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CHAPTER 8: Testing Twisted-Pair Cable
NEXT is measured in decibels (dB). A high dB value, which is typically
referred to as low NEXT, is good (for example, 48 dB). This means there is
a large difference between the transmitted signal and the resulting NEXT.
A low dB value, which is typically referred to as high NEXT, is bad (for
example, 20 dB). This means NEXT is significant in relation to the
transmitted signal.
The table on the next page describes some common causes of NEXT
and their solutions.
Common Causes of
Solution
Excessive NEXT
Bad or low-grade
Patch cables may not be twisted pair. A common mistake is
patch cables
to use silver-satin untwisted cable for data applications.
Patch cable could be wired incorrectly. Check twisted pairs
per the EIA/TIA 568 pairing.
Check patch cable and rewire or replace as necessary.
Terminating points
NEXT problems are most common at the
termination points. Untwisting of the wires too far from the
termination is very common. Follow the procedure for
“
NEXT test fails one or more pairs
” to troubleshoot.
Split pairs
Because of different standards, there are different pair
combinations (for example, USOC, EIA/TIA, etc.). Double-
check requirements and rewire if necessary. For
troubleshooting, follow procedure for “
Split Pair
” in
Section 8.2.1
.
Use of substandard
It is common to make the mistake of using couplers or lower-
components
grade hardware or cable than the minimum expected.
(termination
The highest category your installation will comply to is that
components, cable)
of the lowest-category component you have in your segment.
Summary of Contents for SCAN-LAN VI
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