Building a repeater for high band VHF public safety

[WuLabsWuTecH]

Hi All,

We have had a recurring problem at my fire department that is getting worse recently. Since the tower that the county dispatches us from is located so far away, by the time it gets to our little village, the signal is weak. This is not a problem if we are at our station since we have a large antenna mounted on top, nor is it a problem at the edges of our village. However, we have some taller (read: 4-5 stories) in our village and when we are in these buildings, our pagers don't receive and won't trip on a dispatch.

Since we have an antenna already setup, how hard would it be to set up a repeater to rebroadcast the pages to the area surrounding our station? This would just be a low power thing, and hopefully it's a low budget thing I can do myself with the equipment we have lying around the station unused and/or a trip to radioshack. The coverage area would be small--about a football field's footprint, maybe two side by side--as that's the only area we're having trouble with, but since we are located right in the heart of the village with these buildings surrounding us, these businesses/restaurants are where we spend a lot of our time outside of the station.

So.... Is this doable either with the equipment I have in the station and/or something that I could take on as a personal project?

And to answer a question that might pop up--the reason this isn't a problem when we are on runs is because each of our fire trucks has a professionally built repeater mounted on it. Once we start the truck, our reception improves markedly. Unfortunately, we can't just keep a truck running all the time, and Chief does not want to buy another professionally built repeater just to cover a small chunk of the village. Unfortunately, with the coming of summer and volunteers spending more time out and about, this had led to a significant number of members not responding to runs lately.

Thanks,
-Wu

 

[jim202]

Hi All,

We have had a recurring problem at my fire department that is getting worse recently. Since the tower that the county dispatches us from is located so far away, by the time it gets to our little village, the signal is weak. This is not a problem if we are at our station since we have a large antenna mounted on top, nor is it a problem at the edges of our village. However, we have some taller (read: 4-5 stories) in our village and when we are in these buildings, our pagers don't receive and won't trip on a dispatch.

Since we have an antenna already setup, how hard would it be to set up a repeater to rebroadcast the pages to the area surrounding our station? This would just be a low power thing, and hopefully it's a low budget thing I can do myself with the equipment we have lying around the station unused and/or a trip to radioshack. The coverage area would be small--about a football field's footprint, maybe two side by side--as that's the only area we're having trouble with, but since we are located right in the heart of the village with these buildings surrounding us, these businesses/restaurants are where we spend a lot of our time outside of the station.

So.... Is this doable either with the equipment I have in the station and/or something that I could take on as a personal project?

And to answer a question that might pop up--the reason this isn't a problem when we are on runs is because each of our fire trucks has a professionally built repeater mounted on it. Once we start the truck, our reception improves markedly. Unfortunately, we can't just keep a truck running all the time, and Chief does not want to buy another professionally built repeater just to cover a small chunk of the village. Unfortunately, with the coming of summer and volunteers spending more time out and about, this had led to a significant number of members not responding to runs lately.

Thanks,
-Wu

Before much can be done on your dream project, bear in mind there are both technical and legal issues here.

You have provided ZERO on any details of just what the vehicle repeaters are.

What are the exact frequencies are being used right now? In band repeaters will cause problems and the further apart the frequencies being used are the better off the system will play. You may even have to install filters on the antenna connections on the vehicle repeater.

What FCC license are they operating under?


What frequency is your current radio system working on?

The reason for all the questions is it doesn't take much to cause interference to a receiver when you start adding new transmitters. It also depends on where you mount the new antenna for your low powered repeater.

Don't forget that any new transmitters you put on the air after getting the FCC license modified for it's operation will have to be narrow band compliant.

You have a number of hoops to jump through before you can take the first step. That should be getting the blessings from the fire chief.

 

[KC8ESL]

Sounds to me like it is a city council matter. Once you start tossing out terms like "safety issue" and "inadequate fire protection zone" they'll be prone to perk their ears up. Be ready to answer the question of "Why is this just becoming an issue now? Our radio systems are xx years old." You will be grilled and it won't be pretty.

