An analogue computer for Fourier transforms

The paper gives the basic principles of a computer for obtaining a graphical display of the Fourier transform of a function which can be represented by a finite number of ordinates over a finite range of the input variable. A delay line with linear phase-shift/frequency response is used to give the exponential term in the transform, and a time-variation of carrier frequency in sympathy with the time-base of the display unit gives the required variation of the index of this term.