Cap+ Antenna Setup

[yaknamedjak]

Howdy RF wizards,

I'm planning to donate a UHF Capacity Plus system to my alma mater, a non-profit boarding school. My plan is two XPR8400s (with a spare).

They have a great antenna location with a 5-story castle-like building right in the middle of the campus. The middle section of the building is 2-stories higher than the rest, think dungeon tower.

The roof of that tower is 50x30ft. There's some other equipment up there like lightning detector and weather cams.

Most of the subscribers will be on the ground or in buildings within 1/4mi. of the tower.

With two XPR8400's, let's say at max power for fun, what would be the ideal (cost-effective) antenna setup regarding antennas/combiners/filters? If you could ELI5 I'd appreciate it, links would be great. We will be having an electrician do any actual antenna install and cable runs to make sure it's grounded appropriately, etc, but I'd like to keep the equipment cost down as much as reasonably possible.

One repeater pair is 46x.2625 (5mhz separation)
Second repeater pair is 46x.3125 (5mhz sep, on the same mhz). We have a another repeater pair at 46x.4375 if that helps.

I know the answer is to go to the radio shop nearby but I wanted to hear from this braintrust before someone tries to sell me something..

 

[mmckenna]

Howdy RF wizards,

I'm planning to donate a UHF Capacity Plus system to my alma mater, a non-profit boarding school. My plan is two XPR8400s (with a spare).

Before you donate, make sure you work out the licensing/frequency coordination. Many schools will just see it as a gift and figure "someone else" took care of the licensing. Make sure they understand that the license IS required and WILL need to be renewed every 10 years.

They have a great antenna location with a 5-story castle-like building right in the middle of the campus. The middle section of the building is 2-stories higher than the rest, think dungeon tower.

The roof of that tower is 50x30ft. There's some other equipment up there like lightning detector and weather cams.

Most of the subscribers will be on the ground or in buildings within 1/4mi. of the tower.

With two XPR8400's, let's say at max power for fun, what would be the ideal (cost-effective) antenna setup regarding antennas/combiners/filters? If you could ELI5 I'd appreciate it, links would be great. We will be having an electrician do any actual antenna install and cable runs to make sure it's grounded appropriately, etc, but I'd like to keep the equipment cost down as much as reasonably possible.

It would be difficult to know which antenna will work well without knowing the local topology. 1/4 mile makes it pretty easy and you should not need high power/high gain antennas to make this work. In fact, you should have the transmitter power output and ERP established as part of the frequency coordination process. It's not a free for all, install whatever you want. There are rules/requirements about sharing frequencies.

A low/medium gain antenna would be sufficient. Folded dipole types work well and are super durable (if you get good name brand ones, not Chinese junk).

Choosing antennas would depend on the radiation pattern needed, kind of hard to tell you much without knowing more. This is one of those places where a good radio shop can look at the site and give you some good ideas. A good consultant would use propagation modeling software to make sure as many variables as possible were considered.

One repeater pair is 46x.2625 (5mhz separation)
Second repeater pair is 46x.3125 (5mhz sep, on the same mhz). We have a another repeater pair at 46x.4375 if that helps.

That's awful close spacing on those two. Is that what the frequency coordinator gave you, or did you get those from somewhere else? You'll need a rather expensive TX combiner to make that work.

I know the answer is to go to the radio shop nearby but I wanted to hear from this braintrust before someone tries to sell me something..

Yeah, well there is a good reason for that. Goes along with not relying on a hobby website to design a radio system. Not bashing you, just making it clear that there is some serious knowledge that is required, and you'll save a lot of money doing it right the first time.

I'd also recommend that you do NOT use an electrician to do any of this work (other than maybe establishing the suitable ground points). Electricians do not have the knowledge to properly set up a radio system, choose the right parts, properly install coaxial cable, tune TX combiners, and test out the system.

I know, not what you want to hear, but there is a very good reason you'll get people telling you to bring in a good radio shop. And I do mean an actual radio shop. Not the local ham radio club, or someone's step brother that has installed a CB in his van.
The test equipment required to set this up is way beyond an electrician or a hobbyist.

You won't be doing the school any favors by having someone install a system improperly and ignoring the FCC rules.

 

[AK9R]

You won't be doing the school any favors by having someone install a system improperly and ignoring the FCC rules.

Or, installing a system that presents a lightning hazard to the building. Or, installing a system that the school comes to rely on only for it to fail in a critical situation.

 

[yaknamedjak]

Thanks for your reply, mmckenna. I've learned a lot from your posts over the years.

Before you donate, make sure you work out the licensing/frequency coordination. Many schools will just see it as a gift and figure "someone else" took care of the licensing. Make sure they understand that the license IS required and WILL need to be renewed every 10 years.

