Glossary
considered a complete characterization of a linear device for the frequency range of the
scattering parameters.
Short Circuit The condition in which the conductor in a cable or circuit comes into direct contact
with the return path conductor or earth ground. The electrical length of the cable measured
by TDR is shortened to the point of the short circuit.
Smith Chart A method for displaying complex valued electrical measurements, such as an S
11
, on
a polar plot, graphically showing both magnitude and phase angle.
Smoothing Any technique for reducing noise in a signal. The CT100B uses time averaging to
smooth traces.
SP232 A serial protocol used by the Tektronix 1502B and 1502C. This protocol allowed
transmission of TDR trace data across a serial port. Using a USB to serial port adapter, a
CT100B can emulate this protocol.
Stability The change in the accuracy of a measurement or piece of test equipment over a period of
time such as the calibration interval. Stability may also refer to changes in accuracy related
to a specific environmental influence such as vibration, temperature, or humidity.
TDR Acronym for Time-Domain Reflectometer or Reflectometry. TDR instruments use a form of
closed-circuit radar to detect cable faults. A series of pulses are sent into a cable and
reflected voltage is measured as a function of time. If the velocity of propagation (Vp) is
known, the length of a cable and the distance to cable faults can be determined. TDR traces
produced by step-rise TDRs like the CT100B describe the impedance of a cable along its
length and can accurately detect a wide range of cable faults that can impair high-frequency
analog/RF and digital communications systems.
Trace A displayed or stored signal. When displayed, a trace appears as a line across the screen. A
trace may be a direct TDR measurement, as with the live trace, or derived trace, such as a
difference trace or an S
11
trace. A trace is sometimes referred to as a “waveform”. A scanned
or saved trace may be called a “scan”. A trace is a visual representation of the waveform
generated by a TDR. Traces on the CT100B may be in either time or frequency domain
depending upon their purpose.
Trace Averaging See Noise.
USB Universal Serial Bus. A common system for connecting a peripheral, such as a printer,
phone, or CT100B, to a computer.
Velocity of Propagation (Vp) Velocity of propagation of an electrical signal within a cable as a
fraction of c, the speed of light in a vacuum. Coaxial cable usually has a Vp of between 0.6
and 0.9.
Vertical Reference (Vert Ref) A feature of the CT100B that improves vertical measurements by
referencing them to scans from short and open calibration terminations.
CT100B TDR Cable Analyzers Operator’s Manual 145
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