Record Multi-Channel RF Signal to Multiple Files Using PXI VST and LabVIEW

NI RF record and playback system can record multi-channel RF signals to one file or multiple files and can play back the recorded multi-channel signals one channel at a time or all channels at the same time. This article discusses the method of procedure for setting up and operating the multi-channel record and playback system. The intended audiences are PXI VST users who have basic knowledge of RF devices such as combiners, splitters, filters, duplexers, and multiplexers. Refer to What is multiplexers for more details.

As an example, consider a two-channel signal shown below and with the following frequency parameters:

• Center frequency of the two-channel signal: Fc = 2.595GHz
• Center frequency of the left-channel signal: Fcl = 2.535GHz
• Center frequency of the right-channel signal: Fcr = 2.655GHz

System Hardware Set Up

The record and playback system can be set up in two different ways. One way with filter and combiner/splitter, another way with a multiplexer, both are discussed below.

1. Setup System with Combiner/Splitter and Band-Pass Filter.

   1. Set up the system with combiner/splitter and band-pass filter as displayed in the below image.

   2. The band-pass filters and splitter/combiner can be replaced by duplexers or multiplexers if RF loss is a concern.

   3. The filters connected to the combiner are optional.

2. To set up a system with Multiplexer we can choose duplexer as it is the simplest multiplex; the record and playback system with duplexer is shown below:

Record the Two-Channel Signal

1. Launch RFmx Waveform Creator by typing RFmx Waveform Creator in the Search bar next to Start.
2. Select Modulation >> Multi-Carrier.
3. Add the Multi-Carrier file created for the demo system by following the sequence Multi-Carrier >> Add >> Click to select a file >> File name, shown below.

4. Refer to RFmx Getting Started for the details of creating the multi-carrier file. 
5. Select Instrument >> Download & Play, then select Device Name 5646r (depends on which device is used to create the waveform) the Multi-Carrier file created for the demo system from the pop-up menu, select the Center Frequency, select Create & Play to generate the 2 channel RF signal.

 

6. Run LabVIEW as administrator by typing LabVIEW in the Search bar next to Start.
7. From LabVIEW, click on File to Open Project 5840 Streaming Host from C:\Program Files\National Instruments\LabVIEW 2021\examples\NI Streaming\PXIe-5840\Host.

8. Double click on Stream to Disk.vi to run the VI.
9. Select the Device, File path, Data Width, Centre Frequency, IQ Rate, and Data Destination, and click Run to start the recording as shown below:

Playback the Recorded Two-Channel Signal

1. Launch RFSA by typing NI-RFSA Soft Front Panel in the Search bar next to Start.
2. Set up the Centre Frequency and Span according to the recorded signal as shown below:

3. Double click on Stream from Disk.vi to run the vi from project 5840 Streaming Host from C:\Program Files\National Instruments\LabVIEW 2021\examples\NI Streaming\PXIe-5840\Host.

4. Select the Device, File path, Centre Frequency, IQ Rate, Data Source, click Run to start the recording. One example of playing back 2 channels signal shown below:

5. RF Spectrum will be displayed as shown on RFSA Soft Front Panel.

The results shown in Steps are for recording 2-channel signal and playback the recorded 2-channel signal at the same time. The system can be used for recording and playback multiple channel signals and playback the recorded signal one channel at a time or all the channels at the same time.