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Spectral Controls: Gating
Access this control window from the Math menu Spectral Controls command or the Controls button on
the Spectral Setup control window.
Overview
Use the gating controls to specify a segment of the time domain record to analyze in the frequency
domain.
To Use
Select the FFT window type from the drop-down list. Use the
multipurpose knobs to set the gating parameters.
Behavior
Gate Pos (Gate Position) moves the gate that selects the data for
the spectral waveform. The gate position is the center point in the
gate measured in seconds with respect to the trigger point. In most
cases the phase reference point is located at the center of the gated
data. However, if you use a Tek Exponential window, the phase
reference point is at the 20% point of the gated data.
Gate Dur (Gate Duration) sets the gate time duration in seconds.
The default gate duration is the duration of the entire waveform
record. The resolution bandwidth is inversely proportional to the
gate duration.
An FFT Window Type can help reduce spectral noise for many
types of signals. Some windows provide better frequency
resolution at the expense of better amplitude measurements.
Other windows provide better amplitude accuracy over frequency resolution. The choice of
window also affects the resolution bandwidth. Res BW (Resolution Bandwidth) determines how
small of a frequency difference can be resolved in the frequency domain output data. It defines the
bandwidth of filters used to perform the frequency domain analysis. The resolution bandwidth is
measured in hertz at the 3 dB points on each side of the peak spectral lobe.
Adjusting the resolution bandwidth controls the gate duration to obtain the desired resolution
bandwidth.
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