Abstract: In a press-to-talk system of radio telephone communication, the operator's particular voice signal actuates a switching signal generator to generate a transmit-receive circuit changing signal which connects the circuit of the radio telephone equipment for transmission or for standby. A characteristic tone signal is also generated for each switching changeover of the radio equipment to inform the operator of the switching changeover of the equipment. The press-to-talk manual switch and the pilot lamp for indicating the state of the circuit connection are eliminated, and the operator can use his hands and eyes for other operations while he is using his radio telephone equipment. A feature of the invention is the use of two different frequency tones to indicate equipment mode or logic status by indicating the direction of logic-state change.

Abstract: In a press-to-talk system of radio telephone communication, the operator's voice signal actuates a switching signal generator to generate a transmit-receive circuit changing signal which connects the circuit of the radio telephone equipment for transmission or for standby. The audio-frequency signal from the output of the receiver of the radio telephone equipment is properly isolated from the input to the switching signal generator.In this way, the press-to-talk manual switch is successfully eliminated and the operator can use his hands for other works while he is performing the radio telephone communication. This elimination of the press-to-talk manual switch is advantageous for a radio telephone operator when he is driving a car, working at a construction or a quarrying site, or when he is engaged in a fire extinguishing operation.