12 Basic OperationTransmit TimerYour radio may have a transmit timer that limits theamount of time you can transmit continuously. When thetransmit timer is about to expire, the red LED flashes andthe radio gives three beeps. You must release the PTTbefore you can transmit again.Note: Your radio may be unable to transmit fora short time after the transmit timer hasexpired.Receiving aCallWhen there is valid activity on your radio’s currentlyselected channel or group, the radio then unmutes andyou can hear the call.If the incoming call contains special signalling thatmatches the signalling programmed for your radio, thegreen LED flashes and your radio may give a ringing tone.What YouHear on aChannelYour radio may be programmed so that you hear allconversations on a channel, or your user group may besegregated from other user groups by using specialsignalling. The special signalling is used to control themuting and unmuting of your radio, so that your radio ismuted when other user groups are talking and unmutedfor members of your user group.There are two muting controls that operate in your radio: signalling mute, and squelch.Signalling MuteThe radio’s signalling mute only allows the radio tounmute if the incoming call carries the tones specific toyour user group. Your user group may use tones that areeither audible, subaudible or both.