Large Coverage Area, Thinking of installing two repeaters

[madfrenchie]

Good Afternoon everyone.

Our local fire department is having issues with our single repeater providing coverage throughout our fire coverage area.

Ill try to draw you a mental picture of what we currently have. We have two fire stations, One in Town(Station 1), and one at the Lake(Station 2 about 20 miles away from station 1)

Station one has a repeater up on a mountain in town. If you are sitting at Station 2, you are able to receive the signal from the repeater, but the 5 watt portables are unable to transmit to the repeater.

We want the ability to place a second repeater at Station 2, that will allow the portables to reach the primary repeater.

What we basically want is full coverage throughout our fire coverage area.

What i would like to have, is basically two receivers and two transmitters. If someone is in the station 2 area and transmits, I would like it to repeat at the station 2 repeater as well as the station 1 repeater, both on the same frequency. I believe there is a way to sync the two repeaters so they can both broadcast on the same frequency.

We have two VHF frequencies, one for repeater input and one for repeater output. we also have a bunch of extra 400Mhz frequencies that we use to use for old RF up links, we don't want to the repeaters linked by any hard lines, we would prefer RF Up links between the two, for redundancy, we have had alot of issues with phone / power lines going down.

Ive looked at voting repeater setups before, but they usually only had one transmit site, and two or more receive sites, I'd like this setup to have two relieve sites, and two transmit sites, and it has to be seamless, as trucks from station one always respond to fires at station two.

Any help would be appreciated. I'm basically looking for other people's opinions and ideas. I have a few myself, but would just like more input.

Thank You.

[Tom in D.C.]

Since the repeater can be heard at both locations why not install a remote receiver at the lake and link it back to the repeater? You wouldn't have to sync anything if you did that. You would still need an additional receiver and a transmitter, of course. We use UHF links in my area that cover up to 100 miles quite reliably.

[madfrenchie]

Since the repeater can be heard at both locations why not install a remote receiver at the lake and link it back to the repeater? You wouldn't have to sync anything if you did that. You would still need an additional receiver and a transmitter, of course. We use UHF links in my area that cover up to 100 miles quite reliably.

My initial idea is basically what you said, using our 400 Mhz frequencies that we still own for the uplink.

Station 2 Station 1

Reciever ----------> Transmitter --------------> Reciever -----------> Repeater Transmitter
158.880 400Mhz 400Mhz 154.100


And also


Station 1
Reciever ----------------> Repeater Transmitter
158.880 154.100




But the chief said if we are going to be making changes to the system, he wants to go all out and set it up with two repeater systems link together to transmit the same received signal. Now i know this isn't simple, as the two transmitters need to be in phase or something, so that the received signal doesn't sound like its being walked all over (pardon the wrong terms used, i know the concept, i just don't know the proper terms)

So id like to find the best solution for this second scenario. and what this type of system would technically be called.

Thanx again for your response tom.

[tvsjr]

If the chief wants to spend the money, you need to forget doing "ghetto" linking to try and make it work.

There are two technologies that you need to consider:
Voting - this involves having multiple receivers and selecting the best to be repeated
Simulcast - having two or more transmitters keyed up on the same frequency simultaneously.

Voting is somewhat complicated. Simulcast is more complicated. If you can hear the repeater throughout the district on an HT, then I would avoid simulcast... just add a second receiver at the lake.

You'll need a voter (JPS SNV-12, for instance) and some way to get the audio from the secondary receive site to the repeater. This could be an RF link, wireline, or a wireless shot (4.9GHz recommended, if you can make the path).

Making voting work involves ensuring the audio path is carefully aligned, but it's not massively difficult.

Simulcast requires that both transmitters are calibrated to each other with a very small margin of error. This is typically done with a reference at each site and careful alignment. Allowable frequency error is minute. Get it too far off and you have heterodyne.

My suggestion would be that you talk to some local radio shops who have experience with these types of systems. Making a repeater work is one thing... making a voting simulcast system work is quite another - orders of magnitude more complex. Not to be critical, but from reading your post, you either need some help making it all happen, or you need to be prepared for a very steep learning curve ahead.

[madfrenchie]

If the chief wants to spend the money, you need to forget doing "ghetto" linking to try and make it work.

There are two technologies that you need to consider:
Voting - this involves having multiple receivers and selecting the best to be repeated
Simulcast - having two or more transmitters keyed up on the same frequency simultaneously.

