Certifying Twisted Pair Cabling
Twisted Pair Autotest Results 3
3-15
Resistance
Resistance results show the dc loop resistance for each
cable pair. The smart remote shorts the end of each pair
to create the loops. A pair’s resistance depends on the
integrity of the contacts in the connector, the length of
the pair, and its wire gauge.
Resistance problems always affect other tests. For
example:
• A link that is too long has higher-than-normal
resistance and will fail the length test.
• High-resistance connections reflect signals that cause
the return loss test to fail. The tester’s HDTDR test
tells you the distance to the bad connection.
Most standards do not have a limit for resistance. The
tester shows an
i when no limit is available. Figure 3-9
shows the resistance results screen.
amd85f.eps
Figure 3-9. Resistance Results
Characteristic Impedance
Note
Most test limits do not require the characteristic
impedance measurement. Characteristic
impedance is not displayed for these limits.
Impedance measurements require a cable at
least 5 m (16 ft) long. Cables shorter than this
length will always pass the impedance test.
Characteristic impedance results show approximate
characteristic impedance of each cable pair.
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