Glossary
Aberrations Imperfections or undesired variations in a signal. For example, aberrations in a
TDR’s excitation signal are the result of the finite switching speed of the instrument’s
electronics and cause it to deviate from a perfect step signal.
AC Alternating current, a method of delivering electrical energy by periodically changing the
direction of the electric field in a conductor.
Accuracy The difference between a measured or estimated value of a quantity and its true value.
Accuracy and precision are both important factors to consider when assessing the reliability
of a measurement.
Analog Refers to a signal that is continuous with respect to both time and value. Analog circuitry
produces and/or measures analog signals. This is in contradistinction to digital signals, which
are discontinuous in both time and value. The sampling circuitry of a TDR converts the
analog voltage signal detected on a cable to a digital value for representation on the display
and in the instrument’s memory.
Cable Conductors of electricity that are usually shielded and insulated. Cables typically contain at
least two conductors, one to deliver the electrical signal and one to act as the return path.
The conductor acting as the return path may be referred to as the “shield”, “ground”, or
“ground wire”. A cable with such a ground return path is known as an unbalanced cable, an
example of which is typical coaxial cable. Another general type of cable is called balanced
cable, an example of which is twisted-pair Ethernet cable. In balanced cable, two signal wires
carrying differential signals of opposite polarity are both separated from ground by an equal
impedance.
Cable Attenuation A quantity describing the energy in a signal that is absorbed, reflected, or
otherwise lost during propagation through a cable. Higher frequencies are typically the most
susceptible to attenuation. Cable attenuation can distort some TDR measurements.
Attenuation is often expressed in decibels (dB) at one or more frequencies. See also dB
and Return Loss.
Cable Fault A defect in a cable or other condition that makes a cable less able to deliver electrical
energy than was designed. Damage to the shield, conductor, or insulation, bad splices, and
poorly mated connectors are frequently encountered cable faults.
Capacitance See Reactance
Characteristic Impedance The ratio of the amplitude of voltage and current in an electrical signal
propagating in a cable. In a coaxial cable, this value (usually written Z
0
) is, in large part,
related to the geometrical relationship of conductor to return path conductor. Cables are
usually designed to match the impedance of the source and load to which they are attached
in order to maximize power transfer.
Conductor A substance that allows electricity to flow through it with minimal resistance. Most
conductors are metals. However, there are many non-metallic conductors, including salt
solutions, graphite, and any element in its plasma state.
CT100B TDR Cable Analyzers Operator’s Manual 141
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