Western North Carolina Scanner Club
Scanning WNC Since 1999
Trunking
When you say Trunking You have said a mouth full !
( The simple Defination )
Trunking a just another way of communicating using a two way radio system on the same frequency without stepping on anyone else who may be using it as well.
Now lets get into it a little deeper
Trunking is a way of using a set of frequencies in a more efficient manner than the old conventional way ( Analog ) . In the past, each agency in an area had frequencies licensed to them by the FCC. They would then would use those discrete frequencies just for themselves. Since there is a finite amount of available radio spectrum as the number of users increased crowding and interference has occurred.
Trunking is the use of several repeaters, on different frequencies in the same band, operating together under computer control to allow the pooling of resources for several agencies.The trunking transceiver is a frequency agile radio capable of receiving instructions and changing frequencies on the fly. All trunked radios operate in a similar manner although the type of trunking technology used by each type of trunked radio system differs greatly.
In the trunked radio environment, each agency is assigned one or more talkgroups that the agency's communications will use. All agencies on the system will have different talkgroups but all will share the same pool of frequencies. For simplicity I will use an example of a control channel-based type of trunked radio system as an example. In this type of system, all the radios on the system (except the computer controlled set of repeaters, of course) listen to a common control channel (CC) output frequency and transmit (initially) on a common control channel input frequency, unless they are listening to a conversation on a talkgroup.
How the system work is this. Unit 23 wants to tell the dispatcher that he is now in service. The following actions take place in a very short time, much shorter than it takes you to read this. He picks up his microphone and keys the mike, his radio sends a signal on the CC input frequency, which the controlling computer understands as a request for a channel grant for the talkgroup assigned to Smalltown Police, his radio then instantly goes back into receive mode. The computer looks at the system for an empty channel pair and issues that channel grant on a specific channel pair and sends that channel grant information out on the CC output channel. This channel grant information tells all radios on the system, if you are listening (monitoring) for communications on the Units talkgroup: change to channel pair XX on the system for a communication. All radios tuned to Smalltown Police's talkgroup, including Unit 23, then switch frequencies to that channel pair granted by the computer.Unit 23's radio, after changing frequencies, goes into transmit mode and he can start to talk. As he talks, all the radios monitoring the Units talkgroup are now listening on the assigned repeater output channel and are ready to talk on the assigned repeater input channel. This continues until Unit 23 has finished his transmission. On some types of systems, further communication may be on the initially assigned channel pair or it may move to another, but the process stays the same.
A trunking system that uses more than one site is either a multi-cast (sometimes referred to as simulcast) system covering a larger but restricted area, like a mid-sized city; or a networked system. A multi-cast system could also be part of a larger networked system.
Networked systems typically are made up of a trunked system that uses control channels as opposed to a LTR type system. The reason this is important to you the scanner user is that you must accommodate the use of multiple control channels in your scanner programming. For the purposes of this discussion on networking, we will only consider those systems that use control channels to manage usage (as described in the above section.) Also, in networked systems that also have multi-cast systems, consider the multi-cast system as a single site within the network.
Trunking Scanners
A trunk-tracking scanner is designed to follow those same instructions (except, of course, it ignores the instructions relative to the input side of the repeater pair) so that it will also follow the conversations by changing frequency to the appropriate repeater output frequency. Each type of trunked radio system operates a little differently, and some cannot be monitored by current trunk-tracking scanners at all.
Please take a look at detail information in regard to the type of system that you are attempting to monitor and the instructions that come with your scanner in regard to that type of system.
TrunkTracking (FAQ'S)
FAQS
What is TrunkTracking or a TrunkTracker?
A TrunkTracker is a scanner that is capable of tracking analog trunked two-way radio systems used by police, fire, EMS, and other two way radio. For an explanation of trunking please scroll back to the top of the page
Where can I buy one and how much does it costs?
Most trunking scanners vary in price! You can find a used one on Ebay (www.ebay.com) also by looking in your local classifieds section for under $100. You can watch the WNC Scanner Club Classified for a unit that may come available . Also the scanning news groups or mailing lists to get a better idea of going rates and availability for a used unit.
New Units can be bought at your local electronics dealers like Radio Shack. Or online at
Do I need one?
If you want to monitor Motorola I , II or III as well as , EDACS, or LTR trunked radio systems, YES! Although you can scan the analog trunked systems with a conventional analog scanner, a TrunkTracker really makes scanning trunked systems more enjoyable. The larger the number of users on a trunked system, the more you need a TrunkTracker. With a TrunkTracker you will be able to monitor a channel or "talkgroup" without having to continue to hit the scan button like you would have to do with a conventional scanner, AND you can lockout data channels and public works channels that would otherwise be a real pain.
Who makes TrunkTracing Scanngers?
Do you need to know all of the frequencies of the trunked system you want to monitor?
Yes, in most cases. Even though the frequencies may be part of the data stream that the TrunkTracker monitors it is still necessary to program in all of the frequencies used by the trunked system. The newer generations have "Control Channel" and Software Programable usig your PC or Mac .
Does a TrunkTracker work like a conventional scanner?
Yes. You can either scan conventionally or TrunkTrack.
Can you scan conventionally and TrunkTrack at the same time?
YES
Can you TrunkTrack more than one trunked system at a time?
YES
How may types of trunking are there?
- Type I
- Type II
- Type IIi Hybrid
- Type II SmartZone
- Type II SmartZone OmniLink
- iDEN (integrated Digital Enhanced Network)
It sounds really complicated, is it worth the trouble?
Yes!
Tips
When TrunkTracking, think of talk group ids as frequencies. You have to figure them out just like you had to figure out what frequencies to listen to. You can search for them, you can scan them, you can manually tune them. There can be hundreds of them on a trunked system.
The same talk group id can be used in separate trunked systems and may have absolutely no connection between the two.
If you hear users talking about going to another channel and you don't know what that channel is, hit SEARCH! For example, you are monitoring talk group id 2160 and you hear one officer transmit to another "321 to 329, go to talk one". Hit the search key and listen for the same voices or a response like "329 to 321, on talk one". Log that talk group id with the note Talk 1.
In a Type I block, primary users' primary channels are likely to be on ###-1 For example, you are more likely to see Police on 700-1 and Animal Control on 700-15, than Animal Control on 700-1 and Police on 700-15. However, this is only a rule of thumb, and there's reason it couldn't be the second way.
Use a spreadsheet or other program to help sort out and organize the talkgroup and fleet information you find.