Glossary
IP Internet Protocol. The universal protocol used to send data through the internet. Also used in
many other computer networks. Each computer on a network must have a unique IP address.
Jitter The uncertainty in measurement of time in a TDR. The main effect of jitter is to cause
apparent vertical noise in areas of changing impedance. Areas of constant impedance, such as
a flat segment of 50 Ω cable, will show no abnormality.
Layer Peeling A mathematical technique for reducing multiple reflections in a TDR trace. TDRs
measure reflections from changes in impedance, but if there are multiple impedance changes,
then the reflections from one will partially reflect back off of another. Reducing the effect of
these extra reflections improves the measurement of the impedance changes.
LCD Liquid crystal display. The display used by this instrument is an active-matrix thin-film
transistor LCD, abbreviated TFT-LCD.
Millirho (mρ) See Reflection Coefficient.
Noise Any undesirable electrical energy that impairs the ability of an electronic system to
transmit or receive a signal or make an accurate measurement. In TDR, noise is typically
related to thermal and/or electrical noise that interferes with the timebase or sampling
circuitry and is usually random, although a nearby strong electromagnetic radiator can cause
non-random synchronous noise to be measured on unshielded cable. In the case of random
noise, averaging is an effective means of noise suppression.
Open Circuit Describes a non-terminated cable or cable with a broken conductor that reflects all
energy within the incident pulse.
OSL (Open Short Load) A method of calibrating one-port analyzers using precision open, short,
and load terminations, where the load matches the output impedance of the analyzer. Each
termination contributes to reducing error in an S
11
measurement.
Phase A horizontal shift in a sinusoid. Phase is given as an angle. A sinusoid with phase of π
radians (180 degrees) is precisely inverted compared to the same sinusoid with 0 phase. A
sinusoid with phase of 2π radians (360 degrees) is precisely equal to the same sinusoid with
0 phase, i.e., it has no phase shift.
Precision The variation in the value of a variable measured multiple times. Precision and accuracy
are both important factors in determining the reliability of a given measurement. Precision
may also be used to describe the number of digits or the unit of the least significant digit
with which a particular quantity is expressed.
Reactance The imaginary component of electrical impedance. Reactance describes the opposition
of a conductor to the flow of alternating current. Impedance is described by Z = R + j · X
where R is resistance, j is the imaginary unit, and X is the reactance at a given frequency. If
X > 0, the impedance is inductive, if X = 0 then the impedance is purely resistive, and if
X < 0 the impedance is capacitive.
Reflection Coefficient In TDR, a coefficient describing the amplitude of a reflected signal
produced by an impedance mismatch in relation to the incident pulse. The reflection
coefficient Gamma (Γ) is defined by the relation Γ = (Z
t
− Z
0
)/(Z
t
+ Z
0
) where Z
t
is the
impedance at time t and Z
0
is the characteristic impedance of the cable, and is usually
described in parts per thousand with units of rho (ρ) or millirho (mρ). The coefficient ρ
ranges from -1 (short circuit) to +1 (open circuit). A reflection coefficient of zero indicates
that there is no impedance mismatch and no reflection of electrical energy.
CT100B TDR Cable Analyzers Operator’s Manual 143
To Next Page
Loading...