Ok, before I'm declared insane, I have an idea and want to run it past everyone, see if it's been tried before....
Planning a repeater system with remote receivers. Transmit will be located in center of county with an MSR2000 VHF. Remote Receivers to be installed in 4 locations (North, South, East, and West).
Here is the thought for the remote receievers, take a VHF Maxtrac (or equivilent) and interface to a UHF Maxtrac on a yagi pointed to the main transmit site. Each remote setup will be locked in a cabinet and inside a secure building.
As for the setup at the main site, have a UHF receive antenna up high enough to hear all the remote's, then bring it down, tie it into 4 UHF Maxtracs for receivers (with appropriate splitting and protection, etc.) and plug each UHF Maxtrac into a 5 position voter. The voter should pick the best signal and provide it to the MSR2000 if we interface it correctly.
As far as for the master transmit site, we have access to a very good location with lots of room, so that is not an issue.
For the remote sites, we are looking at fire stations in each of the four areas, due to security and access issues. We are also looking at having our electric co-op place a 50ft wooden utility pole at each site for the VHF and UHF Antennas, as this would be done at no cost for us.
So here is what I'm looking at, for each remote site would be 1 VHF Maxtrac, 1 UHF Maxtrac, Interface between the two, VHF Omni Antenna for top of pole, UHF Yagi antenna, Power Supply, Locking Cabinet, Lightning Protection, Coax.
For the master site, the VHF MSR2000, Voter, 4 UHF Maxtracs for rx from remotes, UHF Omni Antenna, VHF DB-224 antenna, Hardline, connectors, lightning and power protection, locking cabinet.
Also licensing for the VHF RX and TX freqs, and for 4 UHF freqs.
The whole goal on this is to create a countywide system for nearly 100% portable coverage.
Anybody tried anything similar to this or have any insight, or just want to call me generally stupid?
Thanks!
Idea for Countywide Repeater System...
Moderator: Queue Moderator
WARNING - RED FLAG WAVING - Voting systems are a LOT of work!
OK, now that you've been warned. Yes, a voting system can do wonders for portable coverage. You do have the right idea, a centrally located main transmitter and one or more remote receivers appropriately located for portable talk in.
As you can see, your four remote receivers each comprise a cross-band repeater. Collectively, that means what appears as a single repeater to your users is actually more work to set up and maintain then FIVE individual repeaters.
Now, as far as equipment goes, your selection of maxtracs for the remote receivers will complicate your life. Real voting receivers are preferable. Companies like Motorola and GE have done this for years. The principle difference is the use of a status tone sent to the comparator from the remote receiver. This provides for real time system AGC and real time unsquelch indication. Without that, you will have serious issues with level setting, audio quality differences as the system switches sites, audio holes, etc.
Unfortunately, these status tone systems are really happiest with leased lines or microwave circuits to the remote sites. The status tone is continuous which creates problems for RF linked sites.
It has been done with continuous keyed links which removes one issue. RF links also have the disadvantage of passing your incoming signal through two audio limiter / roll-off circuits. This makes it very hard to match the remote site audio to the local [co-located with the voter] site.
Some folks set up the remote receive sites as cross band repeaters [as you have suggested] Then they use regular voting type receivers [with status tone] at the comparator / transmitter site. That will work, but has the above mentioned level setting and audio holes issues.
You best bet is to find someone local with voting system experience to advise and assist with the project.
OK, now that you've been warned. Yes, a voting system can do wonders for portable coverage. You do have the right idea, a centrally located main transmitter and one or more remote receivers appropriately located for portable talk in.
As you can see, your four remote receivers each comprise a cross-band repeater. Collectively, that means what appears as a single repeater to your users is actually more work to set up and maintain then FIVE individual repeaters.
