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A Multiplexed Phone System For Small Mines
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1982
Source: Proceedings of the Sixth WVU Conference on Coal Mine Electrotechnology, Morgantown, West Virginia, July 28-30, 1982. Cooley WL, ed., Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, Contract J0123017, 1982 Nov; :116-123
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Description:A new phone system was developed that provides eight full duplex communications channels over a single twisted shielded phone line, with no central switching station or line amplifiers. This system greatly simplifies installation and maintenance over that required with conventional switching systems. The system is based on microprocessor technology and digital frequency synthesis. Frequency division multiplexing is used over a bandwidth of approximately 300 kHz, and a baseband voice channel (compatible with conventional pager phones) is provided as a backup to assure communication if the multiplex features fail. Multiplex operations are controlled over a 30-kHz digital channel. The system is designed to operate with up to 16 km (10 miles) of cable plant and a maximum phone separation of 8 km (5 miles). The digital techniques permit a limited amount of monitoring and control capability to each phone. This consists of two pair of contact inputs or outputs, to be used as desired. These "flags" may be read or controlled by a dispatcher's phone.
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