tional method is the discontinuity is relatively small
and, therefore, the TDR’s reflection will be small. If the
split is close, it can be identified. If, on the other hand,
the split is some distance away, the small reflection is
attenuated by cable length and the split can be difficult
to locate.
Using the Model 3300 in the Crosstalk mode greatly
enhances the reflection and makes finding splits that are
far away much easier.
Shown below is an example of a split, and split/resplit
and their corresponding TDR waveforms using the
crosstalk mode.
Connect one pair of the split pair to Line 1 and the other
pair to Line 2. Set the Model 3300 to display Line 1 and
adjust the 1st cursor to the “0” distance marker. Cycle
the Model 3300 display mode to the Crosstalk mode.
The Crosstalk mode transmits the TDR pulse on Line 1
and receives on Line 2. If any energy is coupled from
pair 1 to pair 2 (split or resplit), it will return to the
instrument and be displayed on the waveform trace. Use
the Range horizontal zoom, waveform position, and
vertical gain functions to find the discontinuity. Set the
cursor to this point. Now you have found the locations
of the split and resplit.
4.2 Locating Bridged Taps
A bridged tap is a component within a telephone system
that can be one of the easiest to locate with a TDR, but
it is also often mis-identified.