Making Measurements 5
6000 Series Oscilloscope User’s Guide 227
•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.
3To make cursors measurements, press the Cursors key and set
the Source softkey to Math.
Use the X1 and X2 cursors to measure frequency values and
difference between two frequency values (∆X). Use the Y1
and Y2 cursors to measure amplitude in dB and difference in
amplitude (∆Y).
4To make other measurements, press the Quick Meas key and
set the Source softkey to Math.
You can make peak-to-peak, maximum, minimum, and
average dB measurements on the FFT waveform. You can
also find the frequency value at the first occurrence of the
waveform maximum by using the X at Max measurement.
The following FFT spectrum was obtained by connecting the
front panel Probe Comp signal (~1.2kHz) to channel 1. Set
sweep speed to 5 ms/div, vertical sensitivity to 500 mV/div,
Units/div to 10 dBV, Offset to -34.0 dBV, Center frequency to
5.00 kHz, frequency Span to 10.0 kHz, and window to Hanning.
Scale and offset considerations
If you do not manually change the FFT scale or offset settings, when you turn the
horizontal sweep speed 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 sweep speed knob will not change the
span or center frequency settings, allowing you see better detail around a specific
frequency. Pressing the FFT Preset softkey will automatically rescale the
waveform and span and center will again automatically track the horizontal
sweep speed setting.