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Electronics

Amplitude (AM) and frequency modulation (FM) techniques

  • 5 things to know
  • Paper 3, section B

Overview

Modulating a carrier by amplitude or frequency, the bandwidth each needs, and reading the waveforms.

What you need to know

Answer each one before you reveal it.

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Numbers

What is bandwidth, how is AM bandwidth calculated, and what is it when fₘ = 9900 Hz?

Numbers

What does Δf represent, and why does FM need more bandwidth than AM?

Key term

How is the carrier frequency read from an FM waveform, what do its compressed and expanded regions show, and how is the information frequency found?

Process

How does available bandwidth affect the data capacity of a channel?

Key term

Which transmission medium offers the greatest available bandwidth?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is modulation in the context of signal transmission?

    Model answer

    Modulation is the process of varying a property of a carrier wave in accordance with an information signal to enable transmission of information.

  2. 2

    Define bandwidth as it applies to a modulated signal.

    Model answer

    Bandwidth is the range of frequencies occupied by a modulated signal.

  3. 3

    What is a carrier wave?

    Model answer

    A carrier wave is a high-frequency electromagnetic wave that is modulated to carry information.

  4. 4

    What is meant by an information signal in communication systems?

    Model answer

    An information signal is the lower-frequency signal containing the data or audio to be transmitted.

  5. 5

    Explain how amplitude modulation works in terms of what happens to the carrier wave.

    Model answer

    In amplitude modulation, the amplitude of the carrier wave is varied in proportion to the instantaneous value of the information signal while the frequency remains constant.

  6. 6

    Which property of the carrier wave remains unchanged during amplitude modulation?

    Model answer

    The frequency of the carrier wave remains constant during amplitude modulation.

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