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1205CXB OPERATION MANUAL v1
Introduction
Description and Overview
The 1205CXB™ is a High Resolution Cable Fault Locator, also known as a Cable Radar or a Time Domain
Reflectometer (TDR). The 1205CXB transmits electrical pulses into a cable, and a portion of the pulse
energy reflects back from cable imperfections. These can be discontinuities (eg cable joints, changes in
cable type or the far end of the cable under test) or faults (typically short circuits, open circuits, water
ingress or corroded connections).
The transmitted pulse and the reflected pulse(s) are shown on the display. The time taken by the pulse
to travel to the imperfection and back is a measure of the distance to the fault. Position the cursor at
the start of the reflected pulse to ensure that the distance to the discontinuity is shown accurately. You
may assess the type of imperfection by analyzing the displayed waveform.
Reflections from an impedance higher than the characteristic impedance of the cable, and from
inductive faults, are upwards. Reflections from an impedance lower than the characteristic impedance
of the cable, as well as capacitive faults, are downwards.
NOTE: The 1205CXB has been specially designed to analyze coaxial cables but can be used on any cable
that contains at least two conductors or one conductor and a metallic screen.
Velocity of Propagation (VOP)
The properties of the cable, mainly the insulation between the two conductors, greatly affect the
velocity of the pulses traveling along the cable. This velocity is known as the Velocity of Propagation
(VOP), or Velocity Factor (PVF), while some cable datasheets refer to the Dielectric Constant. The
1205CXB uses this value to calculate distance, so it is important for this to be as accurate as possible.
The 1205CXB can accept user selectable values for the VOP of between 10.0 and 99.9%.
Typical VOPs for some common cable types
The VOP and characteristic impedance values for some common cable types are:
Use/Type
Cable type
CATV and Coax
Air
Air Spaced Coaxial
Dynafoam
Foam Poly
PARA I
QR PARA III
RG6, RG11, RG59
Solid PE
T, TR
TX, TX10
Times Fiber RG59
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VoP
0.98
0.94
0.9
0.82
0.82
0.88
0.82
0.67
0.87
0.89
0.93
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