Originally Posted by mcrismon
What is MFD channel 4 used for? I always thought they used that channel for LZs. I keep hearing them send Gilbert units to that channel, but I also hear them being sent to channel 3 as well. Also, does anyone know what the "pre tone" sound is I hear sometimes before the normal dispatch tone is played? Its usually a Hi-lo sound, or lo-hi sound followed by the normal tone.
Channel 4 on the Mesa Fire System has nothing to do with the old VHF Ch4 (154.280) Mutual Aid channel that is used for landing zones. That is now handled on Mesa's turnked Ch14 which is patched when they need it to VHF mutual aid.
The current use for the trunked Ch4 is the same as Ch3 which is mainly for medical type calls. I think they added it to give a little more breathing room for medical calls since they get more of them then they get structure calls or major medical calls.
The pre tones should be the station tones to open the speakers at the ambulance locations most likely. Those are still listening on the old VHF Ch1 154.340 I think.