Important Concepts: Time Gating (Time Gating)

This topic contains important concepts when using time gating.

When time gating is enabled, it is enabled for all logical input channels. The gate Length is identical for all input channels, but the beginning of the gate time record can be positioned at different locations for each logical input channel (see Time Gating Parameters).
When time gating is enabled, the channel Spectrum traces are derived from the gated time record for the respective logical input channel (Ch1 Gate Spectrum uses Ch1 gate time record, etc.), and the word "Gate" is added to the trace title.
By default, the windowing function used for gated spectral traces is the same as that used for non-gated displays. You can specify a different Window Type for gated spectral traces by clearing Same as Main and selecting a Window Type in MeasSetup > Time > Gate.
When averaging is used on gated measurements:
- RMS and Peak Hold/Continuous Peak Hold averaging are applied to the spectrum display of the gate, while Time averaging is applied to the main time record.
- For RMS and Peak Hold/Continuous Peak Hold averaging, changing any time-gating parameters restarts the average.
The following parameters can be changed without needing to acquire new data when time gating is enabled, averaging is disabled, and the measurement is paused:
- gate delay
- gate length
- resolution bandwidth (ResBW)
- window
The gate can be stepped through the Main Time data in increments by clicking in the Delay field and using the mouse wheel or the up and down arrow keys.
The maximum Main Time Length can be increased by increasing the number of Frequency Points. Alternatively, Auto Frequency Points can be enabled to automatically select the number of frequency points based on the desired Main Time Length.
Resolution bandwidth cannot be independently adjusted in time gating because resolution bandwidth is determined by the length of the time-record, and using Time Gating explicitly sets the length of the time-record.
If using gating to estimate the frequency or phase of a signal at a specific point in time, consider using Analog Demodulation instead. With Analog Demodulation, the instantaneous frequency or phase at a point in time can be measured, rather than the estimate over the gate interval.
After the main time data is acquired, the gate can be repositioned or resized without obtaining new main time data. The VSA will automatically recompute and redisplay the data contained in the modified gate record.