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1996-97 EMCOMM Bulletins

TO: Emergency Communications Units - Information Bulletin
TO: Emergency Management Agencies via Internet and Radio
FROM: Auxiliary Communications Service (ACS) of the California Governor's Office of Emergency Services 

Back

EMC093 - Uses for Amateur Radio - 6/7

8/18/1997

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Subtitle: Trunking Problems

A county converted all its radios to a 800 Mhz trunking system. The system was installed and operating just fine during the winter. 
That spring, all the leaves came out on the trees and there were so many areas in which the radios didn't work that the county considered the trunking system much worse than the older conventional systems. Another county in the foothills and mountains attempted to convert to a 800 Mhz trunking system. The coverage was so bad that they ended up keeping both the conventional and trunking radios in their inventory. A third county converted to 800 Mhz trunking and the handheld radios (3 watt max) would not work between each other or to vehicles outside from within a government building. There is a very expensive way to minimize these types of problems in many but not all areas. Basically it is to install multi-sited systems with simulcasting. These multi-sited systems have to be linked together. This can be done by microwave or landline. Where have we seen this before?

There is also a digital "handshake" going on between the radio and the controller via the repeater constantly. If this "handshake" disappears on the radio side, that radio cannot communicate with the system or any other radios on it. If the "handshake" fails within the controller then the system is supposed to automatically start operating similar to a conventional type system. However this can also fail and all communication between all radios can be cut off, totally. This digital "handshake" can also be affected by very heavy rain or dense smoke as well. Complete coverage of the jurisdiction by repeaters is even more difficult and expensive than with conventional systems.

There are also three or four different types of trunking systems out there. And none can communicate with another even when they operate in the same frequency range. They have different digital "handshakes". Some of the radios can only be programmed as trunking and cannot even have a conventional simplex channel programmed in. These last two items makes it a more than a little tough to provide mutual aid units to each other. And none can provide mutual aid units to any jurisdiction with a conventional VHF or UHF radio system. Some trunking radio system owners are under the misconception that their conversations are private. Well, unless they have scrambled audio capability in their system (very, very expensive), any set of correctly programmed scanners capable of operating within the 800-900 Mhz frequency range can pick them up. There is also a new scanner on the market whose manufacturer claims that it can track and monitor the trunking systems.

Continues next week
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