Repeater Reference?

[jsmith42]

We live on an island that's 9 miles long but the topography prevents line-of-site to/from all neighborhoods. Our FD Mobiles can usually punch through to Dispatch but portables can't make it, so we're exploring the addition of repeaters. My calculations say that we'll need two, one at the north end of the island and one in the south end.

I've set up single repeater but don't enough about setting up multiples. Does anyone know resources that I tap for knowledge, or can anyone sum up the concepts in a concise answer?

 

[rfradioconsult]

The best solution given the very basic info you have given would be a single repeater located near the middle of your coverage area, with two voting receiver locations at either end of the island tied into a voting comparer located at the repeater location. This is how it should be done, clean and would provide the coverage you desire. You need to find a communications professional to guide you through the process.

 

[jsmith42]

Perfect answer, just what I was looking for. I’m FCC ticketed and experience with single repeaters, both amateur and commercial, but haven’t had the need for multi-site.

There are ‘professionals’ in the mix that disagree on the best solution, e.g., voting receivers, multiple independent repeaters (huh?), rules to follow about when/where to use what, and other more complicated schemes. We’d eventually engage one of them for the actual implementation, but I’m looking for a reality check. What you describe is exactly what I suspected.

A few questions…
> What is communication link is used between remote receivers and the repeater?
> Are our 2 dispatch centers simply base stations with separate Tx/Rx freq, or do they link to the repeater?
> With all of the new FCC regs, e.g, 12.5mHz bandwidth, is there a new standard Tx/Rx offset?
> Does anyone know of a reference – web or print – for repeater design/build?

 

[prcguy]

With only 9 miles of coverage needed I would think a high performance repeater and antenna somewhere in the middle would provide coverage even with rough terrain, it would be less than 5mi omni.
prcguy

 

[mmckenna]

A few questions…
> What is communication link is used between remote receivers and the repeater?

2 wire or 4 wire telco circuits are probably the most popular, and in your case, the most appropriate. Others are microwave, fiber optic, IP (yetch!), or a separate radio link. Remember that you'll have 3 receivers, one at each end of the island, or whatever design is chosen, and the receiver at the repeater. You'll want to run those three through a voter and it will pick the best signal to send to the transmitter. If you can't cover an island that size with 3 receivers, you've got some serious design issues. By the way, how tall is the tower your current repeater is on?

> Are our 2 dispatch centers simply base stations with separate Tx/Rx freq, or do they link to the repeater?

Ideally, both. The voter will allow connection to the console. You can set up a couple of handy features if your voter supports it:
Mobiles/portables can over ride the dispatcher, good for officer safety.
voted receiver display, you can set up a display that will show which receiver is being used. Good for trouble shooting. You can also set up a "switch" that would allow dispatchers to remotely disable a receiver. Good if one fails, telco line gets noisy, localized interference, etc.

Dispatch should have a back up radio or 2 just in case.

> With all of the new FCC regs, e.g, 12.5mHz bandwidth, is there a new standard Tx/Rx offset?

Nothing changed in that respect. UHF is often 5MHz off set. No standard offset for VHF.

> Does anyone know of a reference – web or print – for repeater design/build?

Get thee to a radio shop that has done this before. It isn't something that you DIY. Setting up the 2 wire circuits from the remote receivers involves adjusting for circuit loss, this requires a TIMS set or similar device. If you haven't set up voters before, it's not impossible, but you'll retain your sanity if you get help. Also, for public safety, you really need to have a competent person involved that has done these systems. It isn't something that you put together with parts off e-bay, it requires some design skills that most ham operators don't have. Don't get offended by this, but based on the questions you are asking, you likely don't have the skills/knowledge to do this on your own. If fire and police officers are relying on this system, it needs to be done right.

 

[rfradioconsult]

You have received some very sound advice, this isn't a scavenger hunt but needs to be handled by a professional, the best advice is seek out a professional and heed what he feels would be the best solution.

 

[ecps92]

Have you talked to the PD to see how they like the RISCON network that is available for Statewide coverage ?? ?? That is an option to

We live on an island that's 9 miles long but the topography prevents line-of-site to/from all neighborhoods. Our FD Mobiles can usually punch through to Dispatch but portables can't make it, so we're exploring the addition of repeaters. My calculations say that we'll need two, one at the north end of the island and one in the south end.

I've set up single repeater but don't enough about setting up multiples. Does anyone know resources that I tap for knowledge, or can anyone sum up the concepts in a concise answer?

 

[W2NJS]

You might also consider getting a coverage map of your present system which would show signal coverage in the various coverage areas now being used. From that a professional estimator could make up a plan that works and, just as important, guarantee that whatever is proposed will definitely work and meet your needs.

