What is a trunking radio system?
First, you must understand what a conventional radio system is. There are several types of conventional radio communications. One is “simplex.” That is where units use one frequency to talk to each other. For this example we’ll use the tactical frequency for the Chisago County Sheriff’s Department (153.860). One unit will transmit on that frequency and another unit will be able to hear on that frequency. Simplex frequencies are limited by transmit power and line-of-sight. Then there is a repeated radio system, or “duplex.” Again, we’ll use Chisago County for this example. On a duplex system, a unit will transmit on one frequency referred to as the “input” frequency (155.910). That signal will be broadcast from the squad car into the repeater or tower. Then, the repeater takes that signal, amplifies it, and re-broadcasts it (immediately) on another frequency, referred to as the “output” frequency (155.310). The output frequency is the frequency that you would normally put into your scan
