Oct 1, 2008 12:00 PM, By Mark Vitosh

Interoperable communications can be made easier through the use of frequencies set aside by the FCC

These additional radios ensure that the interoperability solution is capable of communicating with other radio users operating on a frequency from the pool. Using the virtual-talk-group capability and patching one or more of the pool radios with an agency's standard jurisdiction frequencies/talk groups gives visiting agencies the ability to communicate with jurisdictional radio users without actually having to reprogram radios.

This approach has an added benefit to the host agency. While reprogramming or swapping radios can make them difficult to control once they are deployed, the host agency remains in full control of a virtual talk group by maintaining the ability to activate or deactivate it as needed.

For example, let's say your local jurisdictional radio system is a Project 25 (P25)-compliant trunk radio system operating in the 800 MHz band, and you have an assigned talk group on that system that your radio users tune to for incident command. When a large-scale incident occurs, your local authorities request mutual-aid assistance.

A fire department from a neighboring state agrees to send a pumper truck and a five-person crew for two weeks to assist. When the pumper truck arrives and is briefed at the emergency operations center (EOC), it is discovered that the pumper truck and crew have VHF radios that have been preprogrammed with the VHF TAC set of frequencies from the interoperability pool as part of their jurisdiction's radio frequency plan.

Having deployed an interoperability solution with the capabilities shown in the diagram, including a set of radios capable of operating on each of the public-safety pool bands, the EOC had created a virtual talk group that includes the local 800 MHz trunked radio talk group for incident command, V-TAC 1, U-TAC 1D, and I-TAC 1D.

By adding the local P25 radio tuned to the incident talk group and each of the interoperability pool radios into a virtual talk group, the pumper truck and the crew's portable VHF radios can communicate with the incident-command talk group on the P25 800 MHz radio system by simply setting their radios to V-TAC 1.

With both parties having this capability to use the FCC interoperability frequency pool, the pumper truck and five-person crew can use their existing radios during the mutual-aid assignment and communicate with incident command on the P25 800 MHz trunk system. Without this capability, the local jurisdiction may have had to assign up to six P25 800 MHz radios to the truck and crew.

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