176 Keysight N9927-90001 User’s Guide
SA (Spectrum Analyzer) Mode
SA Mode Settings
— Measure the spectrum of a signal in one time slot of a TDMA system.
— Exclude the spectrum of interfering signals, such as periodic pulse edge
transients that exist for only a limited time.
FFT Gating is a simple, efficient way to set the proper amount of trigger delay
and capture time so that signal artifacts of a repeating waveform or pulse can
be examined in the frequency domain. Learn more about trigger settings in
“Triggering” on page 172.
For best results, Auto Trigger should be used with this feature to ensure that
the sweep does not wait indefinitely for a trigger. Set Auto Trigger to a time
that is longer than the expected periodic rate of the signal. This is especially
important when using RF Burst or Video triggering in wider spans, because the
signal providing those triggers has limited bandwidth. Learn more about Auto
trigger in “Auto Trigger Time” on page 174.
For more conceptual information on this topic, please refer to Spectrum
Analysis Basics (App Note 150), pages 31 - 35, at
http://literature.cdn.keysight.com/litweb/pdf/5952-0292.pdf.
How to set FFT Gating
— Create a non-zero span measurement. Wider frequency spans take more
time to acquire.
—Press Sweep 3
—Then Trigger Settings
—Then FFT Gating Setup
— Then choose from the following:
—Gate View OFF ON
When ON, a separate zero span measurement is
displayed below the non-zero span window. The gate view
measurement helps to configure the gate width and delay by
revealing (with green markers) the location of the gate relative to the
trigger event. The zero span measurement is tuned to the center
frequency of the non-zero span measurement with about 5 MHz of
bandwidth. The Y-axis scale is the same for both windows.
—Gate View Time
Set the X-axis span for the non-zero span window.
Enter a value using the numeric keypad, the ?|? arrows, or the rotary
knob. This value is annotated as Swp (nn) below the window.
—FFT Gating OFF ON
When ON, the trigger type, gate width, and delay
are applied to the non-zero span measurement. The Res BW is set to
a value that is inversely proportional to the gate width.
—Gate Width
Set the width of the gating area within the non-zero span
window. The gating area is indicated by two vertical green lines. Enter
a value using the numeric keypad, the ?|? arrows, or the rotary knob.
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