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Radio Communi Ions In Coal Mining

Abstract a communication system for underground mines which utilizes radio frequency waves at a first carrier frequency f1 within the range of 300 khz to 3 mhz carried along a conductor which extends from the exterior of the mine into the mine and communicates with a plurality of mobile transceivers receiving on the frequency f1 and transmitting on a different frequency f2 at least 60 khz.

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