Decibel (dB)
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Decibel (dB)

Decibel (dB) - Unit of comparison (Relative)

 A decibel is  unit of comparison, which represents a difference between two values.

• Absolute values are the measurement of what the actual value is:
  • Units of comparison are measurements of change in power.
• Relative values are measurement of what the comparison between two values is:
  • Units of transmit or received power measurements are absolute power measurements.
  • Units of comparison are used to measure how much gain or loss occurs because of the introduction of cabling or an antenna.
  • Units of comparison are used to represent a difference in power from point A to point B.

In wireless networking, decibels are often used either to compare the power of two transmitters or, more often, to compare the difference or loss between the EIRP output of a transmitter’s antenna and the amount of power received by the receiver’s antenna.

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Reference:
Coleman, David D.,Westcott, David A. CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-106 Wiley.