Measuring Phase Noise With RFmx

This article provides some general information about the RFmx Phase Noise measurement which runs inside the RFmx SpecAn personality and includes step-by-step instructions on how to take a Phase Noise measurement including the tuning of the settings.

Requirements:

• NI-RFSG driver

• NI-RFSA driver

• RFmx Phase Noise

The oscillators that are present in any RF communication system have several impairments, where Phase Noise is part of that list. The RFmx Phase Noise software application extends the capability of NI RF instrumentation for phase noise analysis and helps to measure log plots and spots, and integrated them. You also can perform and debug measurements with interactive soft front panels and this can be combined with the RFmx Waveform Creator to create a playback open, unlocked waveforms and speed up automated testing with the API.
NI-RFmx contains several supported personalities in InstrumentStudio for use with RF Signal Analyzer panels, and below you will find the list with a link to the licensing information for each one:

• RFmx SpecAn (the personality we will be using in this article)

• GSM (EDGE+)

• LTE / LTE-Advanced

• NR

• TD-SCDMA

• W-CDMA (HSPA+)

• Bluetooth

• WLAN

A more in-depth explanation of Phase Noise can be found in the following online help topic: Phase Noise
Note: The Phase Noise measurement requires license activation. If you install RFmx SpecAn but do not activate the Phase Noise measurement license, you will have 30 days from the first time you use the measurement to evaluate it. Subscription license information can be found in the following link: RFmx Phase Noise Licensing information.

 The steps for performing a Phase Noise Measurement are the following:

• • Open the RFmx Soft Front Panel (starting on version 2022 Q3 of RFmx the Soft Front Panel will be integrated with Instrument Studio) for the Analyzer that you are using and click on Add/Remove and select Phase Noise to open the layout for the Phase Noise Measurement:

    

  • Once the layout changes to the Phase Noise Measurement, set the center frequency, reference level, and start and stop frequency. For this example, we will use 1 GHz, 13 dBm, 100 Hz, and 1 MHz respectively:

    

     

  • In those settings, the RBW Percentage specifies the RBW as a percentage of the start frequency of each subrange or decade so it will change if you move up.

  • Configure the Y axis to adjust the display properly:

    

For this example, we are using a PXIe-5644 connected in a loopback test and the settings for the generated tone are shown in the following screenshot:

After configuring the RFmx SFP as shown above, the result will be something like the following screenshot which shows the power level for the frequency specified on the Spot Noise Frequency List:

The RFmx driver installs some examples by default including the RFmxSpecAn PhaseNoise (Basic) that can be found in the following location: C:\Program Files (x86)\National Instruments\LabVIEW 2022\examples\RFmx\SpecAn (this location may vary depending on your LabVIEW version and bitness).
After configuring the settings just as we did above and running that example, the result is shown in the following screenshot:

Next Steps

You can find the instructor video for the RFmx Phase Noise measurement in the Measuring Phase Noise with NI-RFmx lesson from the Introduction to RF Signal Generation Acquisition and Analysis with NI RF Technologies online training.