Trunk Tracking Scanners and how they work
using Motorola's method of trunking.
Years of scanning the airwaves with regular scanners are quickly becoming the thing of the past. Most cities are now going to trunked systems to increase the quality and preservation frequencies. The old way: Transmitions on the old system was typically on 'one' frequency. For example, the Sheriff Deparment would always be on 460.1000 and the city police would always be on 460.2000. You would program those frequencies into your scanner and keep up with all traffic they were responding to. With the old system, each and every service the city and county had its own frequency. That would mean lots of money to pay for equipment and frequencies issued to a single county. You could have virtualy hundreds of frequencies you could monitor in our county alone. The new way: Trunk systems offer many advantages to a city and county. First off, you can put most, if not all, of the county and city services on the one system. You can do this with as little as 5 frequencies and up to about 30 frequencies depending on the size of your county and cities using it. How can they do that you ask? Here is the reason, THEY ALL ARE NEVER TRANSMITTING AT THE SAME TIME!!! Trunk systems have a group of frequencies called 'Control Channels'. These channels control the system by assigning a transmited signal to a 'voice channel' in the system. Each and every time a transmited signal is detected by the 'control channel' it looks at a unique ID that the signal contains. This ID is assigned to a specific group of users such as a police department for example. Every radio in the police department have the same unique ID number in every radio the have from their Handhelds, their car radios, and even the dispatcher. Once the 'control channel' identifies the ID number, it transmits this ID and every radio that has this ID will recognize that the Trunk system is going to transmit a signal that they need to hear. Then the system tells all radios with that ID what 'voice channel' it is assigning the tranmited signal and ALL radios with that ID will switch to that channel to receive it. When the signal stop transmitting ALL radios start listening to the 'control channel' again for another transmition. When this happens the process repeates itself, except the 'voice channel' might be a different one this time. Then they ALL switch to that channel. Example: Dispatcher: "1 Adam 12" Voice channel: 856.2375 1 Adam 12: "Go ahead" Voice channel: 860.2125 Dispatcher: "10-20" Voice channel: 858.6125 1 Adam 12: "Burger King" Voice channel: 859.8375 Dispatcher: "10-4" Voice channel: 857.6375 That is why it is quite difficult to follow a police department that is using a Trunk system, the 'voice channel' is always changing. If you have a scanner that is 'Trunk Tracking' capable, you can store the 'control channels' in memory and program the scanner with the unique ID and the scanner will be able to follow the siganls that you want to monitor to the 'voice channel'. If your counties Trunk system has many users and can handle up to 30 transmited signals at the same time, you can have 30 active 'voice channels' at once. But since it is nearly improbable that this happens simultaniouly, this is why you can put hundreds on users on the SAME system. Each user will have its own unique ID and ONLY those with that ID will follow the transmited signals. This being the case the Police department will never hear the Fire department or any other county service, except on designated ID's that allow Dispatchers to talk to each other. Getting started with Trunk Tracking scanner can be a little confusing at first. Mainly because you have to change the way you scan frequencies, but once you get the hang of how the system operates, it will be just like the old days. It took me about 1 week to get familiar with how trunking worked and to get my scanner programmed correctly. Now I can enjoy both the old and new ways scanners work. You can find many listings on the internet and even a few here on my webpage that give you the unique ID's used for each county service that uses Trunk systems. The frequencies shown will be control channels and the ID's will designate the service using it. If your scanner is capable of doing "Control Channel Only" mode, you ONLY have to program 'Control channels' into your scanner. The system will tell your scanner where the 'voice channel' is and your scanner will switch there on its own. If your scanner isn't capable of "Control Channel Only", then you have to enter in ALL the frequencies of the trunk system. There are few different types of trunk systems in use today, this explaination was for Motorola. EDACS and Johnson LTR are others, but since I don't have any EDACS system or Johnson LTR systems to monitor around my area, I can't give any information on them. There are many website that contain information for these system on the internet in case you do need to know how to monitor them. I hope this helps you understand how a Motorola system works, and how your scanner will track it. Most systems in use today use this system. It is reliable and much information is available for it.
Take care and Happy Scanning.... N4YEK