Voting is somewhat complicated. Simulcast is more complicated. If you can hear the repeater throughout the district on an HT, then I would avoid simulcast... just add a second receiver at the lake.

You'll need a voter (JPS SNV-12, for instance) and some way to get the audio from the secondary receive site to the repeater. This could be an RF link, wireline, or a wireless shot (4.9GHz recommended, if you can make the path).

Making voting work involves ensuring the audio path is carefully aligned, but it's not massively difficult.

Simulcast requires that both transmitters are calibrated to each other with a very small margin of error. This is typically done with a reference at each site and careful alignment. Allowable frequency error is minute. Get it too far off and you have heterodyne.

My suggestion would be that you talk to some local radio shops who have experience with these types of systems. Making a repeater work is one thing... making a voting simulcast system work is quite another - orders of magnitude more complex. Not to be critical, but from reading your post, you either need some help making it all happen, or you need to be prepared for a very steep learning curve ahead.

Thank You!!

This was extremely informative. I agree with you that the best way to do it wold be one single repeater with two receivers. It would be the simplest way to go about getting the whole thing working. The problem around here, is there are no local radio shops at all. So everything has to be basically taken care of in house.

Thanx again for all the info provided.

[ai4ui]

Even if you simulcast you are going to want to vote the inputs to the repeaters because it would just plain sound weird to anyone in the overlap area if you were clear into one repeater and noisey into the other and both were transmitting what they received.

[Bill_G]

Good morning Frenchie. This is my bread and butter. As has already been discussed, to do this right, you need both a voting system, and a simulcast controller to do what you want because the primary repeater covers the entire area. Without strong technical support, it would be impossible to get it done correctly. Both are simple conceptually, but require a degree of precision that comes at a price.

Can we assume that budget is also an issue?

While we are at it, has your department started work on narrowbanding yet?

Without a radio shop, who would perform the work?

The simplest, least technical, and lowest cost approach would be to install a second repeater on different channels at station 2 - assuming station 2 can be received at station 1, and all your radios have scan. It's a terrible option, but it would work with a strong wind at your back on days with a full moon and a clear sky. Maybe.

The next level of complexity would be to improve the inbound coverage of the primary repeater with a rcvr preamp. This is something well within the grasp of most radio shops, but still requires some consideration, and could easily reduce coverage if done wrong.

Tells us about your system. What model of repeater is it? What model of duplexer? What model of antenna? What kind of coaxial cable is used? How high is the antenna on the tower, and is it well above the tree canopy? Are there any site noise issues, or adjacent channel issues?

If you send me the lat and long of the rptr hilltop, and sta 2, I can plot a coverage map that would tell us what is needed to make a single site system work.

ps - Your understanding of the problems is excellent, and your use of terms is close enough. We'll do our best to give you a hand. At least point you in the right direction.

[madfrenchie]

Good morning Frenchie. This is my bread and butter. As has already been discussed, to do this right, you need both a voting system, and a simulcast controller to do what you want because the primary repeater covers the entire area. Without strong technical support, it would be impossible to get it done correctly. Both are simple conceptually, but require a degree of precision that comes at a price.

Can we assume that budget is also an issue?

While we are at it, has your department started work on narrowbanding yet?

Without a radio shop, who would perform the work?

The simplest, least technical, and lowest cost approach would be to install a second repeater on different channels at station 2 - assuming station 2 can be received at station 1, and all your radios have scan. It's a terrible option, but it would work with a strong wind at your back on days with a full moon and a clear sky. Maybe.

The next level of complexity would be to improve the inbound coverage of the primary repeater with a rcvr preamp. This is something well within the grasp of most radio shops, but still requires some consideration, and could easily reduce coverage if done wrong.

Tells us about your system. What model of repeater is it? What model of duplexer? What model of antenna? What kind of coaxial cable is used? How high is the antenna on the tower, and is it well above the tree canopy? Are there any site noise issues, or adjacent channel issues?

If you send me the lat and long of the rptr hilltop, and sta 2, I can plot a coverage map that would tell us what is needed to make a single site system work.

ps - Your understanding of the problems is excellent, and your use of terms is close enough. We'll do our best to give you a hand. At least point you in the right direction.

Wow.. that was a mouthful, ha, Let me try to answer you to the best of my ability.

To start off with, "The Money" We are working on a grant right now that will take the money problem out of the picture, well sort of... Of course we need to keep costs as low as possible.

