How do you think this system works??

[kb0nly]

Ever since our county upgraded there has been some debate over how it actually functions, we lost our contacts due to retirements and so we don't have an inside man anymore. Some may say i should have posted this in the MN specific forum but its not really a location specific question, it's more of a functional/operational question.

Here is what we know of the system in Lincoln County Minnesota, this was gathered from the FCC ULS database and the info on the RR Database, but its not all labeled correctly on there and it doesn't really help to explain the operation.

A little background.. Ivanhoe is the county seat, the courthouse and law enforcement center are located there, hence the dispatch center is there as well. I omitted the frequencies such as MIMS and MINSEF which are statewide, also statewide EMS and Fire, etc.. All we are concerned with here is the new P25 digital system used by the local PD and County Sheriff. Each city has its own PD and units, so thats why each have their own tower location i'm guessing, but there is some other questions. I will fill them in...

Ivanhoe

154.875 (100W) .3 MI North on Tower
458.600 TX (5W FXO) / 453.600 RX County Courthouse
458.900 TX (5W FXO) / 453.900 RX County Courthouse
465.100 TX (5W FXO) / 460.100 RX County Courthouse

The Ivanhoe location seems pretty self explanatory, the main dispatch is on 154.875, this is the main frequency on which you hear dispatch. The UHF frequencies are the opposite of the other cities and appear to be some kind of UHF backbone between the sites. Listening on the UHF frequencies its just data, not P25 as the VHF side is, the data sound doesn't change when the VHF side is active, so i don't know what kind of data this is, someone chime in if they know what the UHF side is actually.

Hendricks

155.415 (100W) TX Water Tower
453.600 TX (5W FXO) / 458.600 RX Water Tower

The Hendricks location has a VHF transmitter, and i assume it has to have a VHF receiver (readon for explanation below). They are farther away in distance and have some geographic problems to overcome to the main dispatch, so they needed their own VHF frequency. Also at this site is a UHF repeater. And again its just a continuous stream of data.


Tyler

453.900 TX (5W FXO) / 458.900 RX Water Tower

The Tyler location is a bit different in that it doesn't have its own VHF transmit. I live in Tyler, and the main dispatch on 154.875 is full scale on a HT here due to being closer than the other cities to Ivanhoe and without anything in the way geographically. So they just didn't need a seperate transmit from what i can tell (more on that below).

Lake Benton

155.730 TX (100W) 1.5 Miles North and 1.5 Miles West - East River Electric Tower
460.100 TX (5W FXO) / 465.100 RX 1.5 Miles North and 1.5 Miles West - East River Electric Tower

The Lake Benton location seems to be the same as the Hendricks location. There is a new VHF transmit frequency and the receive must be one of the same frequencies already in use. There is a UHF repeater in operation here as well. Lake Benton is down in a hole, the whole town is in a large valley and the main dispatch doesn't get down in there very well, reason they get their own transmit i assume.

Ok, so here is how I THINK it works...

All the mobiles are licensed for TX at 100w on:

154.875 - Talkaround of the main dispatch
156.090 - Dispatch Receive, also used to be the countywide repeater input when they were analog
155.475 - Which is statewide MINSEF.

So my guess is that each of the tower sites has an input of 156.090 and this is a Voter system?

Each site has its own VHF transmit except Tyler (will get to that in a moment) so that each PD sits on their own channel. However, when the transmit they are heard on all three VHF transmit frequencies so everyone can hear each other. The Sheriff's department seems to move around as they get to different parts of the county, switching between towers, for the best receive.

Tyler doesn't have its own VHF Transmit because we are closer to Ivanhoe than the rest and can make use of the 154.875 transmit from dispatch in Ivanhoe instead, so it would appear we only have a Voter receiver on 156.090, most likely to give better handheld coverage since we have the county fairgrounds here and they used to have coverage problems there.

Does this make sense? Am i seeing this wrong??

 

[tbiggums]

It sounds like a voted system to me. It appears they're using UHF links as opposed to leased lines or microwave. The continuous data on UHF is probably the Astro modems in the Quantar repeaters and Astro-TAC receivers linking to the Astro-TAC comparator. These would run 9600 bps data continuously, and the sound wouldn't change when someone is talking on VHF.

There would have to be a single VHF input frequency, but there could be multiple VHF output frequencies.

Even if a site has only a VHF receiver at it, it would still need a full-duplex link (UHF or otherwise) back to the comparator site.

They probably have directional UHF antennas at the outlying sites, all pointing back to the central location (Ivanhoe)?

 

[DickH]

... Some may say i should have posted this in the MN specific forum but its not really a location specific question, it's more of a functional/operational question.

I think it's very specific to that system and the MN people may know exactly how it works.

 

[kb0nly]

It sounds like a voted system to me. It appears they're using UHF links as opposed to leased lines or microwave. The continuous data on UHF is probably the Astro modems in the Quantar repeaters and Astro-TAC receivers linking to the Astro-TAC comparator. These would run 9600 bps data continuously, and the sound wouldn't change when someone is talking on VHF.

There would have to be a single VHF input frequency, but there could be multiple VHF output frequencies.

