Multi LAN 350
Operation
45
In general TDR test helps to determine whether there are impedance anomalies on the
tested pair or cable. It is also possible to locate and determine the type of anomaly.
TDnext is used to crosstalk problems.
Some typical TDR and TDnext pictures together with comments are collected in the
following table.
Situation
Comment
TDR Display
Open cable,
cable break,
incorrect
termination etc.
(at short
distance)
Z
anom
>Z
cable
The pulse is reflected back at
the anomaly point. If the
instrument's output impedance
isn't matched to the cable's
then more than one reflection
can be seen.
Note: Cable length and cable
quality can be checked in this
way
Open cable,
cable break,
incorrect
termination
(at long
distance)
Z
anom
>Z
cable
The pulse is reflected back at
the anomaly point. Through
increasing attenuation
especially at high frequencies
the pulse's width is extended
and amplitude reduced.
Note: Cable length and cable
quality can be checked in this
way
Shorted cable,
incorrect
termination (at
middle distance)
Z
anom
<Z
cable
The pulse is completely
reflected back and inverted at
the anomaly point.
Note: Cable length and cable
quality can be checked in this
way
Problem at the
near connection
point
A part of the pulse is reflected
back at the very beginning.
The problem on the picture
was caused by a badly
assembled 1m patch cable.
Proper
termination, no
anomalies in
The pulse travels over the
cable without any reflections. If
the cable is correctly
