IDEAL INDUSTRIES LANTEK 6 Basic, Руководство пользователя

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Chapter 3
Structured Cable Field Calibration and Testing
3-27
Troubleshooting Attenuation Problems
Problem: High Attenuation Reading
Probable Causes Poor connector termination points.
Excessive cable length.
Incorrect or poor quality adapter cable.
Incorrect cable.
Other Tests Affected Test Possible Result
DC Loop Resistance May be high.
Capacitance May be high.
Length May be over limit.
NEXT May be low on pair combinations.
Average Impedance May be low.
Return Loss
May be over limit.
Return Loss Test
This test measures the ratio of reflected to transmitted signal strength. Good quality
cable runs will have little reflected signal, indicating good impedance matches in the
run’s various components.
Figure 3-17: Return Loss Test Screen
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.
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