Now, as far as equipment goes, your selection of maxtracs for the remote receivers will complicate your life. Real voting receivers are preferable. Companies like Motorola and GE have done this for years. The principle difference is the use of a status tone sent to the comparator from the remote receiver. This provides for real time system AGC and real time unsquelch indication. Without that, you will have serious issues with level setting, audio quality differences as the system switches sites, audio holes, etc.
Unfortunately, these status tone systems are really happiest with leased lines or microwave circuits to the remote sites. The status tone is continuous which creates problems for RF linked sites.
It has been done with continuous keyed links which removes one issue. RF links also have the disadvantage of passing your incoming signal through two audio limiter / roll-off circuits. This makes it very hard to match the remote site audio to the local [co-located with the voter] site.
Some folks set up the remote receive sites as cross band repeaters [as you have suggested] Then they use regular voting type receivers [with status tone] at the comparator / transmitter site. That will work, but has the above mentioned level setting and audio holes issues.
You best bet is to find someone local with voting system experience to advise and assist with the project.
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apco25
- Posts: 2685
- Joined: Tue Oct 30, 2001 4:00 pm
- What radios do you own?: APX / Astro 25 / Harris
RF linking is done all the time including voted system.
First though a few questions
What is the topography of the county you're working with?
Flat, hills / valleys, mountains? That will make a big difference in your coverage needs.
100% coverage for what? Mobiles? Portables? Both? 100% mobile coverage does not equate to 100% portable coverage.
Have you done a signal propagation test or better yet computer Rf modeling of the proposed system?
50ft poles may not be enough to accomplish what you need. Where did you come up with that heigh figure?
Do you have a clear RF path for the link frequencies?
First though a few questions
What is the topography of the county you're working with?
Flat, hills / valleys, mountains? That will make a big difference in your coverage needs.
100% coverage for what? Mobiles? Portables? Both? 100% mobile coverage does not equate to 100% portable coverage.
Have you done a signal propagation test or better yet computer Rf modeling of the proposed system?
50ft poles may not be enough to accomplish what you need. Where did you come up with that heigh figure?
Do you have a clear RF path for the link frequencies?
"Some men just don't know their limitations"
I know of many systems that work just like that. It is very doable and doesn't make you loony. However, to make the system fully supervised so you will know if a site is down is a little more complicated. Lets look at the two ways of doing this....
Easiest way:
Each of your remote sites receive the UHF portable, key up the VHF link and send the signal to the VHF receiver at the main site. The VHF link receiver receives the transmission and a COR logic pin on the receiver tells the voter the site is receiving. Once you get past setting the audio levels, it would work very well. The problem is, if one of your receiver sites craps out, you have no way of knowing until your portables don't seem to work anymore.
More complicated:
Exact same thing as above except your links are always transmitting. When the UHF recievers are not recieving anything, there is a 1950hz "status tone" being sent over the link. The voter sees this status tone and says "Oh good, the link is on and working and I can use that tone to set audio levels!" When the UHF reciever starts receiving your portables, the status tone stops and your audio takes it's place. The voter sees the absense of status tone and assumes that means there is a signal to start voting on. If for example, your link craps out or the antenna get knocked over by a plane, the status tone would also go away. If the voter hears no status tone and no audio at all, it assumes this means there is a link malfunction and fails the site. This will give you a fail indication both at the site and however else you want to indicate site alarms.
Basicly, it comes down to un-supervised remote sites vs supervised remote sites.
Many ham radio repeaters use the unsupervised system since it is not a "critical" system and is a whole lot cheaper. To make the supervised status tone system, you need link transmitters that are reliable enough for continuous duty as they need to transmit 24/7. A public safety system really SHOULD be the latter. The other option is leased telco pairs from the phone company. That works the same way as the supervised link, just over he phone lines instead of the airwaves. You don't need more radios and antennas but you also have to live with phone company screw ups and cars taking out phone lines. If you happen to be in an area served by SBC, you may also want to look into a good blood pressure medication.
But, in the end, it comes to what you can afford. To be honest, anythign is better than nothing. If you can't afford the best but you have nothing now, anything is an improvement.
