International Telemetering Conference Proceedings / October 29-November 02, 1990 / Riviera Hotel and Convention Center, Las Vegas, Nevada / The Fast Fourier Transform (FFT) converts digitally sampled time domain data into the frequency domain. This paper will provide an advanced introduction for the telemetry engineer to basic FFT theory and then present and explain the different user preprocessing options that are available when using the FFT. These options include: using windowing functions, “zero filling” for frequency data interpolation, and setting the frequency resolution of the FFT resultant spectrum,