title: FFT output to PSD
body: <p>I need some help understanding the output of the FFT.</p>
  
  <p>I'm working with GNU radio. I have a Signal source with output is Float type, after go through FFT transform, data will be send to my App using UDP.</p>
  
  <p>My App receives the data in a byte array and then converts it into float array. So now I got the FFT output complex with format:</p>
  
  <p>floatArr = {real,img,real,img .....}.</p>
  
  <p>Then I calculate the PSD value from FFT output, and render chart. </p>
  
  <p>But the problem is that my chart is incorrect, totally different for what GNU display</p>
  
  <p>Here my GNU diagram</p>
  
  <p><img src="https://i.stack.imgur.com/qz1pg.png" alt="enter image description here"></p>
  
  <p>I calculate the PSD value with this formula;</p>
  
  <p><strong>1:</strong> Magnitude = 2*sqrt(re^2 + img^2)/N</p>
  
  <p><strong>2:</strong> PSDx = 10*Log10(Magnitude^2)</p>
  
  <p>But my chart look completely different from GNU:</p>
  
  <p><img src="https://i.stack.imgur.com/G5flG.png" alt="enter image description here"></p>
  
  <p>Please help, I currently have very little knowledge of FFT/PSD (and English too). I've tried to render this chart for weeks, actually I just blindly apply formulas.</p>