Clarifications on amplitude normalization values

Discussion in 'XeThru Embedded Platform (XEP)' started by vrudakova, Jan 5, 2019.

  1. vrudakova

    vrudakova New Member

    Hello,

    I was looking at the Matlab example "XEP_X4_plot_frame.m" and used it with a presence module (X4M300) that I have. When testing, I ran it in the no-profile mode. When I look at the code, the conversion from IQ to baseband is done the following way:

    frame = frame(1:end/2) + 1i*frame(end/2 + 1:end);
    ph.YData = abs(frame);

    And then it is plotted using the next limits:

    ylim([-0.01 0.1]);

    In the other thread https://www.xethru.com/community/threads/why-amplitude-of-baseband-is-so-small.331/ it is mentioned the amplitude max should be 1.4. Did I understand it right? In this case, how come the result baseband data (which is calculated as shown above) is plotted using the upper limit of 0.1? Moreover, when I tried to run the code, I noticed the amplitude values are rarely go above 0.01. Even the XethruExplorer shows amplitude with max value of 0.01.

    Would be nice if someone could clarify why it is said the amplitude is normalized up to 1.4 while the display values are so small. Is it due to the nature of the radar technology and it represents the amount of signal received? Is it a common practice to normalize the amplitude again to, let's say, 0.02 so that to get signal between [0,1]?

    Thanks,
    Victoria
     
  2. Charlie Shao

    Charlie Shao Moderator Staff Member

    Hi Victoria,
    The amplitude signal varies with the reflection signal. The theoretical max value is 1.414(I =1, Q=1). If you place a metal plate in front of the sensor, you will get a high amplitude. Depends on your application, you can choose a maximum amplitude value to normalize your radar data.
     
  3. vrudakova

    vrudakova New Member

    Charlie, thanks for clarification, makes sense now.