Hughes Aircraft Company

Santa Barbara Research Center

Mark E Preiser

Robert J Cinzori

Arthur H Hardy, Jr

Richard A Dye

A method of and apparatus for modulating, demodulating, and ordering independent signals transmitted over a single link provides mux-demux capability by asymmetric average interpulse spacing so that the information will be received only by the proper listening station despite interruptions or errors in transmission. In the two signal embodiment, a master oscillator provides an asymmetric carrier pulse train to a pair of ramp generators, one leading pulse edge triggered and the other trailing edge triggered. The ramps pulse position modulate the signals by means of a pair of comparators. The modulated outputs of the comparators are applied to an OR gate which combines the pulses to provide a time division multiplexed stream of modulated data having an asymmetric average interpulse spacing. The data stream is transmitted over a pulsed data link to a pair of synchronizers, each of which contains a phase-locked loop having a voltage controlled oscillator whose free running pulse repetition frequency is one-half that of the multiplexed stream and whose loop filter high frequency cutoff is considerably below the lowest modulation frequency. A flip-flop correlator compares the average start times of the voltage controlled oscillators of the two phase-locked loops to provide the control signals for a steering network which directs each of the signals to the proper listening station, assuring the independence of the transmissions.

Apparatus and method for ordering independent signals

A multi-channel adaptive threshold circuit usable to extract affirmative detection impulses from a plurality of detection circuits each having a different background noise level. The circuit comprises a plurality of analogous detection circuits whose outputs are coupled in parallel between a threshold circuit and threshold activation device such as a switch which grounds all outputs when in the ON position. The input to each detection circuit, which is a composite of sporadic affirmative return pulses and continuous background noise, is passed through a unidirectional conducting device, such as a base-to-emitter junction of a transistor, to charge a capacitor to a value which is a function of the continuous background noise. When the threshold activation device is turned off, the output plate of the capacitor of each detection circuit is applied to a fixed threshold circuit. Since a large value resistor coupled between the input plate and ground prevents rapid discharge of the capacitor, the potential across the plates remains substantially constant. The slow discharge results in a higher voltage on the input plate which causes the base-to-emitter junction to be back biased and thus nonconductive for almost all detection signal levels except high voltage pulses which are likely to indicate a positive detection return. Thus, each channel independently sets its own threshold level which is determined by the additional charge due to background noise across the capacitor just before the threshold activation switch is turned off. The signal threshold level in each detection circuit is then the sum of the additional potential across the capacitor of that detection circuit and the fixed threshold voltage established by the threshold circuit.

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Santa Barbara, CA, United States of America

Mark E Preiser