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First things first - please read and understand my file Radio Repeaters - A Simple Explaination
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Continuing -
Trunked radio systems use multiple repeaters. If Car 1 wants to talk to Car 2, the computer system switches the radios in Car 1 and Car 2 to the correct frequencies in order to use a repeater that is "open for business"/"free"/"available"/"not in use at the moment". Trunked radio systems typically have 5 or 10 or 20 repeaters at each hilltop site.
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July 20, 1998 - Additional Info - Here are a few definitions and concepts to help you grasp the big, brave, new world of trunked radio systems.
Control channel - this is the "home" channel for your radio - this is the channel that your radio tunes/hops/switches to when you turn it on - on this channel your radio hears a stream of data from the computer which runs the TRS - your radio receives its marching orders on this channel - if the computer wants your radio to switch to Channel 68 to talk to some other unit, this is the channel where the "switch channel" command will come down from the hilltop to your radio.
Talk group - like a "channel" of the older radio systems - instead of saying that all police cars in your town talk on Police Channel 1, a trunked radio system will say that all Police Units are to operate on "Talk Group 1" - its almost the same thing but just a little different - actually the technical aspects are a lot different but from the users point of view - it is pretty much all the same stuff.
Conventional channel - a non trunked radio channel - the type of radio channels you used to have before you moved up into the brave new world of trunked radio systems.
Failsafe channel - when the big computer on the hill dies/fails/craps out, then all field unit's radios automatically switch over to "converntional" operation on a "Conventional" channel - of course if the converntional channel uses a repeater, and this conventional repeater is dead, then you are up the creek. If the failsafe channel is a simplex channel (non-repeaterized in other words), then you can expect your radio range to be about 2 shoestrings and a half long. Well, maybe not quite that bad - but dont expect a lot!)
(I really hope that this additional info has not added more confusion to your sunny day).
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May 10, 1999 - Update - try this site for a little technical info on one type of trunked radio system - �LTR Site�
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3 April 2000 - Update - Trunking Info on the www.genesisworld.com website
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Update - 20 Dec 00 - a few minor changes to layout - no changes to text