Digital Marine Electronics Corporation

Otis Philbrick

Jeffrey M Morris

Sheldon B Michaels

In a Loran Receiver that receives radio frequency (RF) signals from a master beacon and at least two slave beacons (also called secondary transmitters) and converts the received signals into hyperbolic coordinates that locate the position of the receiver with respect to the beacons and a programmed computer controls modes and sequences of operation of the system, these modes being generally the beacon pulse search mode, front edge/zero crossing location mode and the zero crossing track mode, received beacon pulses are searched and identified by the following technique: all received signals are repeatedly sampled at the beacon group repetition interval (GRI) in a regular sampling pattern in which the sampling rate is greater than the beacon pulse rate, each sample interval being only a small portion of a beacon pulse RF excursion; the samples are hard limited and assigned a value of plus or minus, depending upon whether they exceed a threshold, and these plus-minus patterns are accumulated over many GRIs and stored; the stored accumulation is analyzed according to the computer program and compared with a reference pattern; and when there is correlation within programmed conditions, the front edge/zero crossing location mode is then pursued to locate the samples at the zero crossing of a particular RF excursion of the tracked beacon pulses.

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Westwood, MA, United States of America

Otis Philbrick