Triggering the VNA using SCPI

To understand how to trigger the VNA using SCPI, it is very important to understand the VNA trigger model. Here is a very simple explanation. These three separate functions control VNA triggering:

1. Trigger:Source - Where the trigger signals originate:

   • Internal Continuous

   • Internal Manual (Single)

   • External - a trigger source that is connected to the VNA rear panel.

2. Trigger:Scope - what gets triggered:

   • Global - each signal triggers all channels in turn.

   • Channel - each signal triggers ONE channel.

3. Channel settings (Sense<ch>:Sweep:Mode) How many triggers will each channel accept before going into hold.

   • HOLD - channel will not trigger.

   • CONTinuous - channel triggers indefinitely.

   • GROups - channel accepts the number of triggers specified with the last SENS:SWE:GRO:COUN <num>.

   • SINGle - channel accepts ONE trigger, then goes to HOLD.

   • Point trigger   SENS1:SWE:TRIG:POINt

When controlling the VNA using SCPI, a SINGLE trigger is used to ensure that a complete sweep is taken. This example demonstrates how to Single trigger the VNA using the following two methods:

• Simplest Triggering  

• • This method uses the default Trigger Source = Internal to send a stream of trigger signals.

  • The channel is configured to ACCEPT only a single trigger signal, then HOLD (Sense<ch>:Sweep:Mode SINGle). This is the ONLY required command.

  • This method can also be used when an External trigger source sends a continuous stream of trigger signals.

• Advanced Triggering

• • This method SENDS a single trigger from the Source, which can be from either Internal (using INIT:IMM) or External triggering.

  • Each channel is configured to accept an unlimited number of triggers. This method is the only way to perform point triggering.

  • When you require some channels to accept continuous triggers and other channels to accept single triggers, see INIT:IMM Advanced to learn how.

The SCPI commands in this example are sent over a COM interface using the SCPIStringParser object. You do NOT need a GPIB connection to run this example.

This VBScript (*.vbs) program can be run as a macro in the VNA. To do this, copy the following code into a text editor file such as Notepad and save it on the VNA hard drive as Trigger.vbs. Learn how to setup and run the macro.

Measurement setup example:  This section of code can be used at the start of both methods. It sets up:

• S11 traces on two channels

• 10 data points

• Sweep time of 2 seconds - this is slow enough to allow us to watch as each trace is triggered.

Simple Triggering  The following example sends a continuous stream of trigger signals and each VNA channel is set to ACCEPT only a signal trigger signal, then HOLD.

• This example can be used to configure External triggering where the trigger source sends a continuous stream of trigger signals. Configure the type of trigger signal that the VNA responds to using the CONTrol:SIGNal command. The command in this example sets the VNA to respond to HIGH TTL signals at the rear-panel BNC1 trigger IN connector. This command also automatically sets Trigger Source to External Trigger.

• The TRIG SCOPE (Global or Channel) setting is NOT necessary with a continuous stream of trigger signals. The example program directly controls when each channel is triggered.

• Point triggering can NOT be used with a continuous stream of trigger signals because in point triggering the channel will accept as many triggers as necessary to complete ONE full sweep. Use the single SEND example for point triggering.

Advanced Trigger This example section performs Single Send triggering. Here, single triggering is accomplished by SENDING one trigger signal from the Trigger source and each channel is setup to accept unlimited trigger signals. See the INIT:IMM command for more details.

• Using this method, it is possible to change Trigger:Scope to Global or Channel. Set trigger scope to channel if there is some code to execute between channel measurements. Similarly, this method can be used to set Point triggering. Use this method if there is some code to execute between data point measurements.

• In addition, this method can also be used to perform External triggering if the external trigger source is capable of SENDING single triggers. See the CONTrol:SIGNal command to set the type of signal to which the VNA will respond.

• If the external source can only send a continuous stream of trigger signals, then the Single Accept section must be used.

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