Easiest way:
Each of your remote sites receive the UHF portable, key up the VHF link and send the signal to the VHF receiver at the main site. The VHF link receiver receives the transmission and a COR logic pin on the receiver tells the voter the site is receiving. Once you get past setting the audio levels, it would work very well. The problem is, if one of your receiver sites craps out, you have no way of knowing until your portables don't seem to work anymore.
More complicated:
Exact same thing as above except your links are always transmitting. When the UHF recievers are not recieving anything, there is a 1950hz "status tone" being sent over the link. The voter sees this status tone and says "Oh good, the link is on and working and I can use that tone to set audio levels!" When the UHF reciever starts receiving your portables, the status tone stops and your audio takes it's place. The voter sees the absense of status tone and assumes that means there is a signal to start voting on. If for example, your link craps out or the antenna get knocked over by a plane, the status tone would also go away. If the voter hears no status tone and no audio at all, it assumes this means there is a link malfunction and fails the site. This will give you a fail indication both at the site and however else you want to indicate site alarms.
Basicly, it comes down to un-supervised remote sites vs supervised remote sites.
Many ham radio repeaters use the unsupervised system since it is not a "critical" system and is a whole lot cheaper. To make the supervised status tone system, you need link transmitters that are reliable enough for continuous duty as they need to transmit 24/7. A public safety system really SHOULD be the latter. The other option is leased telco pairs from the phone company. That works the same way as the supervised link, just over he phone lines instead of the airwaves. You don't need more radios and antennas but you also have to live with phone company screw ups and cars taking out phone lines. If you happen to be in an area served by SBC, you may also want to look into a good blood pressure medication.
But, in the end, it comes to what you can afford. To be honest, anythign is better than nothing. If you can't afford the best but you have nothing now, anything is an improvement.
"I'll eat you like a plate of bacon and eggs in the morning. "
- Some loser on rr.com
eBay at it's finest:
Me: "What exactly is a 900Mhz UHF CB?"
Them: "A very nice CB at 900Mhz speed!"
- Some loser on rr.com
eBay at it's finest:
Me: "What exactly is a 900Mhz UHF CB?"
Them: "A very nice CB at 900Mhz speed!"
Jon,
I think you are only partially insane. Try this, pick two sites in the county. Construct the appropriate apparatus and use two VHF MSR2000s. They are built for continuous duty and should offer you decent portable coverage and good mobile coverage.
Put one site out in the boonies where the hoot-owls rape the chickens and the other at the opposite end. Cost less to do then acquiring all of the necessary equipment for your idea, as well as less than the cost of the co-pays to monitor serious blood pressure conditions.
My .02.
I think you are only partially insane. Try this, pick two sites in the county. Construct the appropriate apparatus and use two VHF MSR2000s. They are built for continuous duty and should offer you decent portable coverage and good mobile coverage.
Put one site out in the boonies where the hoot-owls rape the chickens and the other at the opposite end. Cost less to do then acquiring all of the necessary equipment for your idea, as well as less than the cost of the co-pays to monitor serious blood pressure conditions.
My .02.
Ok, to answer a few of the questions... The area that this will be done in is Laclede County, in and around the city of Lebanon. The goal is to provide nearly 100 % portable coverage. The estimates on pole height so far are just that, estimates. Have not done any propogation studies as of yet for that. The territory is hilly, and in some places it's billy goat country / straight up and down (welcome to the Ozarks). Where the stations are located, they are realtively high, will not have a problem with UHF Line of Sight.
Any other questions / ideas?
Any other questions / ideas?