Just make sure you get your chief's permission before you take the issue up, that really sounds like it would be his battle, or whomever he appoints to do it for him.

To further add questions:

Do you just want to hear re-broadcasted fire pages from dispatch?
Do you hear just fine but can not relay information back to dispatch?
Are you trying to do something with the fireground channels?

Anything you do requires fcc license modification.

Does the county send out the pages? Perhaps it should be looked into that they check the transmitter site or increase their output power?

 

[quarterwave]

Short answer is NO.

There are no personal projects in public safety radio. Your device, as well thought out and executed, could cause other issues, even if logical licensing and technical specs are followed, without planning and involvement of your County/Town/Agency's radio resource.

A low power store and forward system may work, but the above posts bring up the issues your radio people are going to need to address.

 

[cabletech]

Also, anything "off the shelf from Radio Shack" will not work. Radio Shack is no longer a 'radio' store.

You will needd to work with a local commerical radio shop.

 

[WuLabsWuTecH]

So first off, I don't have a lot of knowledge in radio. I do have a Bachelor's in Engineering and I'm willing to learn, but let me try and answer your questions one by one:

@Jim: I provided very little details because I know very few details unfortunately. I believe our dispatch frequency (which is the only one we need) is 460.175? Or something close to that.

The vehicle repeater is a box about the size of the mobile radio that is made by motorola. It works by allowing a set of our walkies to work even when we are out of range of the normal walkies. Basically, we have a couple of walkies that are set such that they can only transmit/receive on whatever frequency the truck's mobile is set to.

We have a couple of FCC licenses in our station. The dispatch would probably be on the county's license, but we have 2 additional licenses. One of the frequencies we have licensed us currently unused (it was our old backup dispatch channel but we no longer have 2 dispatchers).

@KC8ESL: City Council did discuss it, but it was determined we have no money for building a new tower right now. It has nothing to do with the feasibility of it, but all about the money. We laid off 2 of our 6 full-timers recently so I do not doubt they do not have the money to put in a base station/new tower/whatever was discussed in the meeting.

The LT in charge of communications told me that if I can figure out a way to do it for cheap, we could probably get the council to approve it. I would assume that LT has already talked to chief about it and has his blessing since he was also doing research on how to solve the problem. The issue is coming to light now since more people are spending more time in the radio "dead zone." Due to us losing full-timers, we're trying to keep volunteers closer to the station so our response times don't get horrendous. Unfortunately, our station is in the middle of the dead zone. Member's homes are not. Full-timers are required to stay on station except for lunch so it was never a problem for them.

We don't need FG ops or tac channels. We just need to hear the dispatches. We have no trouble transmitting, because once we start the truck, we have a repeater that also goes on.

@ everyone else: I know that for low power transmissions, there are exceptions that don't require an FCC license. I also know that since we have an FCC license already for a channel that we are not currently using, we can probably transmit over that without issues. I was hoping I could build a low power device that would completely be exempt from FCC licensing just to make things simple, but perhaps I'm mistaken about low power transmissions not needing licensure? I'm literally talking about needing to be able to transmit to the 2 buildings to the left of the station, the 3 buildings across the street, and the one caddy corner from us. i know that there are kids toys that allow them to transmit radio signals on either AM or FM radio, so I figured there should be a device I could find with a similar exception?

Thanks for all the info guys!

 

[WB4CS]

So first off, I don't have a lot of knowledge in radio.

In my opinion, that's where you should stop.

Kudos for wanting to do it on your own, and if this were an amateur radio station I would support you fully 100% on the idea of going at it on your own. However, when dealing with public service frequencies and equipment it would be in the best interest to let a commercial radio shop help you out.

Without proper knowledge of exactly what you're doing, what equipment you're using, what frequencies you're licensed for (exact frequencies) and the location of the transmitters in relation to neighboring departments, your low power station could end up causing severe interference to other agencies close or far away. You may not even be aware that you're causing interference until the black SUVs with direction finding radios pull up in your driveway. When dealing with public service radios there should be no "probably" and "I think" involved.

