Grumman Aerospace Corporation

Saulius Janusas

Stephen F Piper

James J Hatton

A covert communication system utilizes a series of low level duty cycle coded pulse train transmissions which at the necessary end have signal to noise ratios much smaller than unity. Such transmissions are buried in noise and hence are undetectable by ordinary means. The coded pulse trains do not carry data and their sole purpose is only to be compressed by a code matched correlator into a single large pulse per pulse train. Data are encoded in the timing between adjacent compressed pulses of adjacent pulse trains. The low duty cycle of the pulse trains is used to force an unfriendly receiver, which does not know the code of the pulse train transmissions, to integrate its own receiver noise into its detection circuits, thus making the transmissions even less detectable.

Covert communication system

A covert communication system uses ultraviolet light rather than radio waves as a medium for communication. Suitable wavelengths are chosen by examining atmospheric penetration, attenuation by clouds, presence of interfering sources, and ease of generation and detection. The transmitted ultraviolet light may contain both voice information and other data, impressed upon the light by frequency or pulse modulation using a Pockels cell light modulator. A corresponding receiver can be arranged as a transponder to determine range by phase angle differences between transmitted and reflected waveforms. By using an appropriate lens, the receiver can also determine the angle of incidence of a detected ultraviolet signal, and therefore the bearing of the transmitter.

Covert communication system using ultraviolet light

A sampling repeater includes a transmit/receive switch for inputting a received RF signal to a delay line. The delayed signal is then scrambled and fed to the transmit/receive switch, which changes its state so as to transmit the scrambled signal with minimal delay. A delay-stabilized oscillator is connected across the delay line and generates a control signal to produce a sampling waveform for the incoming RF signal. This waveform also synchronizes the transmit/receive switch so that the circuit becomes self-synchronized. The end result will be transmission of a scrambled incoming signal which will adversely affect the guidance of an incoming missile being guided with the RF signal simultaneously picked up by the repeater.

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Seacliff, NY, United States of America

Saulius Janusas