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  1. #1
    Forum Member martinm's Avatar
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    Oct 2001
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    Northumberland, United Kingdom
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    Question Looking for opinions

    The Police service I dispatch for is about to undergo its biggest change as far as comms is concerned in its history. We are moving from UHF/VHF systems, to digital trunked communications. As ususal, the comms staff are the last to hear about the benefits/pitfalls of the system we will be using in a few months and was wondering if anyone here has experiences, goor, or bad they would feel like passing one. The biggest change as far as we can tell, will be the use of talk/sub groups for different users. How do you utilise this? Also, how do you find the system as far as clarity of transmissions, do you get dead spots as we do with UHF/VHF? We are also getting a mobile phone/paging system with this system. Any comments about having all your eggs in one basket?
    United Kingdom branch, IACOJ.


  2. #2
    Junior Member
    Join Date
    Aug 2002
    Location
    Miami, Florida
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    Default Simplex

    One question to ask loud and clear: How will simplex (a.k.a. talk-around) work?

    If you're used to on-scene communications going between radios directly, i.e. not through the repeater, then get ready for a whole new world.

    Youíll hear many debates about 450 vs. 800 MHz, but in my opinion, the real difference is this lack of direct communications in most 800 MHz systems. If the FF on the floor in the basement needs to get up and go outside to be heard by Command outside the building, you need to re-think this. NO system, 150, 450 or 800 MHz has 100% coverage. You need to ask about how things will work on the 1-2% of the locations where units wonít be able to access the system. Donít be surprised if the only answer is Ďtell the unit to moveí.

    I know of at least one agency that got a wavier from the FCC to permit conventional simplex channels on their otherwise trunking system. This, to me, is a good compromise. The units on the simplex channel will not be able to hear the dispatcher, but at least theyíll hear each other.

    As for the Ďall eggs in one basketí problem in public safety, I think you know the answer already. When you look at the system, look for common points of failure. If thereís any one device, one channel, one building, one power source, one fiber, one tower that touches all of your possible dispatch methods, itís time to step back and ask a lot of Ďwhat-ifs?í A lot of potential problems can be handled well with totally redundant systems in totally redundant sites. Of course this can up to double the infrastructure costs. Having a secondary system thatís totally independent, maybe even public sector, might make sense. Just make sure that it never becomes the primary system. Itís not hardened for Public Safety.

    Good luck with the system.

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