A commercial radio shop will be able to get you something up and running that will work how you need it. That's just my opinion, and if you go at it on your own, I wish you luck!

 

[quarterwave]

Also, anything "off the shelf from Radio Shack" will not work. Radio Shack is no longer a 'radio' store.

You will needd to work with a local commerical radio shop.

Isn't that the truth. When I go in for parts I always ask when they are changing the sign to Phone Shack, since cell phones are all they care about. Far cry from what they were when I worked there in college. There's not a guy in there that knows what a relay, an SPDT switch or a transistor is.

 

[quarterwave]

In my opinion, that's where you should stop.

Kudos for wanting to do it on your own, and if this were an amateur radio station I would support you fully 100% on the idea of going at it on your own. However, when dealing with public service frequencies and equipment it would be in the best interest to let a commercial radio shop help you out.

Without proper knowledge of exactly what you're doing, what equipment you're using, what frequencies you're licensed for (exact frequencies) and the location of the transmitters in relation to neighboring departments, your low power station could end up causing severe interference to other agencies close or far away. You may not even be aware that you're causing interference until the black SUVs with direction finding radios pull up in your driveway. When dealing with public service radios there should be no "probably" and "I think" involved.

A commercial radio shop will be able to get you something up and running that will work how you need it. That's just my opinion, and if you go at it on your own, I wish you luck!

To the OP: I think this is all sound advice. I have worked in Telecom/Radio for 23 years and I would not touch a "personal" project on a public safety system without full involvement of a radio shop, not because I can't do the work...I can...I can have a repeater ready in a matter of hours, straight from the spare parts cabinet at home...but the point is, no matter what you know or can learn, that's not the place to start messing around. From a professional radio persons point of view, and as expressed above, from the Amateur radio point of view...take it from us....you need help. We know it's not lack of brain, but there is more at stake. As I have said when taking on many projects that have previously failed....they didn't know what they didn't know.

 

[KD0LWU]

Let's try and attack this from another vantage point.
You already have the licence for the other frequency, you were using equipment to operate on it, and probably still have it somewhere? Why not get with the company that set up your existing system and see if it's something they can do for a reasonable amount of money with that existing equipment?
I agree, I think it's a bad idea for you to personally attempt to work on anything in the public service sector, any number of things can go wrong and mess the entire system up! But even on your own, you are looking at several thousands of dollars in equipment, even low power, to do it right. BUT, if you have existing gear, on an existing freq. I don't think it should cost all that much to get something usable set up for what you need.
Just another way to go about it? It sure wont hurt to discuss this with them and ask what is doable. Make sure you explain the problem fully, and make sure they understand the financial situation you are in! But I'd imagine you're community has done a lot of business with them and they would like to do more in the future!
Good luck!

 

[902]

Public safety frequencies require frequency coordination and a license. This is a show-stopper. You will need to get the "concurrence" of the authority having jurisdiction (the licensee) to set ANYTHING that's not licensed up on the frequency pair they are using. Without that in writing, you will have spent your money on a license application that will go nowhere because it is opposed by one or more of the coordinators.

There are a number of different methods, but in order to proceed with any of them, please recall your project management coursework. First, you need to clearly define what your problem is - including the delimiters that go with it, then go about identifying the various methods you have at your disposal.

Since no two systems in public safety communications are alike, you will need to address the unique issues within your community and the system which serves it.

Some alternatives for consideration may include synchronous simulcast (it's probably the most seamless, but also the most expensive, as you need connectivity, a master clock that's usually referenced to a rubidium or cesium standard on each transmitter, and precise control of phasing launch), store-and-forward (which will be a nuisance and may hurt communication rather than help it), a low power auxiliary transmitter at your fire station activated by the communications center specifically for sending tones and voice announcements - these days that's fairly easy using two Telex Vega IP-223 modules back to back on a VPN, or some hybrid solution. Experimentation with intentional RF emitters may cause interference and will be an excursion from the FCC Rules.

Either way, you won't be able to pull a solution out of a dumpster... and if you do, you may cause harm. Remember, everything in public safety should be coordinated and licensed.

