GB1384392A - Speech communication systems - Google Patents

Abstract

1384392 Intercommunication systems PLESSEY CO Ltd 13 Dec 1972 [15 Dec 1971] 58171/71 Heading H4K A speech communication system suitable for use in a deflagable atmosphere comprises a plurality of separately powered networks each comprising a plurality of loudspeaking telephone stations connected to a common communication cable, each station including a press to speak switch which when operated enables the other stations connected thereto, the networks being interconnected by speech detector/coupling units which in response to detection of speech in any one network enable all stations of every other network to allow simultaneous reception of speech thereat. The networks may be connected in series, in series parallel or in parallel. In one embodiment detailed the system also includes a separately powered coupler unit arranged to communicate with an operators position by tone signalling. The operators position which is at the pit head may provide connection to the public telephone network. Each station also includes a signalling switch for D.C. loop signalling to the operator, the signal being repeated in each coupling unit by relays as far as the separately powered coupler unit and thence transmitted in tone form to the surface, tones and speech from the operator enabling all stations of the system.