Mobile radio with transmit command control

摘要

A mobile radio for operation in a system having a discontinuous transmission function, for example GSM, transmits silence descriptor (SID) frames when the transmitter is active (i.e. the PTT button has been depressed) but there is no voice input signal. The transmitter of a second mobile radio is initially suppressed but later enabled (80) when a respective receiver (50) detects SID frames on the radio channel when a transmit command is input (85). In this way the first radio user does not "hog" the channel. High and low priority mobile radios may be arranged to activate their respective transmitters according to different criteria when SID frames are detected.