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Modems

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Cannot just say 'modem translates between analog and digital' (For ... Needs wire to serial port (adds to wiring clutter) Needs electrical power. Modem Forms ... – PowerPoint PPT presentation

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Title: Modems


1
Modems
  • Problem
  • Computer is digital
  • Telephone line is analog
  • Need translation device called a modem

Analog Signal
Digital Signal
Modem
2
Modems
  • Note
  • Device is digitalTransmission line is analog
  • Cannot just say modem translates between analog
    and digital (For analog device and digital
    transmission line, need something else)

Digital Device
Analog Transmission Line
3
Modulation
  • A Modem is a Modulator and Demodulator
  • Modulation is converting outgoing digital device
    signals into analog transmission line signals
  • Demodulation is converting incoming analog
    transmission line signals into digital device
    signals

Analog Signal
Digital Signal
Modem
4
Modulation
  • Example Frequency Modulation
  • 1 is a high-frequency vibration
  • 0 is a low-frequency vibration

0
1
1
1
5
Modem Forms
  • Internal Modem
  • On printed circuit board inside PC
  • Does not take up desktop space
  • Can be complex to install--must open up computer

6
Modem Forms
  • External Modem
  • Easy to install (just plug into serial port)
  • Takes up desk space
  • Needs wire to serial port (adds to wiring
    clutter)
  • Needs electrical power

7
Modem Forms
  • PC Card Modems
  • Fit in PC Card slots on notebooks
  • Easy to install
  • Do not take up desktop space
  • Expensive
  • Few desktop PCs have PC Card slots

8
Modem Connection for Internal Modem
Phone Line to Wall Jack
Phone Line to Telephone
9
Modem Connection for External Modem
Serial Cable to Serial Port
Phone Line to Wall Jack
Phone Line to Telephone
Wall Power usually uses brick transformer
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