Automatic mobile radio telephone system

Claim 1

A radio telephone system comprising an automatic radio relay station functioning as a repeater, a plurality of radio telephone stations incorporating transceivers for communicating among themselves by means of said radio relay station, said automatic radio relay station including a plurality of duplex radio channels each having a receiver and a transmitter operable respectively at a reception radio frequency and a transmission radio frequency, each radio telephone station transceiver including a receiver and a transmitter tunable to correspond to any duplex channel in said radio relay station, each called radio telephone transceiver including means to use the same transmitting carrier frequency and the same receiving carrier frequency as the corresponding calling radio telephone transceiver, the said transmitting and receiving frequencies being respectively identical with the receiving and transmitting frequencies of the relay-station channel which was available when the said calling radio telephone transceiver started its call, means enabling each channel in the relay station to be occupied by selective calls between two mobile stations, means causing an idle one of the channels in the relay station to transmit an availability signal to indicate the availability of that channel for calls, the availability signal including the channel transmission frequency modulated by a low frequency signal and transmitted at a power level reduced below the full power level, said radio telephone stations including means to cyclically scan the available channels by automatically switching pairs of frequencies, said radio telephone stations including means to stop the scanning in response to detection of the low frequency indicating an available channel, said radio telephone station including means by which it is enabled to transmit a relay triggering signal upon receipt of the availability signal, said relay triggering signal comprising a radio-frequency modulated with a low frequency which initiates the triggering of the relay station, means in the receiver of said relay station adapted to cause a switching de-vice to operate when said relay triggering signal is detected by the receiver in the unit that corresponds to the available channel, said switching device operating to turn the associated transmitter to its full power and to connect the outlet of said receiver to the modulation inlet of said transmitter and to transfer the low fre-quency modulation which features availability to another one of the non-occupied channels which last said channel then becomes the new available channel at the relay station, the receiver of said relay station including means to cause a switch-ing device to operate when said signal is received, said switching device turning the associated transmitter on to its full power and connecting the outlet of said receiver to the modulation inlet of said transmitter and transferring the low frequency modulation which indicates availability to another unoccupied channel, which last said channel then becomes the new available channel.