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Home Caller ID Position-finding-system

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 Position finding system

Details
Inventors: Lowe, Eric; Poppe, Martin C.; Stratton, Andrew;
Assignee: Terrafix Limited (Welyn, GB2)
Primary Examiner: Blum; Theodore M.
Assistant Examiner: Gregory; Bernarr Earl
Attorney, Agent or Firm: O'Connell; Robert F.

Three fixed reference stations having known positions comprise Omega receivers. Phase measurements made at all three stations are assembled at a master station, utilizing landlines or radio links and, using the known positions of the stations, a central processing unit calculates not merely the offset of the master station as measured from the true position but also the errors in the azimuths of the propagation directions of the received signals. The position measurement of a vehicle with an Omega receiver is corrected on the basis of the offset and also the errors in the said azimuths. Sufficient accuracy is achieved for finding the position of land based vehicles whose position may be calculated subject to the corrections in the master station on the basis of raw data transmitted to the master station over a link. Alternatively the azimuth corrections may be transmitted to the vehicle over the link. Two fixed stations suffice if they can measure absolute phase.

DETAILED DESCRIPTION The basis of the invention is that the phase of the field of radio navigation transmitting stations in an area may be completely described by the azimuth angle of the wavefront relative to a geodetic reference such as grid or true north and the local wavelength.
Measurements at three stations situated at known geodetic positions enables the azimuth angles and local wavelength to be determined for any group of the three transmitting stations required for hyperbolic position finding.


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