Diagnosing Twisted Pair Cabling Faults
Common Causes of Twisted Pair Test Failures 4
4-5
Table 4-1. Diagnosing Twisted Pair Test Failures (cont.)
NEXT passes, but the plot shows that measurements exceed the limit
For ISO/IEC standards, NEXT is not evaluated where insertion loss is less than 4 dB (the 4 dB rule).
Return passes, but the plot shows that measurements exceed the limit
Return loss is not evaluated where insertion loss is less than 3 dB (the 3 dB rule).
Return loss gives FAIL, FAIL*, or PASS* result
• Patch cord or cable impedance not 100 Ω
• Patch cord handling causing changes in impedance
• Excessive amount of cable jammed into outlet box
• Tight service loops in telecommunications closet
• Excessive untwisting of pairs at connector
• Poor quality connectors
• Cable impedance not uniform (poor quality cable)
-continued-
To Next Page
Loading...
