Keysight InfiniiVision HD3 Series - Page 67

FFT Spectral Analysis 4
Keysight InfiniiVision HD3-Series Oscilloscopes User's Guide 67
You can also make this adjustment using the touchscreen in waveform drag
mode.
The offset value is the value at the vertical center of the display.
• Analysis Precision... — Opens the Analysis Precision dialog box where you can
enable the precision analysis record (for measurements and math function
waveforms) and specify its length. See "The Analysis Record and Waveform
Math"
on page 95.
• Input — Selects how the displayed frequency range is entered:
• Center/Span — 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/Stop — Start Freq specifies the frequency at the left side of the display.
Stop Freq specifies the frequency at the right side of the display.
• Source 1 — Select the analog channel, math function, or reference waveform on
which to perform the FFT.
• Readout — Specifies how the FFT resolution is displayed: Off, Sample Rate, Bin
Size, RBW (Resolution Bandwidth).
• Display Mode — selects one of these FFT waveform display modes:
• Normal — this is the FFT waveform without any averaging or hold functions
applied. This is how FFT math function waveforms are displayed.
• Averaged Value — the FFT waveform is averaged the selected number of
times. Averages are calculated using a "decaying average" approximation,
where:
next_average = current_average + (new_data - current_average)/N
Where N starts at 1 for the first acquisition and increments for each
following acquisition until it reaches the selected number of averages, where
it holds.
• 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.
• Auto Setup — Sets the frequency Span and Center to values that will cause the
entire available spectrum to be displayed. The maximum available frequency is
half the FFT sample rate, which is a function of the time per division setting.
The FFT resolution is the quotient of the sampling rate and the number of FFT
points (f
S
/N). The current FFT Resolution is displayed on screen.
• Add Max Function — Adds another math function waveform that is the Max Hold
operator on the FFT math function waveform.