 

[WuLabsWuTecH]

In my opinion, that's where you should stop.

Kudos for wanting to do it on your own, and if this were an amateur radio station I would support you fully 100% on the idea of going at it on your own. However, when dealing with public service frequencies and equipment it would be in the best interest to let a commercial radio shop help you out.

Without proper knowledge of exactly what you're doing, what equipment you're using, what frequencies you're licensed for (exact frequencies) and the location of the transmitters in relation to neighboring departments, your low power station could end up causing severe interference to other agencies close or far away. You may not even be aware that you're causing interference until the black SUVs with direction finding radios pull up in your driveway. When dealing with public service radios there should be no "probably" and "I think" involved.

A commercial radio shop will be able to get you something up and running that will work how you need it. That's just my opinion, and if you go at it on your own, I wish you luck!

To the OP: I think this is all sound advice. I have worked in Telecom/Radio for 23 years and I would not touch a "personal" project on a public safety system without full involvement of a radio shop, not because I can't do the work...I can...I can have a repeater ready in a matter of hours, straight from the spare parts cabinet at home...but the point is, no matter what you know or can learn, that's not the place to start messing around. From a professional radio persons point of view, and as expressed above, from the Amateur radio point of view...take it from us....you need help. We know it's not lack of brain, but there is more at stake. As I have said when taking on many projects that have previously failed....they didn't know what they didn't know.

Thanks guys. I agree with you that I need to learn a lot before I even attempt to do something like this, and if I do try something, it's not something that's going to be done tomorrow but over the next few months.

I was under the impression though, that there were bands allocated for people to just experiment with. The receiving equipment is all already in place and I can very easily hook into that antenna without causing any issues. This antenna is mounted on the station. It's getting it out to another frequency that I worry about and where I get hung up on. I *thought* there was a band in AM/FM where kids were allowed to play on etc. I know that my father (who was very into radio and this kind of stuff when he was a teenager) said that most countries have a band that's allocated for whatever anyone wants to use it for. Of course he's from Asia...

 

[WuLabsWuTecH]

Let's try and attack this from another vantage point.
You already have the licence for the other frequency, you were using equipment to operate on it, and probably still have it somewhere? Why not get with the company that set up your existing system and see if it's something they can do for a reasonable amount of money with that existing equipment?
I agree, I think it's a bad idea for you to personally attempt to work on anything in the public service sector, any number of things can go wrong and mess the entire system up! But even on your own, you are looking at several thousands of dollars in equipment, even low power, to do it right. BUT, if you have existing gear, on an existing freq. I don't think it should cost all that much to get something usable set up for what you need.
Just another way to go about it? It sure wont hurt to discuss this with them and ask what is doable. Make sure you explain the problem fully, and make sure they understand the financial situation you are in! But I'd imagine you're community has done a lot of business with them and they would like to do more in the future!
Good luck!

I am actually under the impression that our Chief and LT do a lot of the radio stuff themselves. They program our radios themselves, they program our pages themselves, and generally don't like having radio stuff shipped out unless it's absolutely necessary (like the mutual aid radios for which we do not have 800 MHz system keys). But I'll ask them and see what they might have in store.

Public safety frequencies require frequency coordination and a license. This is a show-stopper. You will need to get the "concurrence" of the authority having jurisdiction (the licensee) to set ANYTHING that's not licensed up on the frequency pair they are using. Without that in writing, you will have spent your money on a license application that will go nowhere because it is opposed by one or more of the coordinators.

There are a number of different methods, but in order to proceed with any of them, please recall your project management coursework. First, you need to clearly define what your problem is - including the delimiters that go with it, then go about identifying the various methods you have at your disposal.

Since no two systems in public safety communications are alike, you will need to address the unique issues within your community and the system which serves it.

Some alternatives for consideration may include synchronous simulcast (it's probably the most seamless, but also the most expensive, as you need connectivity, a master clock that's usually referenced to a rubidium or cesium standard on each transmitter, and precise control of phasing launch), store-and-forward (which will be a nuisance and may hurt communication rather than help it), a low power auxiliary transmitter at your fire station activated by the communications center specifically for sending tones and voice announcements - these days that's fairly easy using two Telex Vega IP-223 modules back to back on a VPN, or some hybrid solution. Experimentation with intentional RF emitters may cause interference and will be an excursion from the FCC Rules.