My county is dealing with a similar issue. They have set a long range plan to eventually have an all UHF voting repeater system. We currently use a Lowband/UHF analog conventional system. Each department has their own mix of this system. Some are already on all UHF, some are a mix like my department and some are all Lowband. Our county is located in eastern Connecticut. We have one central dispatch center. They currently do not own and operate all of the radio equipment in our county. This is the firs big problem. Second is the big disparity in financial resources available to the various departments. The all UHF departments have significant monies to upgrade thier radio equipment. The third major issue is topography. The department on all UHF is a small town in sq. mi. and realtively flat. My town is both large (for our state) and very rough terrain. Thus why we still use UHF/Lowband. In areas where our UHF cannot hit our tower we use our vehicular cross band repeaters and TX on Lowband. Departmenst still using all Lowband cannot afford to install cross band repeater systems.
If you are going to use a voting repeater system in your area you must make sure that you have sufficient coverage otherwise you will be plauged by dead spots. Also when I talked to some other agencies that went to a voting repeater system they had the following issues. Of the agencies that used RF to link their sites initially, all of them swithced to either Microwave or hardline. The voters apparently had significant problems recieving the signals from the remote sites and could not properly isolate the strongest RX signal. This resulted in significant audio quality problems. The two problems with switching are; Microwave is expensive up front cost. Leasing hardlines form the phone company are expensive long term cost.
Our town which operates its own police department and dispatch center has looked into using cell tower as sites for a town only voting repeater system. Even with free space the up front hardware costs for this system are huge. Initial estimates are close to $750,000. Pricing was based on budgetary quotes on Daniels Electronic System and Tait radios. These are high end radios designed for this type of service. We are looking at 5 sites within our 38 sq. mi. town. This study also assumed that the towers we were looking at would give us adequate coverage. No official engineering study was done to verify this. I voiced a stong concern over spending this much money without properly engineering a system. I would caution you to do the same. If you invest all that money into a system and it does not give you good coverage it could look bad for you.
Just ask the Connecticut State Police. Motorola sold them a sweet 800mhz digiatal system for several million dollars and the coverage stinks. There are currently not enough tower sites for the officers to be in line of site which is critical for 800mhz operations. Officers in some locations have to use their personal cell phones to contact their dispatcher at times!!! Not to good if you ask me.
To date we have not aggressively pursued any major changes. Our county dispatch center recently went through a major upraged where we isntalled PC controlls for our radios and a CAD system. For now the system will remain in place until such time we can accomodate the major changes.
Hope this helps. Good luck on whatever you decide to do. Please keep us posted.
Mark
If you are going to use a voting repeater system in your area you must make sure that you have sufficient coverage otherwise you will be plauged by dead spots. Also when I talked to some other agencies that went to a voting repeater system they had the following issues. Of the agencies that used RF to link their sites initially, all of them swithced to either Microwave or hardline. The voters apparently had significant problems recieving the signals from the remote sites and could not properly isolate the strongest RX signal. This resulted in significant audio quality problems. The two problems with switching are; Microwave is expensive up front cost. Leasing hardlines form the phone company are expensive long term cost.
Our town which operates its own police department and dispatch center has looked into using cell tower as sites for a town only voting repeater system. Even with free space the up front hardware costs for this system are huge. Initial estimates are close to $750,000. Pricing was based on budgetary quotes on Daniels Electronic System and Tait radios. These are high end radios designed for this type of service. We are looking at 5 sites within our 38 sq. mi. town. This study also assumed that the towers we were looking at would give us adequate coverage. No official engineering study was done to verify this. I voiced a stong concern over spending this much money without properly engineering a system. I would caution you to do the same. If you invest all that money into a system and it does not give you good coverage it could look bad for you.
Just ask the Connecticut State Police. Motorola sold them a sweet 800mhz digiatal system for several million dollars and the coverage stinks. There are currently not enough tower sites for the officers to be in line of site which is critical for 800mhz operations. Officers in some locations have to use their personal cell phones to contact their dispatcher at times!!! Not to good if you ask me.
To date we have not aggressively pursued any major changes. Our county dispatch center recently went through a major upraged where we isntalled PC controlls for our radios and a CAD system. For now the system will remain in place until such time we can accomodate the major changes.
