Agilent Spectrum Analysis Basics - Agilent Technologies

Dynamic range: The ratio, in dB, between the largest and smallest
signals simultaneously present at the spectrum analyzer input that can
be measured to a given degree of accuracy. Dynamic range generally refers
to measurement of distortion or intermodulation products.
Envelope detector: A circuit element whose output follows the envelope,
but not the instantaneous variation, of its input signal. In a superheterodyne
spectrum analyzer, the input to the envelope detector comes from the final
IF, and the output is a video signal. When we put our analyzer in zero span,
the envelope detector demodulates the input signal, and we can observe
the modulating signal as a function of time on the display.
Error vector magnitude (EVM): A quality metric in digital communication
systems. EVM is the magnitude of the vector difference at a given instant
in time between the ideal reference signal and the measured signal.
External mixer: An independent mixer, usually with a waveguide input
port, used to extend the frequency range of those spectrum analyzers
designed to utilize external mixers. The analyzer provides the LO signal
and, if needed, mixer bias. Mixing products are returned to the analyzer’s
IF input.
FFT (fast Fourier transform): A mathematical operation performed on
a time-domain signal to yield the individual spectral components that
constitute the signal. See Spectrum.
Flatness: See Frequency response.
Frequency accuracy: The uncertainty with which the frequency of a signal
or spectral component is indicated, either in an absolute sense or relative
to some other signal or spectral component. Absolute and relative frequency
accuracies are specified independently.
Frequency range: The minimum to maximum frequencies over which a
spectrum analyzer can tune. While the maximum frequency is generally
thought of in terms of an analyzer’s coaxial input, the range of many
microwave analyzers can be extended through use of external waveguide
mixers.
Frequency resolution: The ability of a spectrum analyzer to separate closely
spaced spectral components and display them individually. Resolution of
equal amplitude components is determined by resolution bandwidth. The
ability to resolve unequal amplitude signals is a function of both resolution
bandwidth and bandwidth selectivity.
Frequency response: Variation in the displayed amplitude of a signal as a
function of frequency (flatness). Typically specified in terms of ± dB relative
to the value midway between the extremes. Also may be specified relative
to the calibrator signal.
Frequency span: The frequency range represented by the horizontal axis
of the display. Generally, frequency span is given as the total span across
the full display. Some earlier analyzers indicate frequency span (scan width)
on a per-division basis.
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