Fast and Accurate Frequency Meter Using the Interpolated DFT Method

The Interpolated DFT is a non time-consuming supplement to the DFT algorithm. It allows to achieve a much greater frequency measurement accuracy than the DFT and is easily applicable to multitone spectrums. A very simple variant of the Interpolated DFT, proposed and analyzed in previous papers, was implemented in the frequency meter. The introduced device allows to check the correctness of the theoretical limitation and simulation results obtained earlier. The instrument is based on a microcontroller with a DSP unit and a 14-bit fast AD converter. The actual properties of the meter were introduced in the paper. The accuracy of the frequency measurement, the influence of the number of samples in a series and the influence of measured signal amplitude variation during acquiring a series of samples on the accuracy are consistent with the theoretical limits and simulation results with one exception. A boundary of the accuracy of frequency measurement related to used single-precision floating point format occurred. The limiting parameters of the introduced meter are: rate of measurements up to 410 per second and standard deviation about 7.6·10-8