1. #1
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    Default 800 mHz system questions

    It looks as if my department may be going to 800 mHz in the near future. I've searched the forums and Googled and haven't found quite what I'm after so maybe someone can help me out.

    I'm looking for evaluation criteria of a proposed (as opposed to an installed) system - more from an operational standpoint. I'm having trouble finding something that is 1) understandable by a layperson, and 2) not colored by the claims of salespeople who would be pushing a particular brand/system.
    ullrichk
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    Contact your local Chapter of APCO:

    http://www.apco911.org

    ...and meet in person with some of their members. Your pursuit of information about public safety communication systems is likely a common request for them. Do remember that your questions and answers must be specific to the system in questions, and not merely all about "800 MHz" - a generic pursuit that will offer you precious little.

    Best Wishes,

    Brian

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    Ullrichk, There is not enough room on this page to tell you how BAD the 800MHZ system is....if you like NOT being able to communicate with your dispatch then go for it! If you have any hills in your area then it is NOT going to work that well..If your county or department is going to install more than one tower such as a tower on each hill...then it MIGHT work o.k.
    If you wanna discuss this further you place your e-mail address on here and i'll e-mail you with a number you may call at.
    Thanks


    Keep your VHF or UHF radios

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    Originally posted by chiefmaden
    Ullrichk, There is not enough room on this page to tell you how BAD the 800MHZ system is....if you like NOT being able to communicate with your dispatch then go for it! If you have any hills in your area then it is NOT going to work that well..If your county or department is going to install more than one tower such as a tower on each hill...then it MIGHT work o.k.
    If you wanna discuss this further you place your e-mail address on here and i'll e-mail you with a number you may call at.
    Thanks


    Keep your VHF or UHF radios
    What we have here is a textbook example of a person who has been the victim of a poorly designed and implimented 800Mhz trunking system. There is no phrase that holds more true in radio system design than "You put garbage in, you get garbage out"

    First of all, there is no such thing as "the" 800Mhz system. There are many different makes and models of 800Mhz trunking systems.

    A properly designed 800Mhz trunking system will work just as well if not better than a conventional system we are all used to. The problem is, that very often doesn't happen. These systems are VERY expensive. What usually ends up happening is the system is designed around a budget and then cut back even more after the plans are made to save more money. The result is poor coverage, dead spots, busy signals, etc.

    If you design a system that will meet the needs now and for the next 20 years, with talk-out and talk-back coverage that covers your entire area, you won't hear complaints like the one expressed above.

    When you get into the details of radio coverage, you will hear percentages thrown out. You need to find out if it is PORTABLE talk-back or MOBILE talk-back. If they tell you 95% Mobile talk-back, chances are it is only 50-60% portable talk-back. They don't tell you that unless you really pry and for us, portable radios are a lifelines.

    If your area is not conducive to easy radio coverage, it makes the system get very expensive very quickly. You need receivers all over yin-yang to make talk-back adequate, and you need simulcast transmitters to make talk-out cover your entire area.

    It's a lot of money, but when done properly, it will work well.
    Last edited by nmfire; 12-07-2004 at 12:23 PM.
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    nm

    When is 800mhz appropriate tech choice (in general)?

    We are tiny rural dept that has coverage in parts of 2 counties. 911 Dispatch center in each county. As a 911 dispatch in the the nearest "city" to us (7mi). All commo, voice or pager, currently VHF. Apparently the city the handles our dispatch has grant $ coming to install an 800mhz system. I fail to see why is needed or appropriate (and they are planning going to layoff their 4 fulltime firefighters to ave $). May force us into changing our dispatch.

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    Nmfire, can talk-backs be caluclated, or are they based on empirical testing? Does it typically include building interiors or just "road frontage"?

    Our situation is that we (the county, anyway) got a wad of money from DHS for communications interoperability. We now have 800 mHZ trunking radios (reconditioned) for every emergency vehicle in the county. There are two trunking systems available to us; one owned by the SO, and the other a commercial system.

