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Mining Publication: A Multiplexed Phone System for Small Mines

NOTE: This page is archived for historical purposes and is no longer being maintained or updated. Contact NIOSH Mining if you need an accessible version.

Original creation date: July 1982

Image of publication A Multiplexed Phone System for Small Mines

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.

Authors: JR Means, G Bowser

Conference Paper - July 1982

NIOSHTIC2 Number: 20031849

The Sixth WVU Conference on Coal Mine Electrotechnology, Cooley-WL, ed., Morgantown West Virginia, Jul 28-30, 1982, 1982 Nov; :116-123