Most repeaters have a "Courtesy Tone" (a short...beep or series of beeps) that will help in determining how long to pause. The courtesy tone serves two purposes. Repeaters have a time out function that will shut down the transmitter if the repeater is held on for a preset length of time (normally three or four minutes). This ensures that if someone's transmitter is stuck on for any reason, it won't hold the repeater's transmitter on indefinitely. (Don't laugh, many microphones get lodged in the fold of car seats and keep a repeater busy until it times out. Of course if it is not noticed soon by the mobile operator.....the control operator of the repeater may have to shut down the repeater until the problem is corrected.) When a ham is talking and releases the push-to-talk switch on their radio, the controller in the repeater detects the loss of carrier and resets the time-out timer. When the timer is reset, the repeater sends out the courtesy tone. If you wait until you hear this beep (normally a couple of seconds), before you respond, you can be sure that you are pausing a suitable length of time. After you hear the beep, the repeater's transmitter will stay on for a few more seconds before turning off. This is referred to as the "tail". The length of the tail will vary from repeater to repeater but the average is about 2 or 3 seconds.
You don't HAVE to wait for the "tail to drop" before keying up again, but make sure that you hear the courtesy tone (if used) before going ahead. Note: If you don't wait for the beep, the time-out timer may not reset. If you time-out the repeater, YOUR conversation AFTER the time-out will not be heard. The repeater time-out function does not care if you are still talking or not; and the station on the other end may rib you about hogging the machine and you will have wasted all those words! What is Doubling? When two stations try to talk at the same time on the same repeater, the signals mix in the repeater's receiver and results in a buzzing sound, squeal, distorted sound or severely jumbled and broken words.