Agenda Packets - 2012/08/13 - Laserfiche WebLink

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Appendix D D-2 Ramsey County Multijurisdictional Hazard Mitigation Plan | July 2012 State Radio Board (SRB) oversees the system. Counties are responsible for system portions they built, but must operate within SRB rules. The Ramsey County 800 MHz radio system is a portion of the Minnesota ARMER trunked digital radio system. Because of the connection to the state system, Ramsey County radios can communicate with any other 800 MHz radio anywhere in the State with radio coverage. The Ramsey County radio system uses APCO Project 25 digital modulation. This robust modulation scheme works well beyond the boundaries where older FM radio systems fail. This means that the radio transmissions stay clear and easy to understand inside the network. The Ramsey County portion of the ARMER system consists of seven radio sites around the County, each with 22 transmitters. The radio sites are connected by microwave transmissions and fiber optic cable. One transmitter, used as the "control channel," directs the system-affiliated portable and mobile radios where they should go to send or receive their transmissions. The other 21 transmitters are used as required to transmit the more than 350 virtual channels ("talkgroups") programmed into various Ramsey County radios. The transmissions of other talkgroups that originate in Ramsey County, other counties, or at the state level are sorted by the control channel that respond to what each radio is tuned too. The 22 transmitters employed by this system do the work of many old style transmitters. Since the system's portions interconnect, each site transmits the same transmission, providing protective redundancy against the failure of one or more sites taking the entire system off the air. Even if the whole Ramsey County system were to fail, the radios would automatically affiliate with one of the other county or the State sites and transmissions would continue with minimal interruption.