<Li> Disadvantage: If a radio cannot reach the repeater, it cannot communicate . </Li> <P> Some systems use a mix of the two where radios use duplex as a default but can communicate simplex on the base station channel if out - of - range . In the US, the capability to talk simplex on a duplex channel with a repeater is sometimes called talk - around, direct, or car - to - car . </P> <P> In two - way radios with headsets, a push - to - talk button may be included on a cord or wireless electronics box clipped to the user's clothing . In fire trucks or an ambulance a button may be present where the corded headset plugs into the radio wiring . Aircraft typically have corded headsets and a separate push - to - talk button on the control yoke or control stick . Dispatch consoles often have a hand - operated push - to - talk buttons along with a foot switch or pedal . If the dispatcher's hands are on a computer keyboard, the user can step on the foot pedal to transmit . Some systems have muting so the dispatcher can be on a telephone call and the caller cannot hear what is said over the radio . Their headset microphone will mute if they transmit . This relieves the dispatcher of explaining every radio message to a caller . </P> <P> In some circumstances, voice - operated transmit (VOX) is used in place of a push - to - talk button . Possible uses are handicapped users who cannot push a button, amateur radio operators, firefighters, crane operators, or others performing critical tasks where hands must be free but communication is still necessary . </P>

What is the function of the ptt button on a two-way radio