Math setups Set up spectral gating controls
Resolution bandwidth
The resolution bandwidth controls the bandwidth of the spectral analyzer filters. You can adjust the
resolution bandwidth in units of hertz. The resolution bandwidth is measured at the –3 dB points on
each side of the pea k spectral lobe of the filter.
Resolution bandwidth is inversely proportional to the gate duration in the time domain. Changing the
gate duration changes the resolution bandwidth. Changing the spectral analyzer window function also
changes the
resolution bandwidth but will not affect the gate duration.
To decrease the resolution bandwidth beyond the present limits, increase the time domain gate
duration.
If this is insufficient, increase the record length and then increase the gate duration
again. You can also try the rectangular or Hamming window to maximize the frequency resolution
(minimize resolution bandwidth).
Set up spectral gating controls
From the Math menu, select Adva nced Spectral, or click Advanced in the Math Setup control window.
To use
1. Select an FFT window type from the Window Type list.
2. Click in the Gate Position, Gate Duration, or Ga te Length entry boxes and use the multipurpose
knobs to set the gating parameters.
Behavior
An FFT Window Type (see page 906) can help reduce spectral noise for m any types of signals. Some
windows provide better frequency resolution at the expense of better amplitude measurements. Other
DSA/DPO70000D, MSO/DPO/DSA70000C, DPO7000C, and MSO/DPO5000 Series 249
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