Conventional scanning is a simple concept. You enter a radio frequency in your scanner's memory which is used by someone you want to monitor. For example Police, Fire or Highway Dept. So when your scanner stops on a frequency, you usually know who it is , and more importantly, you can stop on a channel and listen to a entire conversation.

As the demand for public communications has increased, many public radio users don't have enough frequencies to meet their needs, and this has created a serious problem. Trunking radio systems solve this problem by allowing various groups to use the same set of frequencies. For instance, the Police could share with the Fire Dept. or the Parks Dept. could share with Public Works, and so on.

In a trunked radio system, which contains 3 to 29 different frequencies, radio users are divided into groups, often called talk groups, and these talk groups are assigned specific IDs. When someone in a talk group uses their radio, a brief burst of data is broadcast before each transmission. The trunking system computer uses this data to temporarily assign each radio in a talk group to an available frequency. If the group using a frequency stops broadcasting or pauses between replies for a few seconds, they are removed from the frequency so another talk group can use it.

Sharing of the available public service frequencies, or trunking, allows cities, counties, or other agencies to accommodate hundreds of users with relatively few frequencies. On the other hand following a conversation on a trunked system is difficult, if not impossible, because  when there's a short break during the conversation you're monitoring, it's possible that the talk group will be assigned to a completely different frequency in the trunked system. This type of scanning is difficult and frustrating.

That's where the trunk tracking scanners come to the rescue. They will read the data burst and follow right along just as if you were part of the talk group your listening to. All you do is enter the frequencies that make up the particular trunked system and enter the talk group code, the scanner will do the rest, and you wont miss a thing.