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Old 12-04-2013, 2:55 AM
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Lightbulb Repeater system

Hi, I wasn't sure were to post this. I belong to a volunteer fire department and we have a private channel that we use that is connected to a repeater system, which we are able to talk on county wide with no problems. We are dispatched by our local 911 center, and then once a unit responds were placed onto an operations channels. My fire chief asked me the other day if it is possible to do a simulcast transmission with the operations channel broadcasting over our private channel and our private channel broadcasting over the operations channels. The only reason why we would like to do this is due to poor radio coverage with the operations channels and not being able to efficiently communicate with the local 911 center. Not sure if you could connect the two repeaters together or what you would do. Has anyone ever heard of anything like this, if so what equipment would you need. We tried to have an authorized Motorola/Kenwood radio dealer do this for us, but they kinda were hesitant on the idea.

Thanks
Cody
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Old 12-04-2013, 4:44 AM
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If both channels reside on the dispatch console, the dispatcher could do a patch for the duration of the call ad then break it once it is completed. That is really the only way to make an on-demand/intermittent connection. If it is hardwired then it will be engaged all of the time.
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Old 12-04-2013, 5:43 AM
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There are a lot of those hardwired systems out there, especially in the northeast. You see them more when a department converts to a higher frequency band or to a trunked system and still has pagers on, say, low band. The vendor hard-patches the two together and the low band pagers still hear the traffic. The problem with that is that it wastes the frequency by co-opting it for one-way transmissions to a single agency. It's not illegal, but it's also not spectrum efficient. You hear this on frequencies like 33.86 in parts of NJ and Ohio where it's obvious that the agencies no longer monitor the channel, and different incidents result in a garbled mess with everything dumping over everything else - so the argument that it's for "mutual aid" is quickly negated (it can't be for M/A if no one can get a word in edgewise or the hang-time is transmitted between the units talking on the trunked talkgroup).

If your operations or fireground frequency is in the same frequency band as the repeater, I would advise against patching. First, you would effectively need a "repeater to the repeater." This introduces keyup delays and other things you might not think would be issues, but potentially clip transmissions. You would also need isolation between the receiver and link transmitter. A better solution would be to plot out where the coverage holes are in your district and get those back to a voting comparator that can also vote receivers placed in the holes in coverage in other districts.

It's impossible to cover a large area with one receiver, but departments try to do it all the time and submit interference complaints when the one-receiver system they put on a mountain or a tall TV station tower gets interference from way far outside their intended area of operation. Coverage problems need local points of presence and engineered system coverage patterns.
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Old 12-04-2013, 6:37 AM
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The first thing I have to ask is why the County radio works better than you private radio. If they are not located at the same transmitter site, maybe relocation would be a better solution. If the County's is a large system and has lots of voters than relocation may not resolve the issue. While I whole heartly agree with 902, it can be accomplished if done right, and it can be expensive as you would need at a minimum of 2 voting comparators with priority modules. Each repeater would vote on 2 channels the local and the other repeater. Here is where you have to set it up properly to have each local repeater's receive have priorityand this method is assuming you have access to the County's equipment. There are a few systems set up like this in Westchester County NY so I know it does work. Up here there are even a few X-band systems tied to the County's UHF trunking system.
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Old 12-04-2013, 8:57 AM
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Just because something can be done electrically doesn't mean its legal. There are specific rules in Part 90 (commercial & public safety) regarding rebroadcasting and monitoring both channels for co-channel traffic before you transmit. These rules can vary somewhat depending on your license and frequency band. You can not do this automatically or unattended. About the only way you can legally do this is with a manually operated patch by the dispatcher who will (in theory) monitor both channels before activation.
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Old 12-05-2013, 12:15 AM
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Yes it is possible to tie your local FD repeater into the county repeater system to enhance coverage when needed. Before anything is to be done, you must contact the 911 communications director to see if your even allowed to do this. Then a radio vendor needs to be contacted to go over what kind of system you want. The patch can be remotely controlled or consoled controlled via DTMF to turn it on and off when needed.
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Old 12-06-2013, 7:14 AM
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A quick and dirty way to do this would be to get a couple of CDM mobiles in the bands you need and add a RICK or cheap bi-directional "repeater maker" cable set from EBAY. Use low power on the CDM radios, spread the antennas as far as practical apart horizontally and vertically. If you need "remote" setup and knock down, then a DTMF decoder could be configured for setup/knockdown. This is by no means a "good" or well engineered system and in reality the coverage gaps need to be filled in. But, we support a fair number of agencies that have not migrated to narrow band due to lack of funds. This results in band-aids, some of which would make the Baby Jesus cry if he could see them........... TT
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Old 12-06-2013, 8:30 AM
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Default Remember, your solution needs to be properly coordinated and licensed.

Since some commenters have suggested an RF backhaul or linking solution, and that might be fine (and those resources may or may not be available), I should probably make a statement that deploying an uncoordinated or improperly licensed solution stands the possibility of interfering with other users who share the channel. It's not common, but from time to time, we see the FCC doing enforcement actions which might involve immediate cessation of operation, and, in some cases, punitive forfeitures.

Before an agency deploys a creative system topology that might be fine on ham radio frequencies, it's their responsibility to make sure that everything lives up to the license (including emissions, power levels, antennas, antenna heights, directionality, etc.), and that resource consumptive measures, like "hang-times" are minimized or eliminated. Failing to do so exposes both your agency and you - and could have catastrophic results. That's not always for your agency, but potentially for others you might not be aware of.

Bottom line, plan your deployment carefully and make sure that all your bases are covered. Never put a "blue-wired" contraption on a frequency someone's life depends on.
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Old 12-06-2013, 8:48 AM
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Quote:
Originally Posted by codymw623 View Post
We tried to have an authorized Motorola/Kenwood radio dealer do this for us, but they kinda were hesitant on the idea.
I can see why they are hesitant. When the professionals tell you "Hey, this is a bad idea" then maybe you should take their advice.
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Old 12-06-2013, 9:34 AM
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Quote:
Originally Posted by R8000 View Post
I can see why they are hesitant. When the professionals tell you "Hey, this is a bad idea" then maybe you should take their advice.
It's been my experience that the professionals will tell you why if they think it's a bad idea. I'd be interested to hear the OP's info on that for this proposal.
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Old 12-07-2013, 9:32 PM
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Would it perhaps be a better idea to utilize mobile extenders?

Your private channel (which is apparently a repeater) could be used by your department's members on scene. Mobile extenders can be used to allow portable radios (on a low-power frequency) to connect to your county's system using a high-powered mobile. Licensing frequencies for mobile extenders is relatively easy because of their low power (typically 2 watts). And the existing frequencies in place allowing your department to use the county's frequencies will cover the high-power end of the mobile extender.
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