During a recent meeting with an electrical contractor, we were asked “What are some best practices for DAS installation”?
We thought we’d share a Q & A session with Ryan Smith, a Systems Design Professional with Day Wireless, discussing some of the best practices to keep in mind when installing a Distributed Antenna Systems (DAS). Ryan started his career at Day installing DAS systems and now he designs them, so he has a good perspective on both the hands-on and technical aspects of the job.
What happens once you get the go-ahead on a DAS project?
Once we get a contractor approval we’ll come up with the final design and we’ll put together a submittal package. We’ll design a package that we know should pass Authority Having Jurisdiction (AHJ) inspections, because having done multiple projects with various cities, we know what they are looking for. The package will show the cable pathways, equipment lists, the data sheets and there’ll be some detail, because if someone’s never put a system in they’re not going to know what exactly needs to be done in a jurisdiction to pass inspection.
Now when I was working out in the field doing DAS installation, when we were delivering the cable and parts to the contractors, I would hold a class. I would go out and demonstrate some of the essentials, such as how to put a connector on the coupler, how you tell where your coupler needs to go, how you connect it up, how you install the antenna, for maybe an hour. For the most part, if I did that we wouldn’t have any problems.
Electrical contractors are very capable of doing DAS installations, but investing just an hour of training up front can save many hours on the back end cleaning up mistakes.
What would you say are some best practices to remember when installing cable for a DAS system?
First off, don’t use any kind of electronic cable puller, unless it’s absolutely necessary. There are multiple instances where it gets kinked because of the electronic puller. You should be manually pulling that coaxial cable.
In pulling a cable, a rope is put through the conduit and tied to the cable and pulled back through the conduit. But an electric puller is moving in a circular motion, which twists the cable, and you can see where it gets kinked, especially on plenum cabling. Plenum cable has an air dielectric which means the inside of the cable is mostly air. You have your outer conductor and your center conductor. Between them on standard cable you’ll have foam but on plenum cable it’s just air. Because the plenum cable is mostly air, it’s not as sturdy, and a lot easier to crush, kink, and damage. The plenum cable has to be pulled by hand. Any kind of device similar to an electronic cable puller will ruin it really easily.
When you’re pulling by hand it’s a really long process, right?
Yeah. But that’s not the area where you want to take shortcuts.
Do you need to run DAS coax in a different cable tray then standard cable?
It depends. Usually on something like an apartment there’s not going to be a cable tray so we’re securing it to the side of a wall every three feet. Obviously you don’t want to run it with the electrical wiring and, depending on the code, you’re not supposed to run it with other signaling cable like cat 6. Some places its fine, some places it’s not.
Our (Day Wireless) coaxial cable is very well shielded so I don’t think it’s going to be a problem running with cat five or cable TV if you can do it above the suspended ceiling. We definitely want to keep it away from electrical wiring. The other thing is keeping in mind of the bend radius, it’s like five-inch bend radius on most hardline half-inch coax. That’s important obviously coming around turns and bends. It’s really easy to kink this cable if you’re not careful. Especially the plenum.
Even if you have a lot of space to make a turn, at what point would you use a jumper?
I have seen some sharp turns where they would cut the cable and connect the jumper to make it around, but each time you’re doing that you’re weakening the signal. It’s not the preferred method. The preferred method is doing I guess what you’d call a kind of wide bend around the 90 degree turns.
What other tips do you have for making installs a little easier?
We try to order spools small enough to move around easily and fit through doorways. That seems like a no-brainer but it’s something we’ve learned over time. I know we would try and limit to 500’ coaxial spools. Cabling is heavy; 500 feet of coax weighs over 100 pounds. Safety is a consideration with such large sizes and weights.
You also don’t want to be hauling around large spools while trying to get it in place on a job site, you want it to be manageable. Think about a 2000’ spool of coax that might be on a 4-foot-tall roll. I can’t even fit that in my pickup.
What is line sweeping, why is it important, and what are some of the best practices for line sweeping for DAS installations?
Line sweeping can get quite complex with RF technicality but, simplifying it a bit, we are trying to make sure the various coax runs fall within the calculated “engineered” specifications. You’ll have a guide if you’re sweeping to an antenna for load or your return loss, and a lot of times it’s kind of basic. You set your limiter to around 15 db and if it gets above that you have a problem.
I’ve gone to turn systems on where the lines weren’t swept, and there’s a problem somewhere and who knows where it could be. Sometimes it’s challenging to figure out where the problem is. Sweep lines as you go to make sure you’re in good shape.
What’s the best way to document that?
We have reports where we’ll label a run as cable 23, for example. You go in on the map and see that cable 23 going from point a to b, and then you put a reading next to it. It’s not hard, it just takes time because you have to move your ladder from spot to spot, but obviously it’s a lot easier to come in when cables are exposed, especially if it’s new construction and it doesn’t have a ceiling lid in. Customers are not too happy when you have to put your hands in the ceiling. I get some dirty looks when we’re having to cut holes in a finished ceiling. I can recount many times where sweeping would’ve saved a lot of hassle.
What are some of the final requirements of the DAS system in order to pass the fire inspection?
We need dedicated power for the equipment permit generally, a 20-amp circuit. Also all of our equipment is required to be NEMA 4, which provides extra protection against moisture and wind. Most of the bi-directional fire signal boosters and battery backup manufacturers will meet that.
Another thing we need for public safety is to connect to the fire alarm panel at multiple points. Generally, we’ll provide a demarcation of the point where the signal booster is, where the batteries are, and we’ll run all the alarm wires to one little point terminal strip and this is usually the last thing done. Literally we’re doing it hours before the final fire inspection. Obviously we need to get it straight for the final sign-off.
One thing electrical contractors are interested in is the fire code and how to wrap the coaxial cables for 2 hour rating.
We’re going back to the fire code, which I talk about all the time. Make sure you understand your local code in and out. In most cases it’s the donor and the riser, the vertical cabling is required to be protected. If you’re running vertical you know your cable and conduit will need to be two hour fire-protected. As of right now, 2-hour fire-rated coax does not exist. One of the ways to meet code is with fire wrap. If you wrap it, it’s very, very expensive and very time consuming.
What would you say are the common mistakes you see made by DAS installers?
- Connectors are one of the most common mistakes, not knowing how to connectorize the specific kind of coax properly.
- Pulling coax with an electronic device and kinking the cable.
- Incorrect coupler installation. With a coupler, there’s an in and out and a tap. If you mix that all up, you can definitely unbalance the system. These things can all be easily avoided with some basic training and planning.
If you have questions about a DAS system installation, contact our expert team who are skilled at distributed antenna system design, site inspections, coverage testing, and system installation.