Yes. No plan to do whatever we want, all within guidelines. Just providing the current information. Currently they have an analog license with 8 frequencies (four repeater pairs) that were frequency coordinated just under 10 years ago, I help them acquire the license. They were issued repeater pairs in case they one day wanted to add a repeater. These were licensed only for analog portables, so as part of this I was going to help them work with the frequency coordinator to modify the license for this use-case. Perhaps that will require changing the frequencies, yes.

I'd also recommend that you do NOT use an electrician to do any of this work (other than maybe establishing the suitable ground points). Electricians do not have the knowledge to properly set up a radio system, choose the right parts, properly install coaxial cable, tune TX combiners, and test out the system.

Not planning to choose any parts from an electrician, but understood.

It would be difficult to know which antenna will work well without knowing the local topology. 1/4 mile makes it pretty easy and you should not need high power/high gain antennas to make this work. In fact, you should have the transmitter power output and ERP established as part of the frequency coordination process. It's not a free for all, install whatever you want. There are rules/requirements about sharing frequencies.

A low/medium gain antenna would be sufficient. Folded dipole types work well and are super durable (if you get good name brand ones, not Chinese junk).

Choosing antennas would depend on the radiation pattern needed, kind of hard to tell you much without knowing more. This is one of those places where a good radio shop can look at the site and give you some good ideas. A good consultant would use propagation modeling software to make sure as many variables as possible were considered.

Just wanted to get some recommendations on brands/models of equipment required in between the antenna(s) and the radios and how best to install them...assuming omnidirectional 1/4mi coverage. It's low-lying trees in the rural south-east. Not a lot to deal with. This building/antenna site is the tallest within 15 miles other than a water tower a few miles away.

there is a very good reason you'll get people telling you to bring in a good radio shop.

While in Public Safety I heard terrible things from the county about the local Moto shop, so if another one could do design and part-spec remotely, that would be ideal. Happy to work with a radio shop, just wanted to put out some feelers as there are a lot of great minds (some scrooge-y) on here, and I like having multiple sources of information before making decisions.

and ignoring the FCC rules.

I know a lot of people ask a lot of questions on these forums, and you reply to many. I'm sorry that this was your assumption as this isn't me.

 

[mmckenna]

Thanks for your reply, mmckenna. I've learned a lot from your posts over the years.



Yes. No plan to do whatever we want, all within guidelines. Just providing the current information. Currently they have an analog license with 8 frequencies (four repeater pairs) that were frequency coordinated just under 10 years ago, I help them acquire the license. They were issued repeater pairs in case they one day wanted to add a repeater. These were licensed only for analog portables, so as part of this I was going to help them work with the frequency coordinator to modify the license for this use-case. Perhaps that will require changing the frequencies, yes.

Yeah, if the original coordination included actual pairs, then you are part way there. Having not used them for 10 years may present some challenges if someone else is using them locally (a possibility)
Also, if you coordinated them for analog, you do want to go back and get the frequency coordinator to recheck things as DMR plays a bit of a different game than analog. They'll want to know so the license can be updated, at minimum.

Having two transmitters means that a simple duplexer isn't enough, you'll need a proper transmit combiner, and it needs to support 500KHz spacing between channels.

Not planning to choose any parts from an electrician, but understood.

OK, good. I do use electricians for some work, like establishing grounding bars properly tied into building/electrical ground, running conduit, and brining in AC power, but that's where I stop and either do the rest myself, or bring in a radio shop.

Just wanted to get some recommendations on brands/models of equipment required in between the antenna(s) and the radios and how best to install them...assuming omnidirectional 1/4mi coverage. It's low-lying trees in the rural south-east. Not a lot to deal with. This building/antenna site is the tallest within 15 miles other than a water tower a few miles away.

Since the antenna is the most important part of the system, you'd want to invest well here. Not uncommon to spend as much on the antenna system as the repeaters themselves. For 1/4 mile coverage, I'd probably be looking at a set of folded dipoles or a 3-5dB gain vertical, but I'm in the hilly/mountainous part of the US, so my experience may not match up well with the flatter parts.
I've been using a number of Telewave folded dipoles on a UHF system I'm responsible for. The area gets some pretty nasty weather and their stuff has stood up well for many years. There are other companies, but that should get you started.

Frequency coordination does absolutely play into things here. If the original coordination/license does not include repeaters, then you need to add that. The frequency coordinator will look at the existing license and look at other co-channel users and help you make sure you don't get/cause interference. That'll come out as how much power and how much antenna gain you can run. Talk to them and get that taken care of before spending money on any equipment.

While in Public Safety I heard terrible things from the county about the local Moto shop, so if another one could do design and part-spec remotely, that would be ideal. Happy to work with a radio shop, just wanted to put out some feelers as there are a lot of great minds (some scrooge-y) on here, and I like having multiple sources of information before making decisions.