Either way, you won't be able to pull a solution out of a dumpster... and if you do, you may cause harm. Remember, everything in public safety should be coordinated and licensed.

This is what I was afraid of. All of that sounds really, really expensive!

I guess I'll ask one last set of questions before I am willing to let this go into the unfeasible pile:

If all i'm doing is receiving on the public safety frequency, is there a band I can transmit on that I do not have to be licensed for? That is to say, if, for example, I were to receive on the public safety band, can I transmit on another band? It would be a bit basically like the more technologically savvy version of: taping the PTT down on a $10 walkie talkie and setting it next to our station plectron speakers, and then just having people carry $10 walkie talkies around on their belt with the volume turned up. Sure the range on it would be terrible, but I'd like to think I can get through about 4 walls with that set up!

Or, an analogous, but more high tech version. Receive on the public safety dispatch channel, and rebroadcast on "EMS Tac 2" (the tac channel that we are currently not using for anything). Since we control the license for this, is this more doable?

Finally, I just want to be sure that the following is what people are saying. No matter what, I'm not just going to be able to set up a solution that rebroadcasts on the same frequency as the dispatch channel now, no matter how low powered the signal is? Am I right on this? That is to say, we would have to reconfigure our pagers/radios to also be able to listen for a tone out on a different frequency regardless of whatever solution we come up with whether I do it myself or have a professional some in and we spend tens of thousands of dollars on it. Because we don't control the license for that frequency, there is no way we can repeat/signal boost on it?

Thanks for all the help guys!

 

[nd5y]

If all i'm doing is receiving on the public safety frequency, is there a band I can transmit on that I do not have to be licensed for? That is to say, if, for example, I were to receive on the public safety band, can I transmit on another band?

No. For what you want to do the FCC does not allow cross-service communications and there are no public safety frequencies that don't require a license for voice communications.

 

[KD0LWU]

No. For what you want to do the FCC does not allow cross-service communications and there are no public safety frequencies that don't require a license for voice communications.

And to add, to use the GMRS or FRS spectrum will not only be a violation of the FCC regulation, it will be placing you in a predicament for interference from "proper use" of these frequencies! Making the safety factor useless! It's a bad idea all the way around!
Yes, there are experimental sections of the FCC band plan, BUT, 1) They are not meant for repeater use, 2) you and everyone using any HAM frequencies will have to be licensed to operate in said freqs 3) to operate a repeater in the HAM band plan you still need to have a license to do so and the repeater will have to be figured into the band plan for the surrounding area 4) If, BIG if, you were granted a license to operate a safety service repeater inside the HAM band plan, you will NOT be looked upon fondly by most, if not all HAM operators as we are doing all we can to maintain our band plan as it is!

As for the LT and Chief setting things up themselves, this is not uncommon. But someone set them up with the equipment and taught them how to do this. Someone came in and installed the repeater system in the trucks, and built them, someone set up the tower and antenna at the station. This is who you need to talk to about what you are wanting to do! They can tell you what you can and can't do, the legalities of it and how to go forward with it, LEGALLY! This is what we are trying to impress upon you, you can do a lot of things in a lot of different ways, but none will be legal and if the FCC were to ever step in and see what was done, well, you just think your department is broke right now!

 

[WuLabsWuTecH]

Hi Guys,

Once again, thanks for all of the helpful information on this thread.

I looked into this more, and one of the guys asked why we don't just buy a couple of packs of the $10 walkie-talkies from walmart and when a run comes in, if someone is on station, he just uses those to call everyone else that's in a 1 block radius to come back. I came up with a cheaper solution--use the EMS Tac 2 channel that we are not using right now. The only time we use the EMS Tac 2 channel right now is when the stuff really hits the fan, and even then it's being used as a "car-to-car" channel (i.e. the tower is not in operation), so that should work.

