FFT output to PSD

Asked Sep 13 '16 at 04:05

Active Sep 14 '16 at 12:40

Viewed 606 times

I need some help understanding the output of the FFT.

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.

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:

floatArr = {real,img,real,img .....}.

Then I calculate the PSD value from FFT output, and render chart.

But the problem is that my chart is incorrect, totally different for what GNU display

Here my GNU diagram

enter image description here

I calculate the PSD value with this formula;

1: Magnitude = 2*sqrt(re^2 + img^2)/N

2: PSDx = 10*Log10(Magnitude^2)

But my chart look completely different from GNU:

enter image description here

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.

edited Sep 14 '16 at 12:40

SleuthEye

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asked Sep 13 '16 at 04:05

Bihex_26

Not really a programming question - more likely to get good answers on http://dsp.stackexchange.com ? – Paul R Sep 13 '16 at 07:18
Many thanks, i hasnt found my answer yet, but this look promising. – Bihex_26 Sep 13 '16 at 09:00
In your second image, which is GNU Radio and which is your plot? – Ahmed Fasih Sep 13 '16 at 12:45
@Ahmed Fasih the one with title"Top Block" is GNU radio – Bihex_26 Sep 14 '16 at 02:28
HAve a look at https://stackoverflow.com/questions/51784385/calculating-snr-using-psd-of-captured-signal-and-noise – Edward Kigwana Jan 12 '20 at 19:25

FFT output to PSD

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