Sanders Associates Limited

Lucent Technologies Inc.

Solar Decisions, Inc.

William C Wurst

Lester R Brodeur

William R Mercer

Donald W Fyfe

A low-cost monitor includes two comparators which are adapted to form a window comparator which frames a laser transmitter's normal range of operation. An apparatus for generating an amplified back-face-monitor voltage corresponding to the laser transmitter's optical output power level is coupled to the window comparator. A reference voltage is also coupled to the window comparator which defines the upper threshold of the normal operational range. A controllable variable voltage source is coupled to the window comparator and is used to define the lower threshold of the normal operating range, where this lower threshold has two associated threshold values as described above. The lower threshold is initialized to the first threshold value which corresponds to an end-of-life operating state of the laser transmitter. When the back-face-monitor voltage signal equals or drops below the first threshold value, an alarm signal is generated by the laser monitor, and the controllable variable voltage source is switched to a second state for providing a second threshold value which corresponds to failed operating state of the laser transmitter. As the optical output power level continues to decline with temperature and time, it eventually falls belows the second threshold and a second alarm is generated to indicate failure of the laser. A variable gain instrumentation amplifier is coupled to the generating apparatus and utilized to measure the optical output power of the laser transmitter.

Method and apparatus for monitoring performance of a laser transmitter

A temperature differential measuring circuit includes first and second temperature sensitive transducers disposed in corresponding first and second legs of a bridge circuit. Disposed in third and fourth legs of the bridge circuits are fixed resistors. An operational amplifier has its input terminals connected to the output terminals of the bridge circuit with its output terminal connected to one of the fixed resistors so that that fixed resistor is in feedback relation between the input and output of the amplifier. The transfer function of this bridge circuit is less temperature dependent than the transfer functions of conventional voltage bridge circuits.

Temperature sensing

A Loran-C navigation receiver is disclosed wherein digital circuitry and a microprocessor is used to automatically identify Loran transmitting stations and makes standard hyberbolic navigation measurements. The receiver operator manually enters a group repetition rate into the apparatus being operated. Initially, the receiver receives and analyzes all received signals until signals from a master and secondary station are received regularly at the stored group repetition rate. The apparatus then changes to a fine search mode in which the exact time of receipt of the master and secondary station signals is determined; the phase code of the received signals is checked to determine if the received signal is a ground or sky wave, and a determination is made if there is a deflective secondary station blink code. The time difference of arrival measurements are then made and an output provided to be plotted in a well-known manner on a Loran-C chart to locate the position of the craft upon which the receiver is located.

Loran-C navigation apparatus

A Loran-C receiver cycle detector is disclosed which processes Loran-C signal pulses on a cycle-by-cycle basis of the carrier frequency and generates an output for a specific carrier cycle. Due to received noise, sampling techniques are used to create a histogram which is analyzed to provide feedback used to accurately locate a tracking point on each Loran-C pulse.

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Amherst, NH, United States of America

William C Wurst