PURPOSE: To select one set of public telephone set for a mobile telephone system or a radio telephone system by using a signal conversion section to convert a state change of a 2-wire line current into a digital control signal.
CONSTITUTION: When a public telephone set 14 makes dialing while a train is running on a trunk line, a telephone number of a talking destination terminal equipment is sent to a telephone station via a train telephone ground station. The telephone station stores a number of the telephone set 14 to call the talking destination terminal equipment and a speech line is formed via a train ground station between the telephone set 14 and a telephone terminal. When the train enters a branch line in this state, a switching signal (c) is sent from a line changeover control section 23 and the telephone set 14 is switched to the position of a digital transmitter-receiver 20. An analog receiver 13 detects the switching operation to send switching information to the telephone station via the train telephone ground station. Upon the receipt of the call, the telephone station calls the telephone set 14 via a radio ground station by a telephone number of the telephone set 14 stored and switches the speech channel of the talking destination terminal equipment to the radio telephone ground station from the train telephone ground station.
ARAMA SEISHI
YAJIMA TSUNEO
HOSHI SATOSHI
NIPPON TELEGRAPH & TELEPHONE
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