Now, back to the licensing questions/technical questions. Is there a technological equivalent of taping down the PTT on a walkie set to EMS Tac 2 and placing it on a stand in front of the station PA/Plectron? And if so, is that something I can do myself?

I looked at our license, and it does list that frequency with our address as ours to use with a tower--the tower is just not operational at the moment...

If it's not something I can do myself, how much are we looking at to do this professionally? Would it be a wash of doing something like this versus trying to get a simulcast system set up?

Thanks guys!
-WU

 

[ofd8001]

As a fire chief I can understand your predicament.

Let me throw out another couple of thoughts. . .

I presume you've made your dispatch center aware of the situation and they have done some checking on their end, such as transmitter power, antenna feedlines and antenna. (The "getting worse lately" suggests to me that perhaps something on the dispatch center's end is degrading).

What we did around our place a few years ago was to set up a dedicated scanner on the dispatch frequency on an outside antenna. We then fed it into a computer that had a piece of software called "two tone detect". That recorded the dispatch audio and sent it to our members as either an e-mail or text message. There was a delay of perhaps a minute, but a delayed dispatch is better than no dispatch.

https://sites.google.com/site/radioetcetera/twotoneprogram

We have since began using a system called "I am Responding". While there is a charge for this service, it is rather modest. Instead of getting an audio recording as we did with two tone detect, we're now receving text dispatch messages.

IamResponding.com - Know Immediately who is responding to your dispatch as soon as the pagers go off!

There's another similar product called enotify I believe. Some other local fire departments use this.

The notion of "taping down" a portable on a channel isn't viable. I don't think the FCC would take too kindly to "dead carrier". Also the radio you would use for this may have a time-out timer which shuts of the transmitter after being keyed up for so long. Plus you've effectively killed that channel for any other use.

In short you may have some other options than to go through the bureaucratic hassles of getting licensing and the expenses of new hardware. Plus if you were to have a whole new frequency for immediate vicinity paging, that means the firefighters would need a second pager. Or if they have pagers capable of two frequency receive, they'll have to be sure they've selected the right frequency owing to where they are (unless you have the silent scan type pagers).

 

[brushfire21]

In my county we have had a few locations that are pager dead zones. these areas so happen to be near a few VFD's. The solution that was developed was pretty easy and inexpensive to install. A store and forward repeater was installed on the existing base radio/antenna. Whenever the tones for that particular station are activated, it pushes it out to those living within a few miles around the station. It was fairly inexpensive and very easy todo.

But as none of us are there, and we are conjecturing then other things may not be evident. But there is a solution, we may not have all the info.

 

[902]

I have some friends who are now using IamResponding and they say it works well for them.

Two way radios aren't made to be taped down and transmit continuously. Transmitting generates a great deal of heat and that isn't efficiently dissipated in a portable radio. Not to mention, most places do not have the frequency resources to consume.

Now, you did spark a synapse for something that's perfectly legal if you stay within the allowed parameters - a Part 15 device.

These are legal if you use them as instructed, AND, they can stay on continuously. Before I moved, I was "rebroadcasting" an over-the-Internet signal so I could listen to it in my yard on an AM/FM radio. It worked fine. I wouldn't be comfortable having that as primary fill-in coverage, though.

Another caveat - it's easy to get into trouble using higher power and bigger antenna gain than allowed if you do this.

 

[WB4CS]

Not to sound like a broken record, but why not contact a local commercial radio shop and get an estimate on pricing for what you want to do?

Again, kudos on wanting to find a solution on your own. However, when dealing with public safety, this radio system needs to be dependable since that response time and peoples lives are dependent on this system. Taping a PTT open or rigging an AM/FM rebroadcast of the system is neither professional nor dependable.

I understand your desire to fix this cheaply and on your own, but no matter how many times you ask the question the best answer isn't going to change. Imagine if this jury rigged system fails and a call doesn't get out and someone dies as a result? Imagine if you rig up something that works but causes interference to another radio service or user and the FCC investigates, do you know how much money an FCC fine is? It ain't cheap!