User Manual

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฀
฀
฀
฀
฀
฀