Abstract: A system for selectively obtaining information from a plurality of remotely located data indicating devices includes an interrogate source and a plurality of transponders each associated with a different one of the data indicating devices. The interrogate source transmits an interrogate signal for effecting the readout of a selected indicating device, the interrogate signal being a high frequency carrier amplitude modulated with a pair of low frequency signals to represent an eight bit sync code word, a four bit command word and a twenty-eight bit identification code word for addressing a selected transponder.

Abstract: The instrument uses a semiconductor gas sensor element energized with a regulated voltage source and placed in the atmosphere to be tested to generate a signal representative of the concentration of natural gas in the air. A meter displays the signal to determine whether the area is hazardous, and a variable repetition rate blocking oscillator feeding a speaker is responsive to the signal for generating an audible tick rate useful in locating a leak. The instrument is light-weight, portable, easy to use and intended to comply with industry standards as an intrinsically safe instrument.

Abstract: A frequency/space diversity data transmission system includes a transmitter for transmitting two or more distinct RF signals having the same modulation from different antennas separated a wavelength or more, the frequency spacing of the carrier signals being at least ten times greater than the frequency of the modulating signal, and a broad band receiver including a video diode detector and a frequency demodulator which recovers the modulating frequency from the carrier.

Abstract: A system for providing remote readout of a plurality of groups of data indicating devices including a control unit for each group of data indicating devices for receiving interrogate data signals transmitted over a communication line or RF signal link from an interrogate unit at a central location to the locations of the control units, and for transmitting the interrogate data to transponders associated with the indicating devices over existing electrical power lines to which the control unit and transponders are connected via existing electrical outlets. The transponders are responsive to the interrogate data to generate reply data representing the reading of an associated indicating device for transmission over the electrical power line to the control unit which effects the transmission of the reply data to the central location.

Abstract: A data transmission system for obtaining information from a plurality of data sources includes an interrogate source for transmitting RF interrogate signals to the locations of the data sources and a transponder associated with each data source for receiving the interrogate signals and for generating RF reply signals representing the information. The transponder includes a transmitter having a voltage controlled oscillator responsive to data signals at first and second levels to generate sinusoidal output signals at first and second frequencies, respectively, a wave shaping circuit which converts the output signals to sawtooth wave signals at the corresponding frequencies and an FM oscillator for providing a carrier signal which is modulated by the sawtooth signals to produce a broad spectrum of sideband signals of approximately equal amplitude.