Abstract: An apparatus and method are described for a radio frequency document control system that enables the location of documents, such as office files, to be automatically and rapidly identified. A host transceiver, controlled via a PC, transmits a coded RF signal, at a first frequency, to individually addressable, low cost, local exciters/transceivers located on shelves and/or in drawers. The local exciters, which may be sequentially addressed, retransmit the coded RF signal at a second frequency via an antenna. A passive radio frequency identification tag, containing the same code as that transmitted by the local exciter and attached to a document, such as a file folder, when in the vicinity of the antenna of the local exciter, is energized by the RF field and modulates the second frequency signal from the local exciter. The second frequency signal modulated by the energized tag is then directly received by the host transceiver.

Abstract: An electrically programmable security system includes a receiver responsive to particular radio frequency signals which include a predetermined digital code encoded on the radio frequency signal. The receiver generates a control signal upon detecting the presence of the encoded radio frequency signal. The receiver also includes a circuit for digitally communicating the predetermined digital code on a communication link. A transmitter includes a memory for storing a digital code and a circuit for generating a radio frequency signal at the radio frequency to which said receiver is responsive. The radio frequency signal generated by the transmitter is encoded with the digital code stored in the memory. The transmitter further includes a circuit for coupling with the communication link and a circuit for inputting the predetermined digital code from the receiver unit communicated on the communication link into the memory when the communication link is coupled to the coupling circuit.

Abstract: An improved miniature hand-held low power transmitter utilizing a surface acoustic wave (SAW) resonator as the control element to establish the carrier frequency of the oscillator. The SAW resonator stabilizes the frequency of the transmitter to within 0.05% of the center frequency of the SAW resonator for the condition of the user's hand enclosing the transmitter. This stability allows the companion receiver to operate at a narrow bandwidth, 0.1% of the center frequency of the SAW resonator, thus reducing the spurious noise received by the receiver. The configuration of the transmitter allows schemes such as pulse position or pulse width modulation to be utilized to encode the transmitted information. The physical size of the SAW resonator allows the transmitter to be mounted within a housing small enough to be enclosed by the user's hand.