Radio (BDA) Systems: Public Safety Radio

Posted by ORR Protection on Jan 20, 2021 9:00:00 AM

During the MCFP Virtual Conference series, Dal Brazzell, Sales Manager at ORR Protection Systems, discusses Radio (BDA) Systems. Part 2 of 3.

Video Transcript:

So now all of the design and installation requirements were here. The only thing that was really left back in 72 was referenced to pathway survivability and interface into the fire alarm systems. And then again, in 2019 and the current version of code that's out now, there were some further changes that are really driven again through the contract and community, because of the difficulty in meeting pathway survivability level two, or level three in an existing building they've now changed the code. So that only the riser in backbone really needs to be level two or level three. And there's obviously a hard preference for that to be in a two hour rated, protected vertical chase of some sort. But they've backed off of the requirement for pathway survivability so that the pathway survivability only needs to match the building's fire rating.

So if the building only has a one hour fire rating, then the circuit only needs to be protected for one hour, that doesn't make sense to have a two hour protected circuit. So it limits the expenses of the installation and requirement for special cabling and wiring. So the different types of systems that are, that are on the market or the different types of wide area. So these are the countywide citywide systems. There are a lot of different bands available on the market and not everybody uses the same band. So historically you'd see a lot of folks using the UHF bands, the VHF bands UHF is going to be between 450 and 520 megahertz. VHF is going to be between 150 and 174 megahertz. Those worked great and rural environments because of it's long wavelength that travels a long distance. So you, you get a lot of coverage from one tower.

But the problem with UHF VHF historically has been those bands aren't set aside for public safety use. So you've got a lot of nonemergency traffic on the UHF and VHF bands, and that creates a problem because if you've got a lot of band traffic in an emergency situation, you can create problems with the reliability of the in-building system, if you're amplifying non-emergencies. So signals on top of the emergency signal. So you'll see over the last few years has been a big move towards 700 megahertz and 800 megahertz signal. So most cities have started to adopt the 800 megahertz band. And this is going to be the most common, it's a set aside band specifically for emergency use. It can be available as a digital frequency or an analog frequency. It can be trunking system so that you can have, you know, police, fire and EMS all on the same band and the same user sharing the same system.

The problem with an 800 megahertz is it doesn't because it's an, it's a short wave link, short wave links. Don't travel through building materials very well. So concrete steel, low E glass, really creative major problems and filtering out that outside radio signal from coming inside of the building. But again, the benefit of that system is it is set aside 100% for emergency responders. 700 megahertz is also set aside for emergency responders. There's some, a fair amount of adoption on the 700 megahertz band, but you won't see as much there on, on the 800 megahertz, or sometimes you'll see a combo dual band system, whether you 700 and 800 megahertz. And again, the same, same problems here is the 700 megawatts. It doesn't really penetrate a building well. So the key message here is you may have a city where the fire department is using an 800 megahertz system and the police department is still using UHF VHF, or you may have one using UHF and the other using VHF.

So not all emergency responders in any given jurisdiction use the same band. So the definition this system is not just a fire system, it's it's to help all emergency responders in a building. Again, in the case of a school shooting in the case of a fire or any type of issue where you might have the police that also needs to be able to communicate inside the building. So you really have to understand who's going to be using the system, what bands they're going to use, and then you have to select the correct technology to amplify each band. And you may have to have multiple amplifiers if you have multiple bands. So component subcommittee of the wide area public safety radio system, obviously you're going to have your handheld radios to your typical handheld radio has a small amplifier. It's normally gonna transmit that signal anywhere from a two and a half to a five watt signal out of the handheld radio mobile and vehicle radios are obviously going to have more power than a handheld radio, and they're going to go 25 to 50 Watts.

And then your actual tower repeater amplifiers are normally going to be anywhere from 50 to 300 plus Watts per amplifier. And this is important because the code says it's not just important that the people in the building receive the signal, but they also have to be able to transmit the signal. So code requires you have to have less than 95 DBM of loss on your uplink signal and less than 95 DB of signal loss on your downlink signal. So if you're only broadcasting two and a half to five Watts from your handheld radio back to the tower, and you're 10 miles away from the tower, obviously you're going to have more signal loss because you're starting with a smaller power system than you would on your downlink where you're broadcasting may be on a 200, 300 watt amplifier. So again, it is key to understand you've got to have both that uplink and downlink signal strength.

So the way the signal strength is measured again, is what they call a DBM that's decibels per milliwatt of broadcast, again, as the radio signal travels through the air, it travels through objects again, particularly concrete steel and Lowy glass. It's going to filter that signal out and you're going to have loss of strength. So normally if you're outside of a building for a good rule of thumb and you've got better than 82 DBM of loss, you're probably going to be okay without installing a radio system or radio enhancement system within the building. But normally if you've got a, a reading outside of a building, or if you're on a job site before the building's built, and you've got more than 82 DBM of loss, you're almost always going to need an emergency responder radio communication system, just because of modern building materials, all glass now, as low E glass and with lead construction the building materials are really going to filter out the, the radio signal.

So obviously the, the signal loss here is measured as a negative. So a negative 95 is better than a negative 100 on the system. So there's two ways to