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  1. #1
    MembersZone Subscriber ullrichk's Avatar
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    Question Radio Comm. supervision equipment

    I'm not a radio guy and our local radio service hasn't been much help on this:

    What options are evailable to monitor radio systems (VHF in this case)for power loss and transmitter/repeater failure? The comm. center needs to be notified of failures visually and audibly without capturing the radio frequency.

    I could look at manufacturer's websites if I knew what I was looking for (at leat what it's called).
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  2. #2
    Forum Member nmfire's Avatar
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    Well, this can be remarkably simple and inexpensive or remarkably difficult and costly. I need to know how your dispatch center is connected to the remote transmiter/receiver site. This will determine what your options are. It would also help to know what the make/model of the repeater is and how the site is powered.

    The simplest way to signal that there is a problem at the site is over-the-air. Many commercial repeaters have an alarm input terminal. Usually it is a ground or contact closure. This can be triggered by any number of devices that monitor line/generator power, forward and reflected RF power, voter troubles, etc. Triggering this input will make the repeater send a periodic tone over the air alerting dispatch and/or field units that know what it means that there is a problem at the site. This is hunky dory as long as the site has backup power for some amount of time and it isn't the transmitter and/or antenna that has crapped out. If the transmitter or antenna are toast, that kind of self-degates the over-the-air alarm.

    If you don't want to ise Over-The-Air:

    If you are using a microwave link, you can use a microwave channel to send the alarm signal back to dispatch.

    You can also use a system with a modem that will call out and report the alarm to dispatch, or even dial a cell phone or pager. I'm trying to find some example but I can't for the life of me remember who makes it.
    Last edited by nmfire; 05-09-2005 at 06:18 PM.
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    Forum Member martinm's Avatar
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    The comms centre I workd at has an audible sysem which operates when the power goes down at a remote mast site, as well as a small TV type monitor which displays all 12 of our mast sites at once with their current status and a further alarm to tell us the generator back up has swung into action. If you only have one or two masts coverign your area, you may want to look into a UPS back up, where the power comes from another source, other than the local electricity sub station.
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    Forum Member Weruj1's Avatar
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    we are using some ancient thing called Farscan........ dont know jack about it .....may wanna try and post this in the dispatcher forum also.
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  5. #5
    MembersZone Subscriber ullrichk's Avatar
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    nmfire-

    Thanks for your help.

    I'm not sure how detailed an answer you need for clarification, but I believe the console uses a rack-mount equivalent of a mobile radio with a broadcast antenna on a mast at the dispatch office. They transmit VHF to a remote repeater (make and model unknown to me) and then VHF to stations/pagers/mobile radios.

    We currently have UPS with a manual-start generator at the repeater site with on-the-air alert of power outage. I'd really like to see off-air monitoring of power AND signal.

    Is the monitoring capability I'm thinking about in any way related to the SCADA systems that are commonly used for monitoring utility company operations?

    As an aside, we will be simulcasting on VHF and 800 MHz trunking soon. Originally the plan was to be a cross-band repeater at the remote VHF repeater site, but I think we're working toward true simulcast from the console.

    FWIW (if you haven't already guessed) this is all ISO related stuff.
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  6. #6
    Forum Member nmfire's Avatar
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    Ok, so nix all that OTA stuff I mentioned sine you are already using that.

    What do you mean you say you want to monitor the "signal"? Are you just saying you want to make sure that it's actually transmitting or do you want to just alarm if the forward & reflected power are out of spec indicating a problem?

    Does you dispatch center have a central station alarm monitoring computer that is used for municipal fire & burglary alarms? If it does, then life is easy. You can install simple burglar alarm at the radio site for all of about $200.00. Connect the various alarm triggers to the alarm system and program them as supervisory alarms that will report to your alarm terminal at dispatch. That's super-easy and will give you burglary, fire, high & low temperature, forward & reflected power (once you buy the equipment to sense that), line power, generator power, etc.

    To indicate to the dispatcher that their transmission is actually going out through the repeater, simply put an old mobile radio in the dispatch room (put an antenna outside if need be) and turn the volume down. You can either look at it to see that the busy light on or you can put a bigger LED on a COR output of the radio.
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    MembersZone Subscriber ullrichk's Avatar
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    The supervisory alarm method looks like it's a route we'd want to pursue. We need to know if the repeater is transmitting plus power status. The burglar alarm for the repeater site would be a plus as well.

    Now I just have to talk to our radio service so they can tell me why it won't work. . . (Sometimes I think they're out of their league, but generally they are good to us.)

    Thanks again for the help, nmfire.
    ullrichk
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  8. #8
    Forum Member nmfire's Avatar
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    Yea, I know how you feel.

    The alarm system thing will work great as long as your dispatch center has the central station receiver. If not, it would have to go to a commercial alarm company and they would have to call the dispatch center. I wouldn't want to rely on that.

    I made my own power monitoring system with delayed relay. Since the tower site has an auto start full-load generator, all I really care about knowing right away is if it failed to start or switch over. I set the relay to delay contact closure for one minute. If after one minute the generator hasn't kicked on, it will trigger a supervisory alarm on the firehouse alarm system. I'm going to be installing a high & low temp alarm on it this summer as well. The temp monitor is only about $50.00 max and it can really save your ***.
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