The digital dual mode VOR indicator is a digital aircraft navigational instrument intended to replace the current dial or needle type VOR indicators. The new indicator has two modes of operation. In the first mode the instrument functions like a conventional omni while during the second mode of operation the VOR indicator constantly reads out the plane's bearing from the VOR station. The bearing information is displayed in a large three numeral, lighted, digital display. The invention covers the electronic circuitry to provide the digital readout.
4069412 - Area navigation system - Owned by Air Data, Inc. (Worthington, OH) [*] Notice:The portion of the term of this patent subsequent to December 17, 1994 has been disclaimed.
There is disclosed an area navigation system including signal averaging and lag compensation circuits to overcome VOR signal propagation instabilities and a meter sensitivity control circuit which decreases the sensitivity of a track angle deviation left-right needle display as the aircraft approaches a waypoint. Means are also provided for digitally displaying the aircraft bearing to the waypoint.
A display device particularly suited for providing the pilot of an aircraft with combined inflight attitude, heading, altitude, and horizontal situation information previously available only by using two or three devices providing separate displays. The preferred embodiment of this invention combines a commonly used and commercially available flight director-type device for providing a display in combination with a miniature aircraft supported for angular displacement from a vertical orientation to indicate heading error, or heading offset, and an extended course deviation indicator bar which projects into juxtaposition with the miniature aircraft for providing a true picture of the aircraft's horizontal situation relative to a selected VOR, ILS, or MLS course.
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.
