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