There is a radio shop available to us, that for an EXTREME cost will make the trip up to survey our area, and discuss with us all the possibilities, and then once we figure out what we want (after spending thousands of dollars just "Talking" with them) they will install it. So what I am trying to do is gather as much information as possible, and use my knowledge (I've been dealing with the local system here for years) to provide the radio shop with a plan and say "Here this is what we want" That would save us a lot of money!

So again, I thank you all for your help.

Now, As far as two separate repeaters with different frequencies, this answer falls in the same boat as "are we narrow band ready" The answer is Yes and No. We have all our applications filled out, we have been slowing upgrading all our radios / pagers and are well on our way to being "Narrow band Compliant" The problem is the FCC hasn't issued new frequencies in northern Maine for YEARS, and won't be issuing any new ones till after this whole Narrow banding issue is out of the way. (were looking about 2 to 3 years before any new frequencies are available to us)

As far as it goes with coverage, Yes, station 1 can reach station 2, but station two is much lower then station 1, therefore a tower at station 2 most probably would not reach station 1. I had the same basic understanding that you mentioned, a Voting system, coupled with a simulcast system, and honestly I think this is the way I am leaning to for the best possible clarity of signal, and coverage area. (there are some places at the lake where station 1 doesn't reach very well, if at all) we are dealing with a very large coverage area, our furthest reach is about 1/2 hour drive from Station 1, which is about 15 minutes from Station 2, not to mention that we have to Haul all our water with us in the station 2 coverage area. So clear communications is a MUST.

Now... what do we have for a system. Well this is something I will have to answer in a later post, I will gather up the model numbers of our *duct tape and wires system* (its an old system, don't laugh) and will post all that info as soon as i gather it all, *I have a horrible memory, so model numbers isn't something i keep at the tip of my tongue)

The location of our tower is
Location: 47-19-47.1 N, 068-20-54.2 W
Site Elevation: 3323.1 meters
Tower Height: 100.6 meters
Tip of Antenna reaches 101.8 meters

Repeater is 100 Watts.

Again, more info will be provided later once i grab the model numbers and info you asked for above.


thanx!

[ai4ui]

The problem is the FCC hasn't issued new frequencies in northern Maine for YEARS, and won't be issuing any new ones till after this whole Narrow banding issue is out of the way. (were looking about 2 to 3 years before any new frequencies are available to us)

Looking at that statement, I have to wonder if you will have issues getting a license for a second transmitter. Even though its on the same frequency, in the already licensed contour, the FCC may view it as if it were a new frequency. Either way, you are going to have to contact a coordinator.

We tried to move a repeater to a lower site 8 miles south of the original site with just a modification and was denied - had to go to the coordinator even though the new contour was smaller than and inside of the original contour.

As far as the money, well, everyone is going to be standing around with their hand out...

[Bill_G]

Frenchie - I think you guys need to have the repeater serviced. The plot doesn't look too horrible at all if my assumptions are right.



100w into a duplexer with +2db loss, up 110m of 1/2 inch Heliax with another 3db loss, puts about 30w at the stick. Assuming 3db gain for the antenna yields an outbound plot that covers the area pretty well. The inbound plot shown above is a different matter. Assuming 5w handhelds into the same antenna with the same losses to a receiver with .5uv/-113db sensitivity shows inbound range is greatly reduced, but still usable. There is very little green (excellent signal) along Long Lake, a majority yellow (some hiss to noisy), and a few red areas (failure) towards the SE end.

This system should work if everything was in good condition. You would have greater outbound than inbound on portables, but that is normal. Your mobiles would have the same range as the repeater.

I suggest the following maintenance work be performed:
*Have the repeater serviced paying attention to the receiver. We want -113db or better sensitivity.
*Have a receiver site desense test done, and if greater than 1db, determine the source. It could come from the duplexer, the coaxial cable, loose connectors, a failed antenna, corroded guys on the tower, corroded joints in the tower, a chain link fence, another tower close by, a broadcaster, another transmitter in the area, etc. It could be difficult to hunt down.
*Have the duplexer tuned and/or replaced with a good pass/reject set of cavities.
*Have the antenna and feedline swept with an analyzer like an Anritsu Site Master looking for corroded connectors, and other failures.

