Abstract: A cashless business transaction system (e.g., a vending system, a material tracking system, or a highway toll system) incorporates a method and apparatus for transmitting a digital information signal. A signal generator (311) generates a constant frequency signal. A phase modulator (305) varies the instantaneous phase of the constant frequency signal to represent digital information, thereby producing a phase modulated signal (325). A tuned resonant circuit (307) filters and averages the phase modulated signal to produce a simulated FM signal, and transmits the simulated FM signal via its antenna (309). One such business transaction system (e.g., a vending system) incorporates such a transmitter to facilitate transmission of billing information from a device located within a substantially electrically shielded environment.

Abstract: An RF signaling system and system for controlling the whereabouts of animals utilizing same functions, in a preferred embodiment, by efficiently establishing well-defined electronic boundaries using small, battery powered transmitters transmitting constant envelope RF signals in a near-field regime by repetitively delivering trains of brief, low duty cycle pulses of electrical energy to a resonant circuit which includes an antenna at a low RF carrier frequency corresponding to the resonant frequency of the circuit. During intervals between pulses, the resonant circuit is effectively isolated from the circuit delivering the pulses to minimize loading effects. Further energy efficiency is achieved by interposing inactive interals between at least some successive transmissions of the RF signals represented by the pulse trains. The RF signals emitted by the transmitters are digitally encoded as are those emitted from a wire loop coupled to an optional wire loop unit to define a wire loop boundary.

Abstract: A transmitter prepares digits for transmission, e.g. as spread spectrum data accompanying commercial radio, using code sequences having exactly zero cross-correlation. The code sequences include phased versions of the maximal length sequence, with an additional "0" bit appended to the end of each phased version. Information signals (which may be analog signals, or digital signals encoded as two or more analog levels) are transmitted by multiplying each information signal by one of the code sequences, and adding the resulting sequences together to form an output sequence for transmission. A receiver that recovers the information signals correlates the received sequence with each of the code sequences, producing results which are directly proportional to the information signals.

Abstract: The whereabouts of a pet or other animal are controlled using one or more transponders to established a boundary. The transponders receive an incident signal from a transmitter and generate a distinguishable return signal which, when the animal moves into proximity of the boundary, is received by a unit affixed to the animal to initiate application of an aversive stimulus which deters the animal from traversing the boundary. The transponders can be active or passive and can be located to establish either fixed or mobile boundaries.