Analog Versus Digital Communications

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Analog Versus Digital Communications
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Analog Versus Digital Communications

• Chapter 5 Objectives after reading this chapter
  and completing the questions, you will be able
  to
• Explain what analog communications means
• Discuss the differences between analog and
  digital communications
• Describe the process of carrying the analog
  signal
• Explain impairments in the analog transmission
• Converse fluently about the use of digital
  transmission systems in the telephone hierarchy
• Describe the way we regenerate the digital signal
  in the link

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Analog Transmission Systems

• Definitions
• digital
• analog
• Analog Transmission Systems

Fig. 5-1 Using an oscilloscope, see the
characteristics of an analog signal.
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Analog Transmission Systems

• Comparing analog wave to how the beat of the
  music changes lights in a DJs equipment.
  Compression and rarefaction.

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Sine wave

• Sinusoidal wave, 360 degrees
• Electrical current around a magnetic force

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Human Voice

• Usable information in range 300 to 3,300 Hz

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Band Limits

• 4-kHz bands
• Radio or wires
• Band pass filters

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Band-limited channel

• See Chapter 2, page 27
• Band pass filters separate the channels

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Attenuation

• Signal diminishes in amplitude
• Amplifiers

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Amplifying the signal

• Spaced 15,000 to 18,000 apart
• Attenuation and noise
• Resistance
• White noise line loss, frayed wires, lightning,
  inductance, heat, etc.

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Amplifiers and noise in analog circuits

• Both the telephone signal and the noise are
  amplified

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Analog-to-Digital Conversion

• A/D converter
• Sampling
• Nyquist theorem

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Digital Repeaters

• Remove analog equipment
• Amplifiers, load coils
• Insert repeaters approximately each mile

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Digital Signaling

• Unipolar signal
• Bit time
• Alternate mark inversion (AMI)
• Why digital? Quality is the reason.

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Amplitude Control

• Pads vs. signal strength

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Repeaters

• Regenerative repeaters discriminate between
  noise and signal, recreate the message

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Analog Versus Digital Quality

• Deliver to the receiver a signal identical to
  what was inserted at the transmitter

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Digital Data in an Analog World

• Digital-to-analog conversion, Modem four D/A
  conversions!!
• Most voice and data transmission systems use
  digital technology
• Local loop as it was
• Held everything back