    There has been some serious discussion of changing to trunked 800 mHz for primary communications. I'm out of the decisionmaking loop in this matter, but I want to make sure that anything we wind up will be adequate for our needs.

    Lots of good info at the APCO site, by the way. Thanks for the input so far.
    ullrichk
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    I am very aware that there is no creature called a 800mhz system and that they are trunking systems. When i am in a basement fire and i cannot talk to the officer outside there is a problem. My main concern is to those that are looking to go to a 800 trunking system is dont let the manufacturer pressure you into what they tell you is a good system. They are not the ones that have to use it you are. Have whoever the powers to be are make certain that they do substantial tests prior to buying...and yes we do have a poorly designed system, it was our back-up system but it is now our primary. And also i guess that it is i have always been raised on and i was raised on a VHF repeater system that i would highly reccomend over the 800 trunking system

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    Chiefmaden -

    My work email is in my forum profile.
    ullrichk
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    The advantage of a trunking system is you can have a lot of different users on a small amount of frequencies. Before, you needed as many repeaters or simplex channels as you had agencies and it went up exponentially if an agency needed more than one channel. So you have the police on a bunch of channels, the FD on a bunch of channels, public works on a channel, schools on a channel, parks on a channel, blah blah blah. Not everyone is talking all the time so it is a lot of wasted channels that sit idle more often than not. However, they are needed when you need them so they can't just not have them at all.

    What trunking does is take a pool of repeaters (say 5 or 6) and dynamicly assign them to groups of users on as-needed basis. The user's radios are programmed for "talkgroups" which are virtual channels. When someone on Talkgroup A presses their PTT button, the computer system receives that request to talk, picks and appropriate available repeater, and steers all of the radios on talkgroup A to that frequency. When the transmission is compete, the repeater is again available to the next person wants to talk on any given talkgroup. Since the talkgroups are "Virtual Channels", you can make up as many as your want to give to as many different users as you want. Since most users other than PD & FD are light on radio traffic, it hardly adds to the loading at all. This is great for cities and such because of the need for many many radio users on seperate talkgroups. It is NOT efficient for a little rural town because there is just no need for that amount of communication. Now, if your little rural area's communication is handled by a big metro center that does use it, you might be forced onto it. Then you have the problem of the rural area not being factored into the system design from the begining. Isn't this fun!!

    Can talk-back be calculated or is it based on emperical testing? The answer is "yes" There are calculations for it and believe it or not, they have names. I just don't rememeber it off hand. There is software that uses the calculations based on topographic data and user entered parameters to map out what will work where. However, software can only take into account so many variables. There is a lot of seat-of-the-pants testing and simple "I know this won't work here" based on experience. It is not easy.
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    I forgot and wanted to add some more stuff you should look into when they tell you their master plan.

    Portable radio talk-back has severl variations that all effect how far your signal will go. In order from "best" performance" to "Least performance"....

    Holding the radio in your hand, vertical on the street.

    Radio on your waist vertical with a speaker mic.

    Either of the above inside a light construction residential structure.

    Either of the above in a heavy commercial structure.

    Now your going on fire attack or a search crew... put the radio in a coat pocket or under your gear and crawl through a building. That radio is now:
    Horizontal rather than vertical which creates loss in and of itself due to everything else being vertical. It is against your body which creates loss and then your crawling so the signal has you above it and the floor below it. Then you have bunker gear thrown over it which pushes the antenna right against you which increases the loss. You know those nice little stubby low profile portable antennas? Those look cool but do cut down on your signal for both TX and RX.

    So what does all that mean? If they tell you "This has 90% portable talk-back", find out what state that portable is in. If it is stnading on the street holding the radio in your hand, you can slice that 90% up pretty bad by crawling through a building.

    And that brings me to my next point... interior fire attack should never, never, never, ever be conducted on a trunking talkgroup. The system should include a few analog simplex/direct tactical channels for that. That is an NFPA standard too, not just my own preaching.
    Even the burger-flippers at McDonald's probably have some McWackers.