Even if a site has only a VHF receiver at it, it would still need a full-duplex link (UHF or otherwise) back to the comparator site.

They probably have directional UHF antennas at the outlying sites, all pointing back to the central location (Ivanhoe)?

I think your dead on! The fact that they run continuous data and doesn't change with activity seems to be the giveaway as to what they are using. I was doing some research on the voter systems and how they are constructed with some time off for the holiday.

And yes, they have small yagi's on each site pointed towards Ivanhoe as its the central location. Even the FCC licenses for these sites show that they have a directional antenna. I drove past the water tower here in Tyler, its just three blocks down the street from me, and there is a 6el yagi on the water tower pointed towards Ivanhoe, and a large VHF base antenna for the voter receiver. When i get time i plan on driving over and looking at the other sites but i'm sure they are similar.

 

[kb0nly]

I think it's very specific to that system and the MN people may know exactly how it works.

If its not Twin Cities it doesn't seem to be discussed much on here. We are out in the boonies by comparison!! LOL

 

[blueangel-eric]

i wonder if Miami CO KS is on a voter system because they have tons of SO frequencies all over the county. I've not been there enough to notice what the system is. and when i'm there i'm too busy watching trains, and listening to the railroad on the radio, to pay attention.

I know about the data UHF link you guys talk about cause that's what the Emporia PD and or Lyon CO SO uses to link the base to the towers. sometimes i've had that data noise interfere on other UHF freqs in the path of the signal with in a few blocks from the station. the noise is constant. i call it the fire engine sound because it sounds like a fire engine horn stuck on.

 

[DickH]

If its not Twin Cities it doesn't seem to be discussed much on here. We are out in the boonies by comparison!! LOL

Why would you make such a rash statement when you haven't even asked on the MN Forum?

 

[kb0nly]

Why would you make such a rash statement when you haven't even asked on the MN Forum?

Because other posts of mine in the MN forum have gone unnoticed. Let's say i know by experience.

Most of the MN forums active readers/posters don't know anything about these far reaching outlying parts of the state.

 

[coldbricks]

This is a wicked thread. I never even knew people do this. What is the advantage of UHF vs microwave in the link situation? $? It doesnt sound like it would be cheaper!

 

[tbiggums]

It could be that the paths between the outlying sites and the central site are not well suited to microwave links. They may be somewhat obstructed by terrain where several watts on UHF with good antennas will still make it through. Also, with the exception of real short hops, the microwave antennas are usually much larger than a UHF yagi, so maybe they would have needed stronger towers at the sites to hold microwave antennas.

Good microwave radios are unlikely to be cheaper than a UHF Quantar station, as well.

What UHF antenna arrangement are they using at Ivanhoe? Do they have a UHF yagi aimed at each outlying site? Or maybe they're using a combiner/multi-coupler to a couple of omni UHF antennas...

 

[smokeyjones666]

Because other posts of mine in the MN forum have gone unnoticed. Let's say i know by experience.

Most of the MN forums active readers/posters don't know anything about these far reaching outlying parts of the state.

I'm rather glad you started this thread, I live in the TC but I agree there's not much being shared about areas outside of the metro. I find the system facinating and I like to learn as much as I can for my occasional trips outside of the metro area.

 

[kb0nly]

I think the biggest issue here was cost, UHF versus Microwave is like comparing pennies to dollars, at least when it comes to the support structure and equipment. There really isn't a terrain obstruction problem between these sites, again it just comes down to dollars. Also a while back an internet provider wanted to put a dish on the water tower here in Tyler, they were denied, the city engineer said that the structure could not reliably support it. Whereas the yagi is just clamped onto one of the rails of the catwalks going around the tank.

The other benefit is that by going UHF they were able to use existing structures that can support the simple yagi antenna's that they used. If i get a chance in the next couple days i will snap some photos of the antenna's on the water tower here in Tyler. Basically just a uhf yagi for the backbone and a vhf vertical for the voter receiver.

I haven't been to Ivanhoe recently, but i don't recall any yagi's on the tower. I know there is two verticals near the top, i would guess by their differences in length that one is VHF and the other is UHF. If you look at the FCC ULS license listings you will see the UHF license for Tyler, Lake Benton, Hendricks, all show an antenna gain of 10db, whereas the Ivanhoe UHF license doesn't show the gain figure. Its been my experience in trolling the FCC ULS database, to identify frequencies i have found, that the vertical omnidirectional antenna gains aren't generally listed, at least it seems for licenses around here. But every time a yagi comes into play they list the gain.

I will have to look it over again the next time i get up there. But i would guess its just a vertical omni in Ivanhoe and the outlying sites have yagi's pointed towards Ivanhoe.

 

[kb0nly]

I'm rather glad you started this thread, I live in the TC but I agree there's not much being shared about areas outside of the metro. I find the system facinating and I like to learn as much as I can for my occasional trips outside of the metro area.

I find it fascinating reading about the systems in use in the TC area. Some day that ARMER system will work its way out here. Looking at the plans for it they show the tower sites and the microwave links on a large map of the state, really intriguing. Looks like they will re-use a few of the sites when this area goes ARMER, just replacing the equipment, and antennas of course, at each site.

