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be determined. However, repeated samples
were taken from the trial to validate qualitative
findings noted below. Distinct differences can
be seen in some of the set points mainly in
the form of spikes in the NEXT graphs. At one
combination of pretwist ratio and bow speed
an obvious spike appears in the NEXT graph at
80 MHz. By changing only the pretwist ratio for
both pairs, this spike is reduced or eliminated.
At the opposite setting of bow speed, the
change in pretwist ratio has a similar effect on a
spike that is seen at about 125 MHz.
3 Conclusion
As a result of this study there were a number of
important findings. It has been shown that the
high speed measurement technology used in
this study provides an accurate and repeatable
method for measurement of lay length value
of twisted pairs. The use of this technique
over long lengths along with real time data
collection of the speed of the pair provides
insight, through FFT analysis, into the stability
of, and patterns within, the twinning process.
Mainly, lay variation signatures are found at the
fundamental pair lay length, the twinner bow
speed and the pretwist speed.
The nominal lay length values are affected by
changes in process set points, specifically
pretwist ratio and its interaction with bow
speed. Quantitatively, these changes are
relatively small. But there appears to be a
relationship between the inputs and the lay
lengths that would require further validation
for statistical significance. An additional and
potentially larger impact to the nominal lay
length can be seen between machine types.
Subsequent processes can add to or have an
impact on the variation signatures. This was
evident in the measurement of pairs at cabling.
Additional signatures for cabler bow speed and
take up spool diameter were seen.
Finally, and most importantly, crosstalk
performance is significantly affected by
the process changes in these experiments.
Investigation into the changes in lay length
values as well as changes in the variation
signatures are needed to verify the contribution
from each factor. It is reasonable to assume
that there are other process inputs that could
have an impact to the lay variation as there
are other unexplained signatures seen at both
twinning and cabling. Their impact to crosstalk
performance would require further investigation.
❍
❍ Figure 11: Spike at 80 MHz in one trial
❍
❍ Figure 12: Spike missing at 80 MHz after pretwist changes
❍
❍ Figure 13: Spike reduced at 125 MHz after pretwist changes
Kenneth E Cornelison
Beta LaserMike
Dayton, Ohio
USA
Email:
Website:
Stephen Pearson
Tyco Electronics
Greensboro , North Carolina
USA
Email:
Website: