Length - Fluke DTX-1800 Technical Reference Handbook

DTX Series CableAnalyzer
Technical Reference Handbook
Characteristic impedance results show approximate
characteristic impedance of each cable pair.
Characteristic impedance is the impedance a cable would
have if the cable were infinitely long. Proper network
operation depends on constant characteristic impedance
throughout the system's cables and connectors. Abrupt
changes in characteristic impedance, called anomalies,
cause signal reflections that can cause network faults.

Length

Length results show the length of each cable pair. The
PASS/FAIL result is assigned based on the shortest measured
length. The lengths of the other pairs are shown with an
meaning the measurements are for informational purposes
only.
A 2 % to 5 % difference in measured length among cable
pairs is normal because of the following:
•
Signals travel at slightly different speeds in each cable
pair, but the tester uses the same speed to calculate the
length of each pair.
•
The twist rate varies slightly among cable pairs. If you
untwisted and straightened all the pairs, they would
have slightly different lengths.
Figure 3-12 shows a length results screen.
3-18
Differences between measured and actual length
values can be caused by variations in the cable's
NVP value. NVP values can vary among cable types,
lots, and manufacturers. In most cases, these
differences are minor and may be disregarded.
If the length of the shortest pair does not exceed
the limit by 10 %, then the length test passes even
if other pairs exceed the limit. This is the 10 % rule
for length, as given in the ANSI/TIA standard. See
the Fluke Networks Knowledge base for details.
i
,
Figure 3-12. Length Results
Notes
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