Power Sum NEXT (PSNEXT)
Power Sum NEXT (PSNEXT) is a calculation, not a measurement.
PSNEXT is derived from the summation of the individual NEXT
effects on each pair by the other three pairs. PSNEXT is important
measurements for qualifying cabling intended to support 4 pair
transmission schemes such as Gigabit Ethernet, although IEE
8023.ab does not specifically require PSNEXT. If you run the
specific Gigabit Ethernet test within the field tester, you
will see that PSNEXT is not recorded. There are four PSNEXT
results at each end of the link per link tested.
Results Interpretation
 Since
PSNEXT is a measure of difference in signal strength between
disturbing pairs and a disturbed pair, a larger number (less
crosstalk) is more desirable than a smaller number (more crosstalk).
Because PSNEXT varies significantly with frequency, it is
important to measure it across a range of frequencies, typically
1 ?100 MHz. If you look at the PSNEXT on a 50 meter segment
of twisted pair cabling, it has a characteristic "roller
coaster" shape. That is, it varies up and down significantly,
while generally increasing in magnitude. This is because twisted
pair coupling becomes less effective for higher frequencies.
Typically, PSNEXT results are around 3 dB lower than the worst-case
NEXT result at each end of the link.
Troubleshooting Recommendations
Since PSNEXT is a calculation based on NEXT measurements,
troubleshooting for PSNEXT failures reduces to troubleshooting
for NEXT problems. Once you have isolated and repaired the
NEXT problem, PSNEXT will automatically improve. Troubleshooting
NEXT requires a field tester with the ability to look down
the cable and see where the crosstalk is happening.
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