Deciphering Trunked Systems

Before you program a trunked system

To the average radio user, the complexity of a trunked system is invisible. Their radio is programmed up at the radio shop. They can still easily select who they need to communicate with by selecting a channel on their two-way. They can even directly call other radio users without tying up a dispatch channel — something they could never do before. As a scanner user, on the other hand, you need to know the different types of trunking systems in use, what options are available on each system, and three key pieces of information about any trunking system before you start any actual programming:

All of this information is usually available from the online database at RadioReference. The picture to the right shows a screenshot of a system from the database, with the pertinent information highlighted.
Sample system from the RadioReference database.

System Type

There are five major types of scannable systems; some of these also have subtypes. In the RadioReference database, you can generally determine the radio system type by looking at the line labeled System Type at the top of the screen (inside the red square in the screenshot).

P25 Systems

These are identified in the RadioReference database as Project 25 Standard . If the System Type line says anything else, then it is not a P25 system (even though it might have some P25 channels).

LTR Systems

These systems are identified as LTR Standard in the system type.

Motorola Systems

There are several subcategories of Motorola systems, but they will all have some form of Motorola in the system type: Motorola Fleetnet , Motorola Smartnet , Motorola Smartzone , etc. Once you have identified that it is a Motorola system, you can check the system frequencies to confirm its subtype:

EDACS Systems

There are three subtypes of EDACS systems:

Conventional Systems

This fifth type of scannable system is a general catchall for all non-trunked systems. See Conventional Systems for more information.

Non-scannable Systems

There are several system types that cannot be monitored with a scanner, either because the systems use proprietary digital formats that are not licensable by scanner manufacturers, or because the systems are not in wide enough use to make it cost-effective for manufacturers to develop a scanner that can monitor them.

These non-scannable systems are identified in the system type as:

System Voice

The other line inside the red square in the screenshot is System Voice , which summarizes the kinds of voice modulation used on the system. Youll find the following voice types:

Example of a mixed voice system.

The system voice also tells us when digital channels are mixed in with analog channels on the same system. Unfortunately, this means the system voice line can cause a lot of confusion. Just remember: system voice does not define the system type .

For example, in the system information shown to the left, we see that APCO-25 can be used as a voice type on a Motorola system that is not actually a P25 system . When we're trying to determine whether a system is a P25 system, we need to ignore the System Voice line and focus on the System Type line. If there is P25 Voice on a non-P25 system, the scanner can sort this out while scanning.

System Frequencies

The system frequencies section in the database lists all the frequencies used by the system (see the blue square in the screenshot above on the right). For Motorola and P25 systems, you will need to program only the system control channel frequencies: those are the frequencies shown in red (for primary control channels) and blue (for alternate control channels) in the database.

For EDACS and LTR systems, you will need to program all the listed frequencies and their associated LCN (that is a small number right next to the frequency). Some systems have multiple sets of frequencies. These are called multi-site systems: each set of frequencies corresponds to a different physical antenna site.

Talk Group IDs (Channels)

The Talk Group information section (inside the green rectangle) shows the different channels on the system and which agency uses them. You'll need to go through the list and make a note of the channels you want to hear. Then you can start thinking about how you want to organize those channels.

(Keep in mind that this screenshot shows just a few of the channels on a single system. One of the great features available to subscribers on RadioReference is the ability to tag channels directly on the site and print out a nicely-formatted hardcopy of each system. It makes this task much, much easier.)

This page applies to the following scanner(s): BCD996XT BCT15X BCD396XT BC346XT BC346XTC Users Guide

Topic attachments
I Attachment Action Size Date Who Comment
PNGpng RRmixedvoice.png manage 44.0 K 11 Dec 2008 - 20:10 UnknownUser  
PNGpng RRscreencallouts.png manage 228.6 K 11 Dec 2008 - 20:06 UnknownUser