8 Trigger
8.3 Gate Settings
signal at the Gate Source.
This form of gating may be thought of as a simple switch, which connects the signal
to the input of the spectrum analyzer. When the gate conditions are satisfied, the
switch is closed, and when the gate conditions are not satisfied, the switch is open.
So we only look at the signal while the gate conditions are satisfied.
With this type of gating, you usually set the instrument to sweep very slowly. In fact,
a general rule is to sweep slowly enough that the gate is guaranteed to be closed at
least once per data measurement interval (bucket). Then if the peak detector is
used, each bucket will represent the peak signal as it looks with the gate closed.
FFT
In FFT gating, when Gate is ON, an FFT is performed whenever the gate conditions as
specified in the Gate menu are satisfied by the signal at the Gate Source. This is an
FFT measurement that begins when the gate conditions are satisfied. Since the time
period of an FFT is approximately 1.83/RBW, you get a measurement that starts
under predefined conditions and takes place over a predefined period. So, in
essence, this is a gated measurement. You have limited control over the gate length,
but it works in FFT sweeps, which the other two methods do not.
Gated FFT is not possible in zero span since the instrument is not sweeping, so in
zero span the Gated LO method is used. Data is still only taken while the gate
conditions are satisfied, so the gate settings do impact when data is acquired.
The Gate Length will be 1.83/RBW.
This is a convenient way to make a triggered FFT measurement under control of an
external gating signal.
8.3.6 Control Edge/Level
Sets the method of controlling the gating function from the gating signal.
EDGE
The gate opens (after the Delay) on the selected edge (for example, positive) of the gate
signal and closes on the alternate edge (for example, negative)
LEVel
The gate opens (after the Delay) when the gate signal has achieved a certain level and
stays open as long as that level is maintained
Remote Command
[:SENSe]:SWEep:EGATe:CONTrol EDGE | LEVel
[:SENSe]:SWEep:EGATe:CONTrol?
Example
:SWE:EGAT:CONT EDGE
Dependencies If the Gate Method is FFT, this control is grayed-out and EDGE is selected
If the Gate Source is TV, Frame, or Line, this control is grayed-out and EDGE is selected
2489 Vector Modulation Analyzer Mode User's &Programmer's Reference
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