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990DSL
Users Guide
Reflections
Reflections are caused by discontinuities in a cable's characteristic impedance,
such as gauge changes, splices, faults, the cable's end, or series network
elements. Positive (in-phase) reflections result from sudden increases in cable
impedance, such as those due to opens, load coils, or resistive splices.
Negative (out-of-phase) reflections result from decreases in cable impedance,
such as those due to resistive faults (for example, shorts, grounds, and crosses),
bridged taps, and build-out capacitors. A cable that has no faults or network
elements and is properly terminated in its characteristic impedance generates
no reflections.
TDR Auto-Test
The TDR Auto-Test is an automatic test. With the press of a single key, this
Auto-Test runs a sequence of parametric tests and a TDR test. Results from a
TDR Auto-Test can give you a quick— yet comprehensive— view of the
status of a pair. For the novice or infrequent operator of TDR equipment, the
TDR Auto-Test can provide a good starting point in the troubleshooting
process.
The TDR Auto-Test automatically flags and pinpoints the location of the
following types of faults:
•
Open conductors
•
Resistance shorts
•
Load coils
•
Bridged taps
•
Bad splice joints
•
Pair Splits
6-4
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