Also known as: fast Fourier transform, FFT

The fast Fourier transform (FFT) is an efficient algorithm for computing the discrete Fourier transform, reducing the work enough to run many times a second in real time.¹

The FFT computes the spectrum efficiently, splitting the band into equal frequency bins — the basis of the waterfall.

How it works

It splits the captured bandwidth into a number of bins (the FFT size); resolution ≈ sample rate ÷ FFT size. More bins give finer resolution but slower updates and more CPU.

Relevance to SDR

The FFT drives the spectrum and waterfall displays used to find signals and spot a steady control channel.

Sources

1. Fast Fourier transform — Wikipedia, for the algorithm and its efficiency over the direct DFT. ↩

See also

• Fourier transform
• Bandwidth
• Sample rate
• IQ data

Learn it step by step

• The FFT & reading a waterfall

From the blog

• SDR Internals, Part 8: Equalization, diversity & the FFT