Claude R. DeBord - Independence MO
Wilcox Electric, Inc. - Kansas City MO
A VOR monitor employs a microprocessor-based system in which, after initial analog detection of a transmitted VOR signal, the critical parameters of the signal are extracted by digital signal processing to ensure that the transmitted signal in space remains within tolerance. Initial processing to isolate the 30 Hz AM (variable) modulation component and the 30 Hz reference component is conducted in the time domain. The 30 Hz reference is recovered by FM quadrature demodulation which, as a by-product, yields data from which an rms calculation is made of the amplitude of the 9960 Hz subcarrier. Further digital processing is then conducted in the frequency domain to yield spectra from which critical parameters of the VOR signal are extracted, e. g. the phases of the 30 Hz components (determining azimuth), the modulation percentages of the 30 Hz variable and the 9960 Hz subcarrier, and the 9960 Hz FM deviation ratio. The identification tone of the transmitted VOR signal is recovered separately from the digital data by application of the Goertzel algorithm and verified by an autocorrelation analysis.