70 Agilent InfiniiVision 2000 X-Series Oscilloscopes User's Guide
4 Math Waveforms
• 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.
• Vertical Units — lets you select Decibels or V RMS as the units for the
FFT vertical scale.
• 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 above the softkeys.
Scale and offset considerations
If you do not manually change the FFT scale or offset settings, when you turn the horizontal
scale knob, the span and center frequency settings will automatically change to allow
optimum viewing of the full spectrum.
If you do manually set scale or offset, turning the horizontal scale knob will not change the
span or center frequency settings, allowing you see better detail around a specific
frequency.
Pressing the FFT Auto Setup softkey will automatically rescale the waveform and span and
center will again automatically track the horizontal scale setting.
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