VSS RF Inspector (RFI) can be used for viewing the spectrum of an RF system. Signal heritage is one of the more important aspects of the RFI analysis. With mouse-click and hold on any of the spectral components from the RFI_PWR_SPEC, RFI_V_SPEC or RFI_I_SPEC measurements, information on that spectral component is displayed as shown here:
By double-clicking on the spectral component, the RFI dialog box is opened
In the Heritage window pane, the individual contributors for a particular spectral component are displayed. More information on the RFI dialog box can be found in this link.
When working with mixers, one of the more important contributors to track are the M, N harmonics that satisfy the mixer equation:
M*Finput + N*FLO = FIF
The M,N information is contained in the heritage window data, but there may be a need to organize the data differently such that the M,N harmonics are more readily apparent.
The data from the Heritage window can be exported as an XML file. Using Python, the XML data can then be parsed and then written to an Excel compatible file format.
Python must be installed, see this link for installation. Three additional Python modules are also required: lxlm for reading and parsing xml files, openpyxl for writing Excel compatible files, and win32com for controlling Excel application. win32com is available from the pywin32 package. When using the Anaconda distribution package, see this link for installation instructions. Otherwise pip can be used for installation:
pip install lxml pip install openpyxl pip install pywin32
Download and extract the RFI_Mixer_Heritage_Parser.zip file:
This file contains single Python file: RFI_Mixer_Heritage_XML_Parser.py as well as a sample AWR project file: RFI_Example.emp.
The script is intended for analyzing the M,N mixer harmonics of a single mixer system in VSS. Some guidelines on the System Diagram include:
- The script is only compatible with the RFI_PWR_SPEC measurement under the RF Inspector measurement group. Use the following settings:
- Only a single mixer is allowed in the system. For systems with multiple mixers in the RF chain, you will need to construct a separate system diagram for the analysis of each individual mixer.
- Active elements after the mixer may result in M,N products not being properly analyzed. For best results place the analysis test point immediately after the mixer as shown:
- Modulated sources should not be used. Use PORT_SRC or TONE source. Multi-tone signals are allowed for both the input and LO. Use the TONE source with FRQ set as a vector of frequencies as shown:
Creating the XML File
From a graph containing the RFI_PWR_SPEC measurement, double-click on one of the spectral components to open the RFI dialog box:
In the RFI dialog box, select Export... to bring up the Export Options dialog box
In the Export Options dialog box, use the following settings:
Control the minimum spur level processed using the Export components greater than or equal to setting. Click Export and same the .XML file.
Using the Script
Once the .XML file has been created, you can run the Python script. The script opens a file browser. Navigate to the directory where the .XML file was stored and open the file. Next the script will write an Excel compatible file that uses the same name as the .XML file selected but with the extension changed to .xlsx. Then the script will open the Excel application and then open the .xlsx file within Excel.
The Excel file contains four tabs with various sorting of the spur data. Most spurs have multiple contributors, so for each spur frequency, the individual contributors are also listed.
Sorted by Freq tab show the spurs sorted by spur frequency
Sorted by Power tab show the spurs sorted by spur power level
Spurs Sorted by Order tab shows the spurs sorted by the spur order: spur order = abs(M) + abs(N)
Spurs that are result from multiple mixer input port signals that generate intermodulation distortion product are shown in the Intermods tab