Class Notes

Signal Characterization

TODO

Will rewrite/review

Sources

  1. Signal and Transmission Media Characterization (Lecture Slides)
  2. Class lecture

Signals

  • A signal is a function of a variable(s) that describe a physical/abstract phenomenon.
    • Electrical signals - voltage/current as a function of time. They come from an electricity phenomena.
      • DC Signal
      • AC Signal
        • Periodic and non-periodic
        • Digital and analog (digital must be symmetric when considering magnitude and polarity)
    • Electronic signals - produced/modified using semiconductor/electronic devices.
    • Electromagnetic signals
      • Also known as radio signals
      • Made up of the electric field wave and the magnetic field wave. Electric field is found on the vertical plane, whereas magnetic field is drawn in the horizontal plane.
      • Sinusoidal in form
      • Moves along the z direction
      • Moves well in space/vacuum, as opposed to water or wire where the magnetic field is reduced. In other words, they do not need a physical material to travel, as opposed to electrical signals which depend on electrons to travel.
      • a propagating magnetic field generates an electric field and vice versa
      • They travel perpetually as long as the electric field has enough energy. Nonetheless, as energy travels, their energy diminishes due to attenuation.
      • Light
        • Color is determined by frequency of the sinusoidal components of the electromagnetic signal
        • Red to Violet is the visible spectrum or the range of visible light
  • Analog signals are continuous while digital signals have a discrete amplitude/levels (ideally also discrete in the time domain).
  • Communications that carry voltage or current (communication involving wires) generate unwanted electromagnetic signals. Anything that goes out of the receiver is lost energy while anything that goes out of the wire is a security risk. Anything generated outside of the wire causes interference.
    • FCC certified labels are added to electromagnetic devices to indicate they are able to meet the electromagnetic signal limits set by the FCC (to limit the signals generated by any electromagnetic device/component).
  • Periodic has perfect repetition while non-periodic does not
    • Characteristics of Periodic
      • Amplitude (peak and peak-to-peak)
      • Period - time between repetitions (spans 360 degrees)
      • Frequency - 1/Period
      • Phase angle - angle relative to start
    • Characteristics of Non-Periodic
      • Duration
      • Minimum and maximum amplitude
  • Signal Plots
    • Sine wave in time domain (amplitude and time)
    • Sine wave in frequency domain (amplitude and frequency)
  • Composite signal the sum/combination of multiple periodic signals.
    • A non-periodic signal has infinite number of sine wave components, which can be represented as a distribution in the frequency domain.
    • Two components of a frequency signals can produce an effect when their phase is modified relative to each other.
      • same phase = add two components
      • opposite phase = subtract two components
      • vector addition applies whereby the output signal is the resultant
  • Any digital signal is comprised of multiple sine waves (they are a composite signal).

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