Abstract: A personal identification instrument is comprised of a substrate, and carried on the substrate: a photograph and/or a personal signature, personal information relating to the legitimate holder of the instrument, and an encrypted machine readable security code carried by the instrument, the code being comprised of a combination of digitized personal information and a digitized descriptor of the photograph and/or personal signature.

Abstract: A first terminal for use in a time division duplex communication system comprising apparatus for automatically, successively, repetitively and alternatingly transmitting and receiving compressed signals to and from another terminal via a single transmit and receive time divided channel, including apparatus for changing a transmit and receive mode of the first terminal in synchronism with an opposite transmit and receive mode of another terminal, apparatus for receiving a timing signal which is the same timing signal received by another terminal, and apparatus for changing the mode at intervals determined from reception of the timing signal.

Abstract: A MODEM for a high frequency radio data link which substantially enhances the recovery of data transmitted via the link in the face of multipath distortion and fading. A serial digital input signal for transmission is split into odd bit and even bit data streams, having synchronous bit timing. Each pair of bits, referred to as a symbol, is phase shifted by .pi./4 which encodes its timing, for later clock recovery. The resulting signal is then twice differentially phase encoded which facilitates the recovery, when demodulated, of the original symbols overcoming the effect of Doppler shift and/or transmitted oscillator center frequency offset. The resulting signal then phase modulates a subcarrier signal having a frequency much higher than the symbol rate, and the phase modulated subcarrier is converted to a spread spectrum signal for transmission. This digital signal is provided to a high frequency analog transmitter for transmission with the signal spread over a particular HF channel, to a receive point.

Abstract: The voice processing system for radio telephone consists of a compressor in the transmitter and an expander in the receiver. The compressor divides the input voice signal into syllabic groups and applies a gain to each syllabic group depending on the peak amplitude of the signal of the respective group, resulting in a reduction or compression of the dynamic range of the voice. The expander on the other hand increases or expands the dynamic range of the signal restoring the voice to its original form. The compressor and expander are synchronized such that the amount of expansion or instantaneous gain in the receiver is exactly the reciprocal of the amount of compression in the transmitter, i.e. when the gain of the compressor is N, the gain of the expander is 1/N. In this way the total system gain is always unity and is therefore transparent to voice and other analog signals passing through it.