They would get a beep-beep when they tried to key up (busy signal). Trunking is based on mathematical models of radio user behavior. As an example, for small groups of radio users you can apply a 5-5-90 rule: Any particular radio user transmits 5% of the time, receives 5% of the time, and is idle 90% of the time. In a one-freq per group scenario, you are wasting 90% of your radio frequency asset. Of course for major metro dispatch channels, their ratios are higher, but still not at 100%. Trunking is a way to maximize the benefits of your radio frequency assets.
In a well-designed trunked system, busy signals are fairly rare. In the event of a widespread disaster, certain users are given a higher priority on the system, so they can essentially "kick off" other users of lower priority.
By the way, this system has been used for phone systems for many decades. While our building has 300-400 extensions, we probably only have 20 incoming lines. That works because it is very rare for more than 20 people to be involved in an outside phone call at any one time. (Our call center is on a seperate system where the ration of extensions to trunked lines is closer to 1:1.) The same hold true for every "exchange" in the phone network. There are many more local lines coming into an exchange than there are trunked lines going out.
Last edited by UPMan; 07-30-2009 at 12:02 PM..
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