What is trunking?

Traditional radio equipment works because all parties involved in the communication agree on what frequencies they will utilize. Traditional radio scanners work by scanning for and then listening to those frequencies.

Trunking radios, on the other hand, constantly renegotiate the frequencies utilized for the conversation. This allows for more efficient utilization of limited frequencies because each conversation does not require a dedicated channel. However, it also makes it very difficult to scan trunked conversations because you do not usually know what frequency the next portion of the conversation will appear on.

Trunked radio systems are utilize one or more "Control" or "Data" channels. The data passed via the control channel instructs each radio in the system which frequency to switch to in order to remain on the selected channel. Several utilities are available to monitor and decode some of the common trunking protocols: