Synthetic doppler direction finder for use with FSK encoded transmitters
First Claim
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1. An improved radio direction finder, comprising, in combination:
- antenna means for receiving a locator transmission signal having alternating periods of a broadcast RF carrier wave and a broadcast FSK code modulated RF carrier wave;
radio direction finder (RDF) means coupled to the antenna means for determining the direction to a broadcasting transmitter and for extracting FSK coded information coded into the locator transmission signal by the broadcasting transmitter; and
wherein the RDF means comprises antenna virtual rotation control means coupled to the antenna means for controlling the antenna in both a non-rotational mode for detection of the broadcast FSK code modulated RF carrier wave and a virtual rotation mode for detection of the broadcast RF carrier wave.
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Abstract
A radio direction finder based on the simulated Doppler frequency shift principle is disclosed that is applicable to FSK encoded pulsed transmissions. Typical applications include tracking of stolen vehicles or shipped package tracking. During FSK decoding, all antenna elements of the antenna array are turned on in a non-rotating mode thus eliminating error due to the simulated antenna rotation modulation while providing enhanced gain for the FSK decoder circuit. After decoding a suitable FSK signal, a virtual antenna rotation is enabled, and the bearing is measured during the time interval when the transmitter is only broadcasting a carrier wave.
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Citations
21 Claims
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1. An improved radio direction finder, comprising, in combination:
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antenna means for receiving a locator transmission signal having alternating periods of a broadcast RF carrier wave and a broadcast FSK code modulated RF carrier wave; radio direction finder (RDF) means coupled to the antenna means for determining the direction to a broadcasting transmitter and for extracting FSK coded information coded into the locator transmission signal by the broadcasting transmitter; and wherein the RDF means comprises antenna virtual rotation control means coupled to the antenna means for controlling the antenna in both a non-rotational mode for detection of the broadcast FSK code modulated RF carrier wave and a virtual rotation mode for detection of the broadcast RF carrier wave. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A method for receiving and decoding a locator transmission signal, comprising, the steps of:
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providing an antenna for receiving the locator transmission signal wherein the locator transmission signal comprises; a period of a broadcast RF carrier wave; and a period of a broadcast FSK code modulated RF carrier wave, wherein the FSK modulation is performed by a broadcasting transmitter; holding the antenna stationary for enhanced extraction of FSK code embedded information from the broadcast FSK code modulated RF carrier wave; and virtually rotating the antenna during the period of the broadcast RF carrier wave for determining the bearing angle to the source of the broadcast RF carrier wave. - View Dependent Claims (20, 21)
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Specification