90 Keysight InfiniiVision 3000T X-Series Oscilloscopes User's Guide
4 FFT Spectral Analysis
• Max Hold — records the maximum vertical values found at each horizontal
bucket across multiple analysis cycles and uses those values to build a
waveform. This display mode is often referred to as Max Envelope.
• Min Hold — records the minimum vertical values found at each horizontal
bucket across multiple analysis cycles and uses those values to build a
waveform. This display mode is often referred to as Min Envelope.
• Span/Center or Start Freq/Stop Freq — this pair of softkeys let you define the
displayed frequency range. Press the softkeys to toggle between:
• Span/Center — Span specifies the frequency range represented by the
width of the display. Divide span by 10 to calculate the frequency scale
per division. Center specifies the frequency at the center vertical grid line
of the display.
• Start Freq/Stop Freq — Start Freq specifies the frequency at the left side of
the display. Stop Freq specifies the frequency at the right side of the
display.
To set desired values, tap the softkey label on screen for a keypad entry
dialog or turn the Entry knob.
• More FFT — displays the More FFT Settings Menu.
2 Press the More FFT softkey to display additional FFT settings.
• Window— selects a window to apply to your FFT input signal:
• Hanning — window for making accurate frequency measurements or for
resolving two frequencies that are close together.
• Flat Top — window for making accurate amplitude measurements of
frequency peaks.
• Rectangular — good frequency resolution and amplitude accuracy, but use
only where there will be no leakage effects. Use on self-windowing
waveforms such as pseudo-random noise, impulses, sine bursts, and
decaying sinusoids.
• Blackman Harris — window reduces time resolution compared to a
rectangular window, but improves the capacity to detect smaller impulses
due to lower secondary lobes.
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