 

[jeatock]

You might also consider getting a coverage map of your present system which would show signal coverage in the various coverage areas now being used. From that a professional estimator could make up a plan that works and, just as important, guarantee that whatever is proposed will definitely work and meet your needs.

I second that. Radio propagation software (and someone who knows how to use it) can give you a good guess without having to invest in equipment trial and error. Then remember that radio is 1/3 science, 1/3 magic and 1/3 dumb luck.

The simplest system would have a single base transmitter with universal portable downlink coverage, and remote voting receivers to make portable uplink coverage universal. Where and how many can be determined via propagation software. Backhaul between the voting receivers and the central site can be microwave (not as expensive as it sounds), or uplink translation to UHF or 7/800.

I would avoid public utility backhaul for "matter of life and death" public safety communications- you have little control over outages and "issues", and if it hits the fan they may not be there at all.

Voting can be done quite nicely on analog systems- don't let anyone tell you otherwise. I'm a big fan of the JPS/Raytheon SNV equipment.

 

[rapidcharger]

If the FD in question is the one located in the town that your location specifies on the forum, the ULS says your antenna is only about 54 feet. Is that where dispatch is located? If so, that's not even clearing the tree tops.

 

[jsmith42]

Catching up here... My quest for knowledge is because I'm not up to speed and -- more importantly -- because several 'professionals' disagree. Rest assured that this won't be DIY but want to have a solid footing of the matter before making any recommendations.

Using USGS topo maps and field survey I created a contour of the coverage area and used a spectrum analyzer to map ROM signal strength at key locations. We've also performed numerous real-life tests with mobile and portable radios. Naturally, narrowbanding didn't help.

This is my first foray into the forums and I've gotten a wealth of info which pointed me to more research. It looks like I'll recommend two voting receivers, one on the existing tower and one on a repeater tower at a higher elevation. For the link we have several options available: stand-alone microwave, town WAN, or spare 100mil FA pairs. A mobile uplink on the pumpers might also help on fireground, though that might not be necessary.

 

[mmckenna]

OK, rather than adding a second receiver to the main site, why not just move your antenna up the tower? The new coaxial cable alone might help if the existing stuff has been up there more than 10 years or so, and getting the antenna up higher, and hopefully with better cable, might address the issue on it's own, or may make it that you only have to add one more receiver.
A decent receiver is going to cost you some bucks, the voter won't be cheap, all the support stuff, coax, connectors, battery back up, etc, will add up pretty quick.

 

[jsmith42]

Primary Tx antenna is already at the top of the tower and uses semi-rigid. Current tower location is toward the southern end of the island and will never Rx portables from the other side of the 'hump' in the middle of the island or even mobiles in the north end. A repeater with Rx #1 on the 'hump' is the best bet, with Rx #2 on the existing tower to solve other topo issues.

 

[rapidcharger]

But your current antenna is only at 54', is it not?
Google street view confirms it.

You're putting the cart before the horse.
Why don't you run the numbers with a 150' antenna located in the center of the island.
It's not going to give you 100% body worn portable coverage but it's a simpler, more affordable way drastically improve the situation.

 

[jsmith42]

Top of tower is actually 85', antenna extends 15ft up from there. Geography says that a tower at that location would need to be 200ft to be effective, and still probably won't Rx portables. Testing with mobile radios (at ground level) and a meter say best results would be from 2 receivers, though a single Tx tower would suffice.

 

[jsmith42]

missed this - "Radio propagation software (and someone who knows how to use it) can give you a good guess without having to invest in equipment trial and error. Then remember that radio is 1/3 science, 1/3 magic and 1/3 dumb luck."

I do know how to use it, but geography, foliage/season, and structures such as water tanks can make the best software useless. My best results come from using a spectrum analyzer (one that lets you measure secondary reception, harmonics, etc) and real-life tests. That said, I disagree with the formula... less science, more magic and dumb luck.

 

[Alarms50]

Another alternative that has not been touched on here are mobile repeaters. Depending on how, and when, the portables are to be used, this might be an option. If the portables are only used during fire emergencies (or when you are out with the rigs), mounting the repeater on the rig (or Chief's car(s)) might be the choice for you.

 

[jsmith42]

Thanks for that. I mentioned mobile uplinks on the pumpers earlier in the thread. That would help the portables on fireground when in our worst-case locations or when they're inside some structures.

 

[mmckenna]

Mobile repeaters or "extenders" can get expensive if you are trying to do it in band (VHF to VHF) Not impossible, but it takes some work. You'd need a new VHF frequency pretty far away from all your existing stuff.

It might be cheaper, but again, it isn't a plug and play solution. You'd need a good Pyramid dealer to do the set up and install.

It would be pretty flexible and would work even if on a mutual aid response outside your area.

 

[jeatock]

(Snicker) But if we claim less than "1/3 science" nobody would hire consultants.