Understanding Trunking Systems

One of the biggest advantages of the new digital scanners is the ability to follow a Trunking system or "Trunk-Track". 

I'm sure you are thinking "What does Trunking even mean?"

With the advancement of radio technology digital radio systems have gone to a system referred to as a Trunked Radio System. A trunked system is a complex computer-controlled two-way radio system that allows users to "share" a set of frequencies. Instead of selecting a specific frequency for a transmission, the radio selects a programmed trunking bank in the system. The trunking system then transmits on the first available frequency and sends (on a different frequency called a control channel) a code that identifies that transmission. That code is a TalkGroup ID (or sometimes referred to as just ID)

The main purpose of this type of system is efficiency since many people can carry many conversations over only a few different frequencies. Trunking systems are popular amongst government entities as they allow fire, police and other municipal services to share a system allocated to a city, county or other entity. 

So what does that mean to me?

Well the basic answer is you are not going to be scanning a frequency but rather a TalkGroup ID. Since a trunking system might send its call and response on different frequencies, a "Trunking" or "Trunk-tracking" scanner is needed. These scanners will let you monitor the control channel frequency as part of the TalkGroup so you can hear both calls and responses and more easily follow conversations.

The following systems use trunking: 

  • DMR - Digital Mobile Radio
  • MotoTRBO Capacity Plus (Motorola)
  • MotoTRBO Connect Plus (Motorola)
  • Motorola Type I 
  • Motorola Type II 
  • Motorola Type IIi Hybrid 
  • Motorola Type II Smartnet 
  • Motorola Type II Smartzone 
  • Motorola Type II Smartzone Omnilink Motorola Type II VOC
  • P25 Standard
  • P25 X2-TDMA
  • P25 Phase I and Phase II
  • EDACS Standard (Wide) 
  • EDACS Narrowband (Narrow) 
  • EDACS Networked (Wide/Narrow) 
  • LTR Standard

Each type of system uses their control channels slightly different. For more information about each system type visit this page on Radio Reference.