User`s guide

Math Waveforms 4
Agilent InfiniiVision 2000 X-Series Oscilloscopes User's Guide 69
• 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.
3 To make cursor measurements, press the [Cursors] key and set the
Source softkey to Math: f(t).
Use the X1 and X2 cursors to measure frequency values and difference
between two frequency values (ΔX). Use the Y1 and Y2 cursors to
measure amplitude in dB and difference in amplitude (ΔY).
4 To make other measurements, press the [Meas] key and set the Source
softkey to Math: f(t).
NOTE
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.