Creating a Multi-VST System

Use the NI-RFSA and NI-RFSG drivers to configure a Multi-Channel Phase-Coherent system with NI VST.

Note Multi-VST systems were first implemented in 2024 Q2.

Configuring a PXIe-5842 Multi-VST System

You can create a multi-VST system with the PXIe-5842.

Use cables to connect the following items:
  • Multiple PXIe-5842 devices
  • A PXIe-5655 device
  • SMA power splitter x2
    Note The splitter size depends on the number of VSTs in the system.

Connect the PXIe-5655 LO OUT for RF IN and RF OUT to a splitter that distributes to the LO IN of each PXIe-5842 device in the system. The LO distribution through the splitters must have a loss between 0 dB and 9 dB for the frequency range of 1500 MHz to 7200 MHz.

For clock cables, attach the REF OUT connector of the primary PXIe-5842 directly into the REF IN connector of the downstream PXIe-5842. Repeat this action for each remaining VST.

For an example of an x2 system using this configuration, refer to the following cabling diagram.



Configuring the Multi-VST System Software

After physically connecting the multi-VST system, you must programmatically configure and calibrate the system.

Use NI Hardware Configuration Utility to associate the PXIe-5655 with each connected VST. For more information on using this product, refer to the NI Hardware Configuration Utility User Manual.

Note Because this configuration associates a single PXIe-5655 with multiple devices, NI Hardware Configuration Utility will display a warning. Click Continue to ignore the warning.
The following installed LabVIEW examples demonstrate how to configure the system software:
  • C:\Program Files\NI\LVAddons\rfsg\1\examples\instr\niRFSG\RFSG Synchronization (NI 5842 Multi-VST Configuration).vi
  • C:\Program Files\NI\LVAddons\nirfsa\1\examples\instr\niRFSA\RFSA Synchronization (NI 5842 Multi-VST Configuration).vi
  • C:\Program Files\NI\LVAddons\vstcalapi\1\instr.lib\niVST\Calibration\ExternalCal\Public\5842\NI 5842 Multi-VST Configuration Self Cal.vi
Note Multi-VST configuration does not support Multi-Span Spectrum or List Mode.

Specifying the Clocking Configuration

To run the devices in this configuration, set the reference clock so that all downstream devices have the correct clock. On the master session, where the PXIe-5842 receives its reference clock from the PXIe-5655, complete the following tasks:

  1. Set the PXIe-5655 reference clock source and rate.
  2. Connect the reference clock export to the RefOut output.
  3. Set the reference clock export rate to 1 GHz.


In the slave sessions, where the PXIe-5842 is downstream of the master session, complete the following tasks:

  1. Set the reference clock source to RefIn input.
  2. Set the reference clock rate to 1 GHz.
  3. For other downstream devices, ensure the slave session is exporting its ref clock to RefOut at 1 GHz. The PXIe-5842 will only accept a 1 GHz reference clock rate.


Self-Calibrating the Multi-VST System

To run a system self-calibration to account for power loss, use the Multi VST Self Cal.vi.

This VI will self-calibrate each VST and reconfigure the output power of the LO to overcome the splitter loss. This calibration data is then set on the device and will persist until a regular self-calibration session is run.

Rerun a regular self-calibration after disassembling this system so the LO power can be set back to normal. The Cal Step control allows the VI to run only the LO target power.
Note As a best practice, run the All calibration step every time. Perform an advanced optimization by running LO calibration once during system creation then run the Self Cal Only calibration step.

Common Multi-VST Issues

Multi-VST systems may experience certain issues.

The following table displays likely problems and solutions.

Problem Solution

The device loses the upstream reference clock and causes the PLL to unlock.

Use NI Hardware Configuration Utility to reset the device and any other downstream devices.

Note As a best practice, leave the 1 GHz ref clock exporting at all times.

An IFIFO timeout error occurs during a RFSA or RFSG reset.

The device clock was disconnected. To resolve the issue, restart the controller.