 

[kb0nly]

While on the subject of ARMER, not to wander away from the current subject, Smokey do you know if Pine County MN is on the ARMER system yet?? I got a friend up there that is a deputy for the sheriff's department.

I see all the analog VHF stuff is still listed for Pine County on the RR database.

 

[DickH]

... Looks like they will re-use a few of the sites when this area goes ARMER, just replacing the equipment, and antennas of course, at each site.

If it's like other large trunked systems, "just" replacing the equipment and antennas is likely "just" the beginning. Those systems usually have a monthly charge for each mobile and portable and it will likely end up costing a whole lot more than maintaining your existing VHF/UHF system.

 

[kb0nly]

If it's like other large trunked systems, "just" replacing the equipment and antennas is likely "just" the beginning. Those systems usually have a monthly charge for each mobile and portable and it will likely end up costing a whole lot more than maintaining your existing VHF/UHF system.

Its not like other systems though, thats not how this one is being deployed. Each county and every entity in each county gets to choose if they want to be on ARMER, if so they buy the radio gear and the state gives them a talkgroup, done. Each county is responsible for its own equipment and the state is responsible for the system operation.

 

[Russell]

Its not like other systems though, thats not how this one is being deployed. Each county and every entity in each county gets to choose if they want to be on ARMER, if so they buy the radio gear and the state gives them a talkgroup, done. Each county is responsible for its own equipment and the state is responsible for the system operation.

P25 systems have monthly "user" fees or "licensing" fees. These fees are usually paid by the end users not the system operators. We have some counties in Texas where departments are refusing to "join" such systems because they can't afford or don't want to pay the monthly user fees. It's hard to go from outright owning your system to paying monthly fees.

 

[n5ims]

P25 systems have monthly "user" fees or "licensing" fees. These fees are usually paid by the end users not the system operators. We have some counties in Texas where departments are refusing to "join" such systems because they can't afford or don't want to pay the monthly user fees. It's hard to go from outright owning your system to paying monthly fees.

For the agencies, it's actually "cheaper" to spend $20 million on a new system than to spend $5,000 a month on fees, as stupid as that sounds. The $20 million is a "capital project" and doesn't affect the agency's budget at all (and often comes from a grant, funds from a local bond election, or a combination of the two). The $5,000 is an ongoing expense and must be paid for out of the agency's budget money where something else probably must get cut out to make room for it.

Look at it from the chief's view, "We can have our own multi-million dollar system that we own and control that won't cost my agency a dime or we can join that system where we have no control and to pay for it we'll have to move to a 3 year car replacement cycle from the current 2 year cycle."

 

[kb0nly]

There is no monthly fees here, this is a statewide and state funded system. All the operating costs come from the existing budgets, such as power to the sites, maintenance contracts, etc.

The two towers in my county only one is new construction because the existing one next to it was leased and too short to provide the coverage needed. So a new site is being built on a state grant. The other site is an existing site that is merely getting a remodeling, new feedline, new antennas, microwave dishes, and all the related equipment, in place of the current equipment on VHF. The site doesn't change much otherwise, they will drop in a new pre-made building, put all the antennas on the tower, and a new generator capable of running the entire site. On to the next...

Most of the ARMER sites are actually existing MNDOT tower sites, used to provided statewide VHF coverage for MNDOT operations. MNDOT actually paved the way, no pun intended, in that they are the largest user of the new system and most of the ARMER sites are on existing MNDOT towers.

I have the full budget, integration plan, and a spreadsheet showing the construction costs, along with mention of the ongoing cost of utilities and maintenance that they have always paid for with the existing sites.

On top of that is the cost to buy the new radios. I have all those numbers as well.

This is NOT a subscriber based system, there is NOT a monthly access charge or fee. Its all state funded and built. That's what i am trying to say in previous posts, this is not a system built by Joe Radio to be used by Joe Public or Johnny Law, this is a dedicated system owned and operated by the State of MN.

Any Public Service entities can get on it, all they have to do is buy radios basically. Yes there is more to it than that, applying and getting granted access and such, but they aren't paying a monthly fee because each county absorbs it as their normal operating cost just like they did with their VHF system.

 

[cifn2]

It sounds like a voted system to me. It appears they're using UHF links as opposed to leased lines or microwave. The continuous data on UHF is probably the Astro modems in the Quantar repeaters and Astro-TAC receivers linking to the Astro-TAC comparator. These would run 9600 bps data continuously, and the sound wouldn't change when someone is talking on VHF.

There would have to be a single VHF input frequency, but there could be multiple VHF output frequencies.

Even if a site has only a VHF receiver at it, it would still need a full-duplex link (UHF or otherwise) back to the comparator site.

They probably have directional UHF antennas at the outlying sites, all pointing back to the central location (Ivanhoe)?

I agree about the voting system, have seen this before, look up the wiki page on Wayne County,IL . Its a rural county with 2-3 towers on the 400mhz range, and primary comms on the 150 mhz area.