21
Test Result
Possible Cause of Result
FAIL or PASS*
• Patch cord impedance not 100 ohms
• Patch cord mishandling causes changes in impedance
• Installation practices (untwists or kinks of cable -
the original twists should be maintained as much as
possible for each wire pair)
• Excessive amount of cable jammed into the Telecom
Outlet box
• Bad connector
• Cable impedance not uniform
• Cable not 100 ohm
• Impedance mismatch at junction between patch cable
and horizontal cable
• Poorly matched plug and jack
• Use of 120 ohm cable
• Service loops in telecommunications closet
• Inappropriate autotest selected
• Defective link adapter
Unexpected PASS
• Knots or kinks do not always cause return loss
failures, especially on good cable and far removed from
the ends of the link
• Incorrect autotest selected (easier to pass RL limits)
• “FAILs” at low frequency on RL graph but passes overall.
Due to the 3 dB rule, whereby all RL results measured
while insertion loss <3 dB cannot fail
Return Loss
