Specifications

Chapter 15 137
Concepts
Time Gating Concepts
Concepts
With video gating the analyzer is continually sweeping, independent of
the position and length of the gate. The analyzer must be swept at a
minimum sweep time (see the sweep time calculations later in this
chapter) to capture the signal when the gate is passing a signal.
Because of this, video gating is typically slower than gated LO and
gated FFT.
Figure 15-8 Gated Video ESA Spectrum Analyzer Block Diagram
NOTE Gated video is available only on the Agilent ESA-E Series spectrum
analyzers (E4401B, E4402B, E4404B, E4405B and E4407B) with option
1D6.
Gated FFT Concepts (PSA Spectrum Analyzer)
Gated FFT (Fast-Fourier Transform) is an FFT measurement which
begins when the trigger conditions are satisfied.
The process of making a spectrum measurement with FFTs is
inherently a “gated” process, in that the spectrum is computed from a
time record of short duration, much like a gate signal in swept-gated
analysis.
Using the PSA in FFT mode, the duration of the time record to be gated
is:
The duration of the time record is within a tolerance of approximately
3% for resolution bandwidths up through 1 MHz. Unlike swept gated
analysis, the duration of the analysis in gated FFT is fixed by the RBW,
not by the gate signal. Because FFT analysis is faster than swept
analysis (up to 10 MHz), the gated FFT measurements can have better
frequency resolution (a narrower RBW) than swept analysis for a given
duration of the signal to be analyzed.
FFT Time Record (to be gated)
1.83
RBW
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