Hope this helps. Good luck on whatever you decide to do. Please keep us posted.
Mark
"Also licensing for the VHF RX and TX freqs, and for 4 UHF freqs."
You don't need to license the VHF freqs at the sites if you are not transmitting.
You are correct about using 4 different UHF freqs. Commonly, more than one site will RX the VHF signal and key up the links. Two links on the same freq keyed at the same time =bad. A critical part of voting systems depends on having extremely clean links. You don't want the link causing the noise that prevents the site being voted.
The system you described is common and has been done.
Here is a good link to check out:
http://www.jps.com/downloads/PDFS/snv12app.pdf
Good luck!
-SZ[/quote]
You don't need to license the VHF freqs at the sites if you are not transmitting.
You are correct about using 4 different UHF freqs. Commonly, more than one site will RX the VHF signal and key up the links. Two links on the same freq keyed at the same time =bad. A critical part of voting systems depends on having extremely clean links. You don't want the link causing the noise that prevents the site being voted. The system you described is common and has been done.
Here is a good link to check out:
http://www.jps.com/downloads/PDFS/snv12app.pdf
Good luck!
-SZ[/quote]
Yea, I meant to license that before. You don't need to license the recievers. I'm not sure off the top of my head what the code is for a link transmitter. Probably F Something Somenumber.
"I'll eat you like a plate of bacon and eggs in the morning. "
- Some loser on rr.com
eBay at it's finest:
Me: "What exactly is a 900Mhz UHF CB?"
Them: "A very nice CB at 900Mhz speed!"
- Some loser on rr.com
eBay at it's finest:
Me: "What exactly is a 900Mhz UHF CB?"
Them: "A very nice CB at 900Mhz speed!"
"You don't need to license the VHF freqs at the sites if you are not transmitting."
True enough, but who ever your frequency co-ordinator is (APCO etc.) should be advised of where the receivers are. An agency (who shall remain nameless) that I know of is dealing with "interference" now, one theory is that they "forgot" to include several remote receivers in the information they furnished to the co-ordinator. As a result they have a new co-channel user a bit too close to some of the "forgotten" sites.
<edit to protect the innocent>
True enough, but who ever your frequency co-ordinator is (APCO etc.) should be advised of where the receivers are. An agency (who shall remain nameless) that I know of is dealing with "interference" now, one theory is that they "forgot" to include several remote receivers in the information they furnished to the co-ordinator. As a result they have a new co-channel user a bit too close to some of the "forgotten" sites.
<edit to protect the innocent>
-
N4DES
- was KS4VT
- Posts: 1234
- Joined: Thu Dec 25, 2003 7:59 am
- What radios do you own?: APX,XTS2500,XTL2500,XTL1500
If an agency lisenses their "Protected Service Area" correctly for the talk-back frequency with the coordinator there is no reason to tell APCO where the receive sites are as APCO doesn't keep a database of satellite receive sites. All they care about is what is on the FCC application and there is no place to list the individual RX sites.
At my former agency we had an average of 20 RX sites for each of the 3 district VHF channels and 36 receviers on the 2 County-Wide channels and never once told APCO or anyone else. It would be a complete waste of time.
At my former agency we had an average of 20 RX sites for each of the 3 district VHF channels and 36 receviers on the 2 County-Wide channels and never once told APCO or anyone else. It would be a complete waste of time.
Simulcast
We have multiple simulcast systems in our area, U, V and 800. The MAIN advantage to simulcasting is this - penetration! With one transmitter site you will get good on street coverage, but your talk out will suffer inside buildings (malls, restraunts, office buildings).
The voting system will help talk in, but unless you pulling a Nextel (low site, very high poer, flat land) you will be disappointed in you talk out.
KC4COV aka N8OXA
The voting system will help talk in, but unless you pulling a Nextel (low site, very high poer, flat land) you will be disappointed in you talk out.
KC4COV aka N8OXA