Conventional radio and the way it is used and managed within a jurisdiction presents its own particular problems. Can the county emergency management agency talk to the law enforcement, or the fire department?
The Emergency Operations Center may, but not always, have a radio for each of the agencies within the jurisdiction. But then a relay will be required, which is certainly better than nothing for agencies to communicate with each other.
Another question: Are the repeaters that serve the agencies within a jurisdiction located in places that will provide the required coverage? Often not. This is very difficult to do, geographically, and when this is possible it is sometimes cost prohibitive. Mutual aid units can be a problem also. Different frequencies or bands and the lack of spare radios can render communications with mutual aid units impossible.
During the final stages of a large scale federal incident, a demobilization official decried the fact that he was driving a mile or so several times a day to gain access to a cell site from his vehicle because his agency's local VHF communications system had been destroyed during the incident. There were at least two VHF ACS systems that covered both his demobilization camp and headquarters.
Trunking radios are controlled by a microprocessor in the the radio, the multiple repeaters (up to 28, which often makes the system cost prohibitive) and in the controller within the system. Up to 150 radios can be assigned to each repeater without overloading the system. They are assigned in groups (or fleets or systems) and sub-groups (or sub-fleets or sub-systems). In this way there can be, say, 10 supervisors with up to 14 subordinates on each repeater. Each supervisor can talk to the other supervisors and to their own subordinates. None of the subordinates under one supervisor can talk to the subordinates under another supervisor. Only one contact between any two stations can occur on any one repeater at a time. When one repeater is busy, the controller will automatically assign the other radios to another repeater. This is the big advantage trunking radio has over conventional radio. The Police Chief can talk to his organization as well as to the Fire Chief, Emergency Management Director and the Dog Catcher, but none of each organizations personnel can talk to another organization's personnel. These systems operate in the 800 - 900 Mhz frequency range. Therefore bending or refracting of the signal around or over hills, ridges or buildings, relative to VHF or UHF signals, is minimal. Penetration through buildings and dense foliage is also greatly reduced. Some examples demonstrate this.
Continues next week.