Really depends on your approach and how hard you stand your ground. Most radio shops would show up and try to tell you that you can't use those repeaters, need to get all new equipment, buy way more than you need, and magically find a way to spend the entire budget + 10%.

If you stick to your guns and make sure they know they are just using existing gear and you absolutely do not have a budget for new stuff, they will be easier to deal with.
But, understand, they may not be willing to work with the old equipment, and probably will not guarantee anything unless you are buying new from them. That could get sticky right there.

And there are plenty of other radio shops than Motorola.

I know a lot of people ask a lot of questions on these forums, and you reply to many. I'm sorry that this was your assumption as this isn't me.

Understood. There are a lot of people with really good intentions out there. Often they think this is super easy to do, and will often start buying equipment off e-Bay or Amazon first, then want someone to help them hook it all up. When FCC is mentioned, they realize they missed a step and want to ignore it.

Glad you understood where I was coming from there.

Sounds like you have a good plan. I'm sure the school will appreciate it the time and effort you are putting into it. A good solid radio system will likely make their lives easier and they'll really benefit from it.

 

[yaknamedjak]

Thanks so much for all this great info.

Having two transmitters means that a simple duplexer isn't enough, you'll need a proper transmit combiner, and it needs to support 500KHz spacing between channels.

Appreciate it - this is the spec I was looking for - understanding that the frequencies may change and requirements could get more lenient...hope they do.

OK, good. I do use electricians for some work, like establishing grounding bars properly tied into building/electrical ground, running conduit, and brining in AC power, but that's where I stop and either do the rest myself, or bring in a radio shop.

This is exactly how I utilize the sparkies on the network infrastructure side! I'll let them hang devices too...like access points and cameras....if I've built trust with them, ha.

a set of folded dipoles or a 3-5dB gain vertical

Thanks I'll start looking but won't pull the trigger until the license/freqs are sorted. This is in rural VA, definitely different than CA.

Frequency coordination does absolutely play into things here. If the original coordination/license does not include repeaters, then you need to add that. The frequency coordinator will look at the existing license and look at other co-channel users and help you make sure you don't get/cause interference. That'll come out as how much power and how much antenna gain you can run. Talk to them and get that taken care of before spending money on any equipment.

Copy that - will be sure to address that first and will follow up on this post. Very rural area so I'm optimistic. Currently they are using MagOnes on the freqs analog.

Most radio shops would show up and try to tell you that you can't use those repeaters, need to get all new equipment, buy way more than you need, and magically find a way to spend the entire budget + 10%.

That's what I'm used to...but you're right I'll give it a shot.

Understood. There are a lot of people with really good intentions out there. Often they think this is super easy to do, and will often start buying equipment off e-Bay or Amazon first, then want someone to help them hook it all up. When FCC is mentioned, they realize they missed a step and want to ignore it.

Glad you understood where I was coming from there.

Sounds like you have a good plan. I'm sure the school will appreciate it the time and effort you are putting into it. A good solid radio system will likely make their lives easier and they'll really benefit from it.

100% on all fronts.

I've got some 7550s, 3500e's, and 4550's already that I was hoping to use a starter, which is why I was thinking Cap+ would be a great fit if the license can get modified. As you said, that will be the starting point...


Totally understand. I should have mentioned FCC-awareness in my first post. We all appreciate the time you put into providing valuable information on this forum as well, so thanks again.



Will try to keep this thread updated as the project progresses and if anyone has additional input feel free to chime in.

 

[yaknamedjak]

Update: I spoke with the frequency coordinator yesterday and we are going to add two new repeater pairs to the license. The existing frequencies were in a group that allowed low power (~6w) only. The existing frequencies we will keep on the license (for TACs) with both analog and digital so that some of the TACs can communicate with the existing 4w analog portables.

The new proposed pairs have just under 3Mhz between their outputs which helps with @mmeckenna's point about combiner tolerance, so that's cool.

I mentioned a 3db vertical and he thought that would be good with the surrounding area and coverage area. That brings us to about 100W ERP which he concluded was acceptable.

It was a progressive first step. Next I'll be reaching out to a company he suggested to spec the combiner/duplexing equipment and hear their recommendations.

 

[kayn1n32008]

If you are giving them 2 repeaters, then they should be combined to use a single antenna. You won't need to run them anywhere near full power if they only need a 1/4 radius of operation. If they already have a bunch of repeater pairs coordinated, use 2 of them, and modify the license for 7k0 DMR emissions.

 

[alcahuete]

The experts have spoken and provided you with some outstanding advice, as always.