I suggest the following upgrades to the receiver system:
*Improve the coaxial cable to 7/8ths inch Heliax to cut your line losses in half.
*Replace the antenna with a 9db offset dipole with the elements aimed SE (about 145 degrees). Unless you mutual aid with Canada, you might as well put most of your energy where you will use it.
*Add a crystal filter to the receiver line if site desense or adjacent channel noise are issues that can't be resolved otherwise.
*Add a preamplifier to the rcvr to bring the sensitivity down to -120db. Certainly add a preamp to overcome the losses a crystal filter introduces.

If you make all these improvements, the inbound coverage will look like this.



Hope that helps.

For those interested in a better explanation of the plots: green is 20db higher than the receiver threshold, yellow is 0 to 19db higher, and red is below threshold. The threshold is defined in the plot parameters. The first plot assumed -115db threshold with 6db line and cavity losses and 3db omni gain antenna; the second plot assumed -120db threshold, 4db line and cavity losses, and 9db directional gain.

[madfrenchie]

Very interesting, I'm going to review what you said deeper tomorrow morning, but if you look at your maps, you see where Long Lake is. Our station 2 is at long Lake, and we cover all around the lake plus an extra 10 to 15 mile distance past that

[Bill_G]

I can adjust the center of the map further south after you give us more information about the system. That repeater location should be great for your area. I had to add impairments and reduce confidence quite a bit until the plot showed fair to poor coverage in the Long Lake area as you described. That is how I came to the conclusion some basic maintenance is needed.

[madfrenchie]

I can adjust the center of the map further south after you give us more information about the system. That repeater location should be great for your area. I had to add impairments and reduce confidence quite a bit until the plot showed fair to poor coverage in the Long Lake area as you described. That is how I came to the conclusion some basic maintenance is needed.

Yeah, i talked with the Chief, and we will have access to the tower next week so I can provide you more info, I really like those maps you created, when looking at it, its pretty darn close to what we actually do get for coverage on RX from HT's

[Bill_G]

That's good to hear. Thanks. Sometimes I am too conservative with my assumptions making the coverage too small. This adds weight that something is impairing your system. Once that has been determined, and corrected, you should enjoy much better coverage over the whole county without investing in an overly complicated solution. Even if ultimately you invest in a new repeater with new new line and new antenna, you probably do not need a simulcast. On the other hand, a voter would help fill from the south. There are always holes in a system, and voters are well understood.

Where do you guys dispatch out of?

[madfrenchie]

That's good to hear. Thanks. Sometimes I am too conservative with my assumptions making the coverage too small. This adds weight that something is impairing your system. Once that has been determined, and corrected, you should enjoy much better coverage over the whole county without investing in an overly complicated solution. Even if ultimately you invest in a new repeater with new new line and new antenna, you probably do not need a simulcast. On the other hand, a voter would help fill from the south. There are always holes in a system, and voters are well understood.

Where do you guys dispatch out of?

Ha, no laughing at this one, The local paper company hires a 3rd party security firm to manage their security, it is this security firm that dispatches us.

We have one Repeater for Fire, one for Police, one for Ambulance, one for Public works and one for High School. all at the same location.

The dispatcher just uses a basic mobile radio as a bast station, and dispatches us using QCII tones.

Most of the guys have Minitor III's some of us seasoned guys have Minitor IV's with stored voice, and the newbies are given Minitor II's

The officers have Motorola HT 1250's, I just recently acquired an XTS2500I Model III for my use. works great! Some of the trucks have MCS2000 Model II and my personal car has a MCS2000 Model III. We also have other various Motorola radios, and a few Kenwood HT's

[Bill_G]

I've seen that before. We have a local private ambulance company that also dispatches towing and taxis. You do what you gotta do.

[madfrenchie]

I've seen that before. We have a local private ambulance company that also dispatches towing and taxis. You do what you gotta do.

Just as long as they don't dispatch a tow truck to an ambulance call. hahah...

[Bill_G]

They could do worse. They began decades ago as an ambulance service before ems was common - family run mortuary with vehicles large enough to carry patients and crew. Now, they have a full call and dispatch center for their own EMS advanced care cars, patient transfer, and mobility services. They contract out as an answering and dispatch service for towing, taxi, airporters, and private limos without leaving their mortician roots behind. Ingenious and enterprising family.

[madfrenchie]

One stop shop for all your needs. haha...

for YEARS we were calling our dispatch center by the name of the paper mill, well the mill recently got bought out, so we have a new name for our dispatch center, it gets confusing on the radio sometimes, people mistakenly calling it the old name, getting no response, and then having to call again!!