Chapter 7
Cable Testing Fundamentals
7-21
Return Loss Errors
Like attenuation, excessive return loss reduces signal strength at the receive end. It
also indicates a mismatched impedance at some point along the cable run. A value
of 20 dB or greater indicates a good twisted pair cable. A value of 10 dB or less is
severe, and causes a large reflection of signal back to the source.
Troubleshooting Return Loss Problems
Problem: Excessive Return Loss (Value of 10 dB or less)
Probable Causes Open, shorted, or damaged cable.
Installed cable, cable segments, or patch cord have improper
characteristics.
Damaged or worn cable or connectors.
Poor punch-down.
Factory splice in cable.
Other Tests Affected Test Possible Result
Attenuation May be high.
Capacitance and
Average Impedance Could be affected if the impedance
mismatch is caused by cable
damage.
DC Loop Resistance May be high if due to a poor
punch-down.
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