How To Get Correct MASK When Measuring SEM

Updated Jul 24, 2023

Environment

Software

  • RFmx WLAN
  • RFmx Waveform Creator 

IEEE protocol define the different MASK curve for 802.11 standards when you measured WLAN SEM for different standards; Sometimes you used RFmx tools to measure it , you will see the un-correct MASK on the measurement result. How could you fix the issue ? 

1.Used RFmx Waveform Creator to generate one 802.11n 20MHz signal at center frequency 5.5GHz

802.11n 20MHz.jpg


2.Then used RFmx WLAN to measure the SEM with correct parameters when the VST are loop-back connecting;


RFmx WLAN SEM result.jpg


3.Check the MASK parameters , you will find the limit of offset >30MHz was not correct

mask limit for SEM.jpg


Compare with protocol definition , you will find the difference as below:

MicrosoftTeams-image (46).png


The correct limit of offset > 30MHz is -40dBr , but the RFmx WLAN used un-correct limit ;

4.Check the parameters of WLAN in RFmx WLAN SFP , you will find the parameter of Frequency Band un-correct (default value: 2.4GHz) ;

frequency band of RFmx.jpg


Re-check the SEM result after change the Frequency Band as 5GHz.
 

You can see the correct MASK curve after changing the Frequency Band as 5GHz , like below picture:
 
correct mask with frequency band 5GHz.jpg

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