Frequency Mask Trigger Style (Trigger)
The trigger style is a frequency-selective trigger that triggers an acquisition based on spectral events that meet particular criteria with respect to a user-defined frequency mask.
When connected to an instrument that supports frequency mask triggering (FMT), the VSA enables as a valid trigger style and shows the FMT-specific controls in the section of the dialog.
Clicking the button opens the FMT Editor which is used to create and modify the frequency masks. The other properties are used to control the operation of the trigger, independent of the mask(s) shape.
Additionally, certain traditional Trigger properties (Trigger Delay and Holdoff) can be used to control the Frequency Mask trigger just as any other trigger style. Parameters not compatible with the Frequency Mask trigger style are disabled.
The Frequency Mask Trigger controls will not be shown unless connected to an Keysight X-Series Analyzer with the Real Time Spectrum Analyzer (RTSA) mode.
| Frequency Mask Trigger | |
|---|---|
| Parameter | Description |
| : |
Indicates when the trigger event occurs, based on the overlap of the measured spectrum and the enabled masks (parameter). : The trigger occurs when the spectrum enters a mask. : The trigger occurs when the spectrum leaves a mask. : The trigger occurs if the spectrum is inside a mask. : The trigger occurs if the spectrum is outside a mask. : The trigger occurs after the spectrum enters a mask (either upper or lower) and subsequently leaves a mask. : The trigger occurs after the spectrum leaves a mask (either upper or lower) and subsequently enters a mask. |
| : |
Specifies which of the masks are actually used by the trigger. The choices are "Upper," "Lower," or "Both." An FMT definition can have an upper and/or a lower mask. These masks can be defined independent of whether they are actually used by the trigger or not. |
| : |
Specifies the time window that is applied by the instrument's FMT measurement before calculating the spectrum of the signal. Note that this window is independent of the window type being used by the VSA. Beware that changing the window type of the instrument's FMT measurement can radically alter the shape of the spectrum calculated and used by the trigger. It is unlikely that a mask defined for one window type will trigger as expected when a different FMT window type is used. |
| : |
This property is used to specify the resolution bandwidth (RBW Resolution Band Width (RBW or ResBW): specifies the minimum frequency bandwith that two separate frequency spectra can be resolved and viewed seperately. For FFT (digital) based VSA's the process is equivalent to passing a time-domain signal through a bank of bandpass filters, whose center frequencies correspond to the frequencies of the FFT bins. For a traditional swept-tuned (non-digital) spectrum analyzer, the resolution bandwidth is the bandwidth of the IF filter which determines the selectivity.) used by the instrument's FMT measurement when searching for a frequency trigger event. When is selected, the RBW is chosen by the hardware (and this value is shown in the text box in the tab). When is cleared, the VSA sets the instrument's FMT RBW to the specified value. The VSA will constrain the value you specify to a RBW value supported by the hardware. All RBW/ResBW values shown on the VSA's user interface are the Equivalent Noise Bandwidth (ENBW) of the frequency-domain filter defined by the window type selected and the window length. This is different from RBW values shown on X-Series Signal Analyzers' front-panels, which typically show the 3 dB bandwidth of the window. |
| : |
The shifts the upper/lower mask in frequency by the specified amount. See Using Frequency and Amplitude Mask Offsets. |
| : |
The shifts the upper/lower mask in amplitude by the specified amount. See Using Frequency and Amplitude Mask Offsets. |
To make the VSA's spectrum best match the spectrum used by the FMT hardware for triggering, set the VSA's ResBW and Window Type to match the corresponding settings on the tab, and set the Frequency Points to 801.
Trigger Location
The frequency mask trigger works by taking overlapped FFTs of the input time data and checking the spectrum from each FFT Fast Fourier Transform: A mathematical operation performed on a time-domain signal to yield the individual spectral components that constitute the signal. See Spectrum. against the FMT masks and criteria. When an FFT block meets the FMT criteria, the instrument triggers an acquisition and sends the data, starting at the beginning of the FFT block that contained the trigger event, to the VSA.
When the trigger event happens, the instrument will send a Trigger Out signal. If you are using the Trigger Out from the FMT instrument to trigger another instrument's acquisition, you will need to add some pretrigger delay to the externally triggered instrument to ensure the data at the beginning of the FFT is captured by the second instrument.
See Also
