EXFO CableSHARK P3 VF/DSL Cable Qualifier - Manual (Page 151)

CableSHARK P3 User Guide
139
8.8.. 4-Wire Crosstalk Test
The CableSHARK’s 4 Wire Crosstalk test or 4 WIRE XTALK Test or Stressed Noise test allows users to
measure and observe crosstalk on cable pairs that are currently in use or being provisioned for xDSL. One
major impairment for which the 4wire crosstalk measurement is well suited for is for detecting and
determining the severity of split pairs.
Service Providers have often had to resort to using split pairs to add a subscriber. Using the good
conductors from two defective pairs, a split pair is created. While this works well for plain old telephone
service (POTS), it is disastrous for the broadband signals of DSL. Telephone cables are twisted to minimize
the amount of induced differential noise caused by crosstalk from adjacent pairs. When a split pair is used,
the two conductors are no longer twisted together to form the correct cancellation effect. This causes
crosstalk to occur.
8.8.1 Setting up a 4-Wire Crosstalk Test
From the Main Menu, pressing function button F1 (CABLE TESTS) will bring the user to the CABLE TESTS
pop-up menu. The following sections will explain the operation of this test. Figure 8.8.1A below shows the 4
Wire Crosstalk Test Setup Menu.