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6.25 kHz bandwidth digital modulation radios are not manufactured within the next one or two years. 3.1.2 Covera2;e Relief The main problem in regard to radio coverage is talk-out from fixed location radio sites, particularly to handheld portable radios worn on the belt inside buildings. The only way to overcome this problem is to increase the number of fixed location transmitter sites. Unfortunately, it is generally not possible to have two transmitters on the same frequencies transmitting at the same time. This means that either the dispatch center must use some means of control, automatic or manual, to select a single transmitter to transmit out to part of the geographic coverage area required or an expensive electronic method called simulcasting must be employed that would permit two or more transmitters to transmit the same message at the same time. Automatic or manual selection of a transmitter is unacceptable from an operation perspective. Therefore, the coverage difficulties can best be significantly relieved by increasing transmitter sites and employing simulcast technology. 3.1.3 System Reliability Concerns The reliability concerns are related to three different areas which are: the need for a back-up dispatch center; the need for reliable communications links between the dispatch center and fixed location radio sites; and the need for overlapping coverage in the event that a primary site is out of service for any reason. A back-up dispatch center can be provided, as described earlier in this report, for a relatively low capital investment. The back-up dispatch center will be required regardless of which alternative is selected for overall radio communications improvements. The communications links between the dispatch center and fixed location radio sites are best served by employing microwave links. Microwave links are relatively expensive, and generally cannot be justified on a cost basis over the savings by eliminating the cost of telephone lines in any reasonable time period. It may be possible, however, to utilize the existing MnJDOT radio system microwave network that goes through Anoka County and that might interconnect more than half of the fixed location radio sites that may be required for adequate coverage to the dispatch center in Anoka. The additional sites might be tied in through relatively inexpensive spur microwave links or those sites may still be links to the dispatch center leased telephone lines, however, whether the system is interconnected over microwave and/or telephone lines, the fixed location radio stations must be controllable by means of in-band tone signalling rather than DC signalling. The coverage difficulties can be relieved with proper design when the simulcast system is laid out so that there is reasonable coverage with anyone site being out of service. Ronald Vegemasl Engineering. Inc. -24- Report: Anoka County