AEA Technology 20TDR, Basic Manual

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Figure 2-18 is an example of a bridged tap on a twisted pair cable. The tap starts at the
downward excursion and ends at the point the trace starts upward. Taps can be spliced on the
pair or be a drop cord plugged into a wall outlet. Bridge Taps are common on older homes and
business wired using the telco loop. Bridge Taps should never appear on a network wired to TIA’s
568B or TIA’s 570 building wiring standards which use “home run” or “star” wiring configurations.
Figure 2-18
Figure 2-19 is an example of a twisted pair cable with a split pair (one wire from one pair crossed
with one wire from another pair running in the same cable jacket), and a re-split which corrected
the split at the next junction. Split is marked by Cursor 2 at 94 ft and the re-split by Cursor 1. The
CRSR
∆
indicates the distance and impedance change between Cursor 2 and Cursor 1.
Figure 2-19
Figure 2-20 is an example of a wet twisted pair cable. Remember TDR distances in and after the
wet section are shorter than actual length and invalid as the velocity reduces to an unknown.
However, a wet section of cable will always have an erratic lower impedance spot in the trace.
Figure 2-20
For more example traces and more detailed explanations of the impedance and velocity affects,
particularly for avionics TDR uses testing single-wires in a harness, refer to the Operation Manual
on the TDR’s CD or download the Operation Manual from our web site at
www.aeatechnology.com .