Portable radio telephone

Abstract

A system for radio-telephone communication between a user at a remote location and the commercial telephone system or between two users at remote locations comprises a fixed terminal that is connected by wire lines or the like to the commercial telephone system and a plurality of portable radio units. The terminal is equipped for duplex operation on a plurality of channels, each of which uses separate frequency bands for transmitting and receiving. Each of the portable units is a simplex transceiver adapted to receive on each of the frequencies of transmission from the terminal and to broadcast on each of the frequencies received by the terminal. The terminal places a channel acquisition tone on an unused channel that is the next to be used. The terminal calls portable unit by shifting channel acquisition tone to another channel and broadcasting an identifier to the portable unit. The called portable unit responds to its individual identifier by sounding an audible alert and producing an audible verbal message if one is sent from the terminal. A portable can also originate a message by calling the terminal. A delay period provides time for the portable to recognize its identifier before beginning to scan for channel acquisition tone. Circuits and logic in the portable produce a busy signal if the user attempts to call at a time when the portable is not receiving channel acquisition tone. A reset in the portable unit provides means for the user to terminate the call.