Agilent Spectrum Analysis Basics - Agilent Technologies

Glossary of Terms
Absolute amplitude accuracy: The uncertainty of an amplitude
measurement in absolute terms, either volts or power. Includes relative
uncertainties (see Relative amplitude accuracy) plus calibrator uncertainty.
For improved accuracy, some spectrum analyzers have frequency response
specified relative to the calibrator as well as relative to the mid-point
between peak-to-peak extremes.
ACPR: Adjacent channel power ratio is a measure of how much signal
energy from one communication channel spills over, or leaks into an adjacent
channel. This is an important metric in digital communication components
and systems, as too much leakage will cause interference on adjacent
channels. It is sometimes also described as ACLR, or adjacent channel
leakage ratio.
Amplitude accuracy: The uncertainty of an amplitude measurement. It can
be expressed either as an absolute term or relative to another reference point.
Amplitude reference signal: A signal of precise frequency and amplitude
that the analyzer uses for self-calibration.
Analog display: The technique in which analog signal information (from the
envelope detector) is written directly to the display, typically implemented
on a cathode ray tube (CRT). Analog displays were once the standard method
of displaying information on a spectrum analyzer. However, modern spectrum
analyzers no longer use this technique, but instead, use digital displays.
Average detection: A method of detection that sums power across a
frequency interval. It is often used for measuring complex, digitally
modulated signals and other types of signals with noise-like characteristics.
Modern Agilent spectrum analyzers typically offer three types of average
detection: power (rms) averaging, which measures the true average power
over a bucket interval; voltage averaging, which measures the average
voltage data over a bucket interval; and log-power (video) averaging, which
measures the logarithmic amplitude in dB of the envelope of the signal
during the bucket interval.
Average noise level: See Displayed average noise level.
Bandwidth selectivity: A measure of an analyzer’s ability to resolve
signals unequal in amplitude. Also called shape factor, bandwidth selectivity
is the ratio of the 60 dB bandwidth to the 3 dB bandwidth for a given
resolution (IF) filter. For some analyzers, the 6 dB bandwidth is used in
lieu of the 3 dB bandwidth. In either case, bandwidth selectivity tells us
how steep the filter skirts are.
Blocking capacitor: A filter that keeps unwanted low frequency signals
(including DC) from damaging circuitry. A blocking capacitor limits the
lowest frequency that can be measured accurately.
CDMA: Code division multiple access is a method of digital communication
in which multiple communication streams are orthogonally coded, enabling
them to share a common frequency channel. It is a popular technique
used in a number of widely used mobile communication systems.
Constellation diagram: A display type commonly used when analyzing
digitally modulated signals in which the detected symbol points are plotted
on an IQ graph.
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