Square wave FFT results show frequency that seems too low?

1. What is the FFT of a square wave?
2. How do you find the frequency of a square wave?
3. Which harmonics are not available in the FFT frequency spectrum of a square wave with 50% duty cycle?
4. How do you choose a sampling frequency in FFT?

What is the FFT of a square wave?

In the frequency domain, the overall average of a signal is its content at DC or 0Hz -- so that's why there's a peak at 0Hz. The FFT of a square wave that is centered on 0V has energy at every odd harmonic, starting at 1.

How do you find the frequency of a square wave?

Here, T is the period of the square wave and f is its frequency, which are related by the equation f = 1/T.

Which harmonics are not available in the FFT frequency spectrum of a square wave with 50% duty cycle?

These particular harmonics are missing from the square wave because of its duty cycle . A duty cycle is the percentage of the waveform that occurs above the zero axis. The duty cycle of a square wave is always 50%, or 1/2. Because the duty cycle is 1/2, every second harmonic is not present.

How do you choose a sampling frequency in FFT?

The frequency resolution is equal to the sampling frequency divided by FFT size. For example, an FFT of size 256 of a signal sampled at 8000Hz will have a frequency resolution of 31.25Hz. If the signal is a sine wave of 110 Hz, the ideal FFT would show a sharp peak at 110Hz.