Electromagnetic Signals

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Electromagnetic Signals

• Signals
• Analog (signal intensity varies smoothly over
  time) Analog signals can have any value in a
  range.
• Digital (constant level over time, followed by a
  change to another constant level) Digital signals
  have a limited number of values.

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Analog Signals
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Digital Signals
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Signals - periodicity

• Periodic - consists of continuously repeating
  pattern and completes the pattern within a
  measurable time frame. A sine wave is the
  simplest periodic signal.
• Aperiodic - a signal with no repetitive pattern
  can be decomposed into an infinite number of
  periodic signals

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Periodic Analog Signals

• represented by sine waves

phase difference
1 cycle
amplitude (volts)
time
(sec)
frequency (hertz)
cycles per second
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Units

• Frequency
• Hertz(Hz) 1 Hz
• Kilohertz(KHz) 103
• Megahertz(MHz 106
• Gigahertz(GHz) 109
• Terahertz(THz)1012

• Period
• Second(s) 1 s
• Millisecond(ms)10-3
• Microsecond(us)10-6
• Nanasecond(ns)10-9
• Picosecond(ps)10-12

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Time vs Frequency Plots

• Time Domain Plot - Changes in Amplitude with
  respect to time.
• Frequency Domain Plot shows relationship of
  Maximum amplitude vs frequency

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Time vs Frequency Plots

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Electromagnetic Signals

• Signals are complex
• Spectrum (range of frequencies) -the spectrum of
  a signal is the collection of all the component
  frequencies it contains
• Bandwidth is the width of the frequency spectrum
  (highest frequency-lowest frequency)

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Complex Signals

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Digital Signals

• represented by square waves or pulses

1 cycle
amplitude (volts)
time
(sec)
frequency (hertz)
cycles per second
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Electromagnetic Spectrum for Transmission Media