How can you make the measurement result not change when multiple measurement windows are enabled?

Updated Jun 8, 2023



  • RFmx SpecAn
  • RFmx

When customer used RFmx SpecAn to measure one CW signal(SG setting power as -10dBm) , they found below problems:
1.When he only enabled the "Channel Power" measurement, he see the "Total Carrier Power" was -10.13dBm;
2.When he enabled the "Channel Power" and "Spectrum" at the same time , the result of "Total Carrier Power" is only -9.68dBm.
Why is there the big difference for different measurement windows enabled status ? 

1.When we only enabled “Channel Power” measurement , we can check the LO parameters as below picture :
CHP Only LO setting.jpg

2.When i enabled the "Channel Power" and "Spectrum" at the same time , we re-check the LO setting parameters as below :
CHP with Spectrum LO setting.jpg

We can see there is a difference on the parameters LO Offset and Downconverter Center Frequency;

3.When we set the "Downconverter Frequency" still same value manually when i enable one measurement "Channel Power" and two measurement "Channel Power" and "Spectrum". We can see the measurement result of Total Carrier Power was still no changing; 

CHP with Spectrum measurement with Manually setting LO.jpg

By setting the LO parameter unchanged, we can ensure that the CHP test results do not change depending on whether the "Spectrum" test is turned on or off.