I have to ask a couple questions though to get you thinking:

1. Are you just using a repeater because you have the equipment laying around, or is there an actual need? I would almost think that simplex would work fine over the 1/4 mile, both inside and outside of the building, but maybe not. Just asking.

2. Are there ever going to be more than 2 simultaneous talk paths in use, to where CAP+ is even necessary in the first place? Things would be greatly simplified with a single repeater (not needing a combiner, worrying about interference, etc.,), and you would still get two simultaneous talk paths via the two timeslots.

 

[yaknamedjak]

Thanks for these questions. Definitely appreciate the input!

1. Are you just using a repeater because you have the equipment laying around, or is there an actual need? I would almost think that simplex would work fine over the 1/4 mile, both inside and outside of the building, but maybe not. Just asking.

While most of the subscribers will usually be within 1/4 mi radius of the proposed tower, the simplex is not currently handling the half mile through buildings that this diameter covers. It's close but there are a lot of "fuzzy" areas based on reports. The furthest distance from the tower that I'd like ensure coverage is 1.21 miles.

2. Are there ever going to be more than 2 simultaneous talk paths in use, to where CAP+ is even necessary in the first place? Things would be greatly simplified with a single repeater (not needing a combiner, worrying about interference, etc.,), and you would still get two simultaneous talk paths via the two timeslots.

It's tough for me to say. Initially when thinking about donating radio comms to them, my answer would have been that I think you're right and two would be enough for 90% of the comms. Now that we have done some light fleet mapping, we are up to 37 subscribers over 24 talk groups, I'd rather have the third talk path available. It's not so much the number of subscribers in this case but the number of discreet groups that need to communicate with each other such as athletics, maintenance, landscaping, housekeeping, etc. They also hold a lot of events on campus such football games, cross country meets, etc that will probably burst over 2 talk paths.

 

[alcahuete]

Thanks for these questions. Definitely appreciate the input!

While most of the subscribers will usually be within 1/4 mi radius of the proposed tower, the simplex is not currently handling the half mile through buildings that this diameter covers. It's close but there are a lot of "fuzzy" areas based on reports. The furthest distance from the tower that I'd like ensure coverage is 1.21 miles. The campus is that big.


It's tough for me to say. Initially when thinking about donating radio comms to them, my answer would have been that I think you're right and two would be enough for 90% of the comms. Now that we have done some light fleet mapping, we are up to 37 subscribers over 24 talk groups, I'd rather have the third talk path available. It's not so much the number of subscribers in this case but the number of discreet groups that need to communicate with each other such as athletics, maintenance, landscaping, housekeeping, etc. They also hold a lot of events on campus such football games, cross country meets, etc that will probably burst over 2 talk paths.

All makes sense.

 

[yaknamedjak]

I just wanted to post an update to this thread and reiterate my appreciation to everyone who replied and provided input. On Monday, April 29th a vendor came and did a great job installing the antennas I provided, two unity gain Laird FG4500s. They installed polyphasers and connectorized everything, as well as provided jumpers for my rack equipment. This included a two channel Sinclair TX Combiner and a 1 in, 4 out Sinclair RX Multicoupler. Two kenwood 5w in, 100w out amplifiers take 5w from the repeaters and give it some juice.

Yes, it’s older gear, but it’s got life left in it. I’ve got a spare repeater on hand, and with Capacity Plus, if one craps out the system stays online, reduced to one usable talkpath.

Coverage is great for their needs so far. I’ll go back in a couple months to get some better metrics, but portables get out to at least two miles with heavy trees in the way. Closer to 80 portables are live now, with some additional as well as some mobile radios going in on the next visit.

 

[buddrousa]

Thanks for the update looks like you built them a very nice system they are lucky to have someone like you. Yes people can build a good system and save a little money at the same time just as long as no shortcuts are taken good job.

 

[kayn1n32008]

'...ensure coverage is 1.21 miles.... Now that we have done some light fleet mapping, we are up to 37 subscribers over 24 talk groups, I'd rather have the third talk path available. It's not so much the number of subscribers in this case but the number of discreet groups that need to communicate with each other such as athletics, maintenance, landscaping, housekeeping, etc.

100wERP for 1.21 mile of coverage is over kill. 10wERP is probably more than enough. I was with a club that had a repeater that was less than 25w ERP and provided mobile coverage with a radios of about 80km.

As for the 'light fleet mapping' uh... yea... 0.65 talkgroups per subscriber on the system. The fire department, for a city of over 1 million people, has 22 talkgroups. This isn't including any shared interop talk groups. This is just thier own agency talkgroups.

That's some serious over kill. At that point you might as well just solely use private call. I would seriously figure out how to cut that down to a maximum of 16 talk groups and only have one zone.

If nothing else, set up a logging computer for 6 months and see how many of those talk groups have any PTT activity.