Primarly use MSP 800 mhz trunked system. Initially on launch they will notified station G on the STATEWIDE talkgroup. When they fly into a particular troop area they will contact the troop on the appropriate troop working talkgroup. MSP helos also have capability to contact any non digital local, county, or area law enforcement activity. Many times they will talk on the repeater output frequency direct rather than using the input. Callsign on law enforcement frequencies will be AIR 1, 2, 3, 4. Callsigns on Air Traffic Control frequencies will either by STATE POLICE (followed by last 3 digits of tail#) or out west they use "BADGE 3". Additionally Aero freqs used will be air/air 123.0, 123.05, 123.9, 123.10. If they are in a search zone they will also call out to aircraft to stay clear on the appropriate Air Traffic Control Freqs. There's 3 MSP Air Unit locations: West (Chicopee Westover), East (Plymouth), North (Lawrence). Each unit takes turns on alert & also monitors the aircraft & weather conditions. IF they see a weather problem on radar they will alert the helo. I'd suggest you take the opportunity at a law enforcement community event that has the helo, to go look at the helo & take a lot of digital pictures