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    Originally posted by nmfire
    [B]What we have here is a textbook example of a person who has been the victim of a poorly designed and implimented 800Mhz trunking system. There is no phrase that holds more true in radio system design than "You put garbage in, you get garbage out"

    First of all, there is no such thing as "the" 800Mhz system. There are many different makes and models of 800Mhz trunking systems.

    A properly designed 800Mhz trunking system will work just as well if not better than a conventional system we are all used to. The problem is, that very often doesn't happen.
    ullrichk...

    While all participants in this thread are trying to be helpful, the post by nmfire truly says it best. While recognizing the passion of others, please don't be guided in any of your decisions by posts from non-technically qualified persons - whether they be at the firehouse or in this forum. The only generality worthy of repeating in this thread is that you have to diversely network among professionals before you make a decision.

    Brian
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    Default 800 MHz system

    This is the home page for our county-wide initiative. I am sorta-kinda involved as I am a radio-head (Ham radio Operator).
    If you have any questions, drop me a note

    http://www.co.ramsey.mn.us/cm/psradio/index.asp

    Jim Mc Carthy, RN-C, FF/EMT
    White Bear Lake FD

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    We just moved to the 800 system after much fight. We were happy with our high band system that worked flawless and in our area the 800 has alot of dead spots. Also in some of our most criticle buildings like our pump storage project the 800 system doesnt work.

    We now operate with all trucks and officers carrying 2 radios. They carry 800 and high band radios. We the firemen carry our high band and work off our own internal fire dept frequency and can only talk with officers and our selves and dispatch only works off the 800's which our officers and trucks carry. Its kind of a pain it would be nice to have one system that is sound but thats the cards we where dealt.

    So we carry high band pagers, because out 800 system doesnt have a paging system. Can only talk to dispatch on our 800's and all firemen talk on our high bands because of the solid radio coverage. Heh pretty dumb way to work but it works well for us in this situation..

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    Yea, unfortunately, there is no such thing as an trunking pager. The only way you can "page" on a talkgroup is with an actual portable radio. That can be pretty expensive and suffers the same weaknesses of the rest of the system as far as coverage.

    Most places that still use voice paging and have gone trunked will simulcast the dispatch traffic on the "old" system for the pagers.
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    My township is forcing the trunking system down the fire and EMS service's collective throats without really hearing any of our concerns, but that's not why I'm writing. I would like to know if IDs can be set to be non-repeated and vice versa. We currently have four repeater channels for our fire and EMS communications to dispatch. But we have six "fireground" channels that are designed to be used as short-range communications. For example, interior crews to command or any other unit on the fireground. Currently, these channels are shared by multiple departments, but it is okay because of the short-range nature of the channel. Will a similar form of these channels be available on a trunk system or will every fire buff and other company hear everything that is going on your fireground while operating on the other side of the township?

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    For what it's worth, I'm not opposed to having 800 mHz trunked radio in my jurisdiction, but if that's what we are getting, I wan't to make sure it will be properly designed so it will do the job.

    My biggest fear is that we'll be getting a bunch of equipment that has been thrown together and not designed by a competent professional.
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    Originally posted by turkyman
    My township is forcing the trunking system down the fire and EMS service's collective throats without really hearing any of our concerns, but that's not why I'm writing. I would like to know if IDs can be set to be non-repeated and vice versa. We currently have four repeater channels for our fire and EMS communications to dispatch. But we have six "fireground" channels that are designed to be used as short-range communications. For example, interior crews to command or any other unit on the fireground. Currently, these channels are shared by multiple departments, but it is okay because of the short-range nature of the channel. Will a similar form of these channels be available on a trunk system or will every fire buff and other company hear everything that is going on your fireground while operating on the other side of the township?
    This is what I meant by a simplex channel. Yes, you can have those on 800Mhz just like you can with any other band. In fact, you MUST have them in my book and they should be what you use for interior fire attack.
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    I agree with you about them being a necessity. And thanks for the additional information.

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