SPECTRUM ANALYZERS BASIC
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.
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
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.
Full span: For most modern spectrum analyzers, full span means a frequency span that covers the entire tuning range of the analyzer. These analyzers include single band RF analyzers and microwave analyzers such as the ESA and PSA Series that
Input attenuator: A step attenuator between the input connector and first mixer of a spectrum analyzer. Also called the RF attenuator. The input attenuator is used to adjust level of the signal incident upon the first mixer. The attenuator is used to prevent gain compression due to high-level and/or broadband signals and to set dynamic range by controlling the degree of internally generated distortion. In some analyzers, the vertical position of displayed signals is changed when the input attenuator setting is changed,
so the reference level is also changed accordingly. In modern Agilent analyzers, the IF gain is changed to compensate for input attenuator changes, so signals remain stationary on the display, and the reference level is not changed.
Input impedance: The terminating impedance that the analyzer presents to the signal source. The nominal impedance for RF and microwave analyzers is usually 50 ohms. For some systems, e.g. cable TV, 75 ohms is standard. The degree of mismatch between the nominal and actual input impedance is given in terms of VSWR (voltage standing wave ratio).
so the reference level is also changed accordingly. In modern Agilent analyzers, the IF gain is changed to compensate for input attenuator changes, so signals remain stationary on the display, and the reference level is not changed.
Input impedance: The terminating impedance that the analyzer presents to the signal source. The nominal impedance for RF and microwave analyzers is usually 50 ohms. For some systems, e.g. cable TV, 75 ohms is standard. The degree of mismatch between the nominal and actual input impedance is given in terms of VSWR (voltage standing wave ratio).
Marker: A visible indicator that we can place anywhere along the displayed signal trace. A read out indicates the absolute value of both the frequency and amplitude of the trace at the marked point. The amplitude value is given in the currently selected units. Also see Delta marker and Noise marker.
Measurement range: The ratio, expressed in dB, of the maximum signal level that can be measured (usually the maximum safe input level) to the lowest achievable average noise level. This ratio is almost always much greater than can be realized in a single measurement. See Dynamic range.
Measurement range: The ratio, expressed in dB, of the maximum signal level that can be measured (usually the maximum safe input level) to the lowest achievable average noise level. This ratio is almost always much greater than can be realized in a single measurement. See Dynamic range.
Resolution: See Frequency resolution.
Resolution bandwidth: The width of the resolution bandwidth (IF) filter of a spectrum analyzer at some level below the minimum insertion loss point (maximum deflection point on the display). For Agilent analyzers, the 3 dB bandwidth is specified; for some others, it is the 6 dB bandwidth.
Resolution bandwidth: The width of the resolution bandwidth (IF) filter of a spectrum analyzer at some level below the minimum insertion loss point (maximum deflection point on the display). For Agilent analyzers, the 3 dB bandwidth is specified; for some others, it is the 6 dB bandwidth.
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 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.
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.
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.
Video: In a spectrum analyzer, a term describing the output of the envelope detector. The frequency range extends from 0 Hz to a frequency typically well beyond the widest resolution bandwidth available in the analyzer. However, the ultimate bandwidth of the video chain is determined by the setting of the video filter.
Video bandwidth: The cutoff frequency (3 dB point) of an adjustable low pass filter in the video circuit. When the video bandwidth is equal to or less than the resolution bandwidth, the video circuit cannot fully respond to the more rapid fluctuations of the output of the envelope detector. The result is a smoothing of the trace, i. e. a reduction in the peak-to-peak excursion of broadband signals such as noise and pulsed RF when viewed in the broadband mode. The degree of averaging or smoothing is a function
of the ratio of the video bandwidth to the resolution bandwidth.
Video filter: A post-detection, low-pass filter that determines the bandwidth of the video amplifier. Used to average or smooth a trace. See Video bandwidth.
Zero span: That case in which a spectrum analyzer's LO remains fixed at a given frequency so the analyzer becomes a fixed-tuned receiver. The bandwidth of the receiver is that of the resolution (IF) bandwidth. Signal amplitude variations are displayed as a function of time. To avoid any loss of signal information, the resolution bandwidth must be as wide as the signal bandwidth. To avoid any smoothing, the video bandwidth must be set wider than the resolution bandwidth.
of the ratio of the video bandwidth to the resolution bandwidth.
Video filter: A post-detection, low-pass filter that determines the bandwidth of the video amplifier. Used to average or smooth a trace. See Video bandwidth.
Zero span: That case in which a spectrum analyzer's LO remains fixed at a given frequency so the analyzer becomes a fixed-tuned receiver. The bandwidth of the receiver is that of the resolution (IF) bandwidth. Signal amplitude variations are displayed as a function of time. To avoid any loss of signal information, the resolution bandwidth must be as wide as the signal bandwidth. To avoid any smoothing, the video bandwidth must be set wider than the resolution bandwidth.
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