Fluke CableIQ, User Manual, Page: 54 / 92

CableIQ Qualification Tester
Users Manual
44
TDR Plot for Coaxial Cabling
Discover mode includes a TDR (time domain
reflectometry) plot. TDR is like radar. The tester sends a
pulse down the cable, and receives reflections from
impedance changes along the cable. The tester then
plots the reflections on a distance scale to show you
where impedance changes occur. Signal reflections are
undesirable because they can cause poor CATV reception.
The Appendix lists some causes of impedance changes.
Figure 17 shows examples of TDR plots with some of
these faults.
avv36f.eps
A
The vertical scale represents change in impedance (
∆
Z ).
B
The distance to the cursor (
D
).
C
Use
B C
to move the cursor. Use
AD
to zoom horizontally at the
cursor’s location.
D
Cursor. Use
B C
to move the cursor.
E
Reflection from an open, or from the wiremap adapter. Opens and
other increases in impedance cause positive spikes on the trace.
-continued-
Figure 17. TDR Plots for Coaxial Cabling