Crosstalk Issues

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• crosstalk indicates a problem with bad wiring, a bad connector, or improper termination
  • check for:
    • excessive untwisting at the ends
    • kinks or crush points along its run
  • measured in dB
    • higher value = less noise
    • measurements vary according to category and application

Types of Crosstalk

• Near End (NEXT)
  • measures crosstalk on the receive pairs at the transmitter end
  • caused by excessive untwisting of pairs or faulty bonding of shielded elements
• Attenuation to crosstalk ratio, near end (ACRN)
  • the difference between insertion loss and NEXT
  • equivalent to signal to noise ratio (SNR)
  • high value means signal is stronger than noise
  • low value means link is likely subject to high error rates
• Attenuation to crosstalk ratio, far end (ACRF)
  • far-end crosstalk (FEXT) is measured on the receive pairs at the recipient end
  • difference between insertion loss and FEXT
  • measures cable performance regardless of the actual link length
• Power sum
  • confirm that the cable is suitable for this type of application
  • gigabit and 10 GbE use all four pairs
  • measured by energizing 3 of 4 pairs in turn
• Alien crosstalk
  • signal traffic from cables in close proximity that causes interference to another cable
  • caused by:
    • cinching a cable bundle with ties too tightly
    • poorly terminating cabling