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How is amplitude modulation achieved?
  • A
    The information is added onto the carrier wave by altering the amplitude of the carrier.
  • B
    The information is added onto the carrier wave by interrupting the carrier.
  • C
    The information is added onto the carrier wave by reversing the phases of the carrier.
  • D
    The information is added onto the carrier wave by altering the frequency of the carrier.

Refer to figure.
Learning Objective 062.01.01.06.01: Define ‘amplitude modulation’: the information that is impressed onto the carrier wave by altering the amplitude of the carrier.


When we want to send information via radio waves, we have to modulate the carrier wave somehow, this is the process of adding information to it. There are a few ways to do this. In the early days of radio, it was done by sending pulses of the carrier wave as morse code, pulse modulation. These days we can modulate the amplitude of the carrier wave, to carry our information, or we can modulate the frequency slightly, to carry information also.

Amplitude Modulation (AM) is shown in the annex above, which is the easiest to get an understanding of how modulation works. We "overlay" an information wave on top of the carrier wave, so the information is carried without needing another transmission, and then the carrier wave is just removed in the receiver, but the information remains intact. AM is quite sensitive to noise (hisses and crackles) and it also produces two "side bands" of information, one wave at the top, on at the bottom, of which one can be removed to save on power and bandwidth, as is done with HF communications in aviation.

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