Specifications

118
Spectrum: An array of sine waves of differing frequencies and amplitudes
and properly related with respect to phase that, taken as a whole, constitute
a particular time-domain signal.
Spectrum analyzer: A device that effectively performs a Fourier transform
and displays the individual spectral components (sine waves) that constitute
a time-domain signal. Phase may or may not be preserved, depending upon
the analyzer type and design.
Spurious responses: The improper responses that appear on a spectrum
analyzer display as a result of the input signal. Internally generated
distortion products are spurious responses, as are image and multiple
responses.
Sweep time: The time to tune the LO across the selected span. Sweep
time does not include the dead time between the completion of one sweep
and the start of the next. In zero span, the spectrum analyzer’s LO is fixed,
so the horizontal axis of the display is calibrated in time only. In non-zero
spans, the horizontal axis is calibrated in both frequency and time, and
sweep time is usually a function of frequency span, resolution bandwidth,
and video bandwidth.
Time gating: A method of controlling the frequency sweep of the spectrum
analyzer based on the characteristics of the signal being measured. It is
often useful when analyzing pulsed or burst modulated signals; time
multiplexed signals, as well as intermittent signals.
TDMA: Time division multiple access is a digital communication method
in which multiple communication streams are interleaved in time, enabling
them to share a common frequency channel.
Units: Dimensions of the measured quantities. Units usually refer to
amplitude quantities because they can be changed. In modern spectrum
analyzers, available units are dBm (dB relative to 1 milliwatt dissipated
in the nominal input impedance of the analyzer), dBmV (dB relative to
1 millivolt), dBuV (dB relative to 1 microvolt), volts, and in some analyzers,
watts. In Agilent analyzers, we can specify any units in both log and
linear displays.
Vector diagram: A display type commonly used when analyzing digitally
modulated signals. It is similar to a constellation display, except that in
addition to the detected symbol points, the instantaneous power levels
during state transitions are also plotted on an IQ graph.
Vector display: A display type used in earlier spectrum analyzer designs,
in which the electron beam was directed so that the image (trace, graticule,
annotation) was written directly on the CRT face, not created from a series
of dots as in the raster displays commonly used today.