Chapter 7
Cable Testing Fundamentals
7-23
Impedance Errors
Impedance errors cause signal reflection and strength reduction. Average
impedance of each pair should be equal to the LAN system impedance of 100, 120,
or 150 Ω, plus or minus 15 Ω.
Troubleshooting Impedance Problems
Problem: High Impedance Readings
Probable Causes Compression, stretching, or excessive bending damage to
the cable.
Defective connectors.
Insulation damage at a connector.
Ground loops created between cable shielding (if used) and
equipment grounding (via RS-232 cable to computer, or
auxiliary power).
Improperly chosen cables or patch cords.
Moisture in the cable.
Other Tests Affected Test Possible Result
Length Affected pairs will appear longer.
Average Impedance Change in average impedance is
inversely proportional to change in
capacitance.
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