How to convert fft plot into PSD(Normalized) vs Freqeuncy (Hz)

KlausST said:

Hi,

X-axis:
You see it is a logarithmic scale. You need to start with a frequency larger than 0Hz (0Hz = DC is not possible)
In the top picture this is 1000Hz, in all other pictures it is 100Hz.
But this is somehow untypicial for an FFT output. An FFT output always starts with 0Hz (=DC) and has 2^n frequency taps with equal frequency distance. It is linear, not logarithmic.

Example: An FFT result of 1024 values sampled at 10.24kHz will give 512 results stating with 0Hz and an equal frequency distance of 10Hz = 10.240 Hz / (2 x 512)

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Y-Axis.
Often this is in a dB scale.
In your top picture you see the referece signal. It is "normalized" to be in scale of "1" wich is 0dB.

I can´t see how the other diagrams are normalized. I expect either a reference signal (value = 1 or 0dB) or a fixed power like "1mW" which is 0dBm. But both is missing. Maybe they refer to the first diagram.

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Klaus

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