Abstract: An inductive coupling interface couples a first electronic device to an inductive coupling link of a second electronic device. The second device link is in a coupling zone adjacent the interface. A separation plane separates the coupling zone from the interface. The interface includes a pair of coils arranged on one side of the separation plane opposite the coupling zone. The coils are coupled in series to receive an input signal from the first device and generate flux based thereon. Each coil is wound in a coil plane in a winding direction, and has a first flux face as defined by the winding direction and a coil plane axis residing within the coil plane. The first flux faces of the coils respectively face toward and away from the separation plane. The coil plane axes are parallel to one another and the separation plane, and the same distance from the separation plane. Each coil has inner and outer sides parallel to the coil plane axis and respectively closer to and farther from the other coil.

Abstract: A page party system for use in industrial environments, having a plurality of stations joined by a page line and by a single party line for providing multiple full-duplex conference calls over the single party line. Multiple full-duplex conferencing is achieved by combining single sideband suppressed carrier amplitude modulation and frequency division multiplexing.

Abstract: An intrinsically safe telephone as provided for use in hazardous areas. The telephone includes a single line instrument located in the hazardous area which, in turn, is coupled by a two-wire transmission path to a shunt diode barrier and a telephone line interface located in a safe environment. The telephone line interface reduces power of incoming ringing and audio signals. The telephone line interface further includes an off-hook indicating circuit which senses when the single line instrument is off-hook. The intrinsically safe telephone is useful in all hazardous environments as classified by the National Electrical Code and requires no explosion-proof housing.

Abstract: A loudspeaker having two horns defining two soundpaths passing therethrough an input for connection to a driver and an output for broadcasting an acoustic signal is shown to include a central channel connected at one end to the input, the soundpaths being coincident therethrough and a first transition member which defines separate channels for the soundpaths. Such separate channels serving to change the direction of the soundpaths. There is also shown a pair of side channels, the cross-section of the output ends of the side channels are defined by first and second dimensions, wherein the first dimension is larger than the second dimension. A pair of second transition members serve to again change the direction of the soundpaths. Such transition members have an output end defined by first and second dimensions wherein the second dimension is larger than the first dimension.

Abstract: An intrinsically safe telephone as provided for use in hazardous areas. The telephone includes a single line instrument located in the hazardous area which, in turn, is coupled by a two-wire transmission path to a shunt diode barrier and a telephone line interface located in a safe environment. The telephone line interface reduces power of incoming ringing and audio signals. The telephone line interface further includes an off hook indicating circuit which senses when the single line instrument is off hook. The telephone line interface further includes a bootstrap power supply for powering the single line instrument whenever the single line instrument is off hook. The intrinsically safe telephone is line powered and requires no auxiliary power in the hazardous environment. The intrinsically safe telephone is useful in all hazardous environments as classified by the National Electrical Code and requires no explosion-proof housing.

Abstract: This invention is an improvement of the intraplant communication system in U.S. Pat. No. 3,527,890. It comprises one base unit composed of a handset amplifier and speaker amplifier, each with its own integral power supply and each located on a common printed circuit board. This unit also features a disconnect device, formerly called a hook switch, which includes a radio frequency proximity detector which has no moving parts.

Abstract: This invention relates to a contemporary paging type telephone for use in coal mines, with an added dial feature to work in conjunction with a local telephone switchboard or central telephone office switchboard. It provides the features of a contemporary single channel paging telephone system with the additional advantages of:1. Multiple private line conversations2. Localized paging via dial system--calling party can name the person being called, avoiding confusion;3. All-station paging ability to locate roving personnel.The mine dial/page phone has a rotary dial adaptation and loudspeaker paging facility and is connected to an above-ground conventional telephone line by means of an interface device, also above ground. The interface, one for each line, renders the telephone dialing system permissible for use in coal mines. The interface also provides, automatically, the emergency function required to support communications should there be a failure of telephone switchboard or central office service.