Fluke DSP-100 User Manual page 124

DSP-100/2000
Users Manual
Split Pairs and NEXT
A split pair occurs when one wire from a cable pair is twisted together with a wire
from a different cable pair. Split pairs most frequently result from miswires at
punchdown blocks and cable connectors. Figure 7-7 shows an example of split
pair wiring. Notice that the pin-to-pin connections across the cable are correct, but
the pairs twisted together do not form a complete circuit.
Split pairs cause severe crosstalk because the signals in the twisted pairs come
from different circuits. The high crosstalk levels produced by split pairs cause low
NEXT values during cable tests. If the NEXT value is low enough, the test tool
reports a split pair during the wire map test.
The tool may also report split pairs if you test untwisted cable, such as ribbon
cable or untwisted telephone line.
If the tool reports split pairs when you are testing a cable made of multiple
segments, you can determine which segment has the split pair by running the TDX
analyzer. The TDX analyzer plot will show a large value of crosstalk starting at a
distance that corresponds to the beginning of the segment with the split pair.
7-12
1
2
3
6
Incorrect Wiring: Split Pair
Figure 7-7. Split Pair Wiring
1
2
3
6
gc33f.eps