Last edited by markadlerdallas. Register to edit
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Emission designation for VHF-FM (B) F3E
F3E is used by marine radios in the FM mode for voice messages.
F is Frequency Modulation, FM
3 is defined as a single channel designated for analog info
E is defined for voice or music, not data for processing.human)
For more details, see Wikipedia article called
Types of Radio Transmissions
Last edited by markadlerdallas. Register to edit
Tags: none
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