5 Measurements and Math Functions
200 InfiniiVision 7000B Series Oscilloscopes User’s Guide
• 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.
• Span — sets the overall width of the FFT spectrum that you see on
the display (left to right). Divide span by 10 to calculate the number
of Hertz per division. It is possible to set Span above the maximum
available frequency, in which case the displayed spectrum will not
take up the whole screen. Press the Span softkey, then turn the Entry
knob to set the desired frequency span of the display.
• Center — sets the FFT spectrum frequency represented at the center
vertical grid line of the display. It is possible to set the Center to
values below half the span or above the maximum available
frequency, in which case the displayed spectrum will not take up the
whole screen. Press the Center softkey, then turn the Entry knob to
set the desired center frequency of the display.
• Scale — lets you set your own vertical scale factors for FFT expressed
in dB/div (decibels/division). Press the Scale softkey, then turn the
Entry knob to rescale your math function.
• Offset — lets you set your own offset for the FFT. The offset value is
in dB and is represented by the center horizontal grid line of the
display. Press the Offset softkey, then turn the Entry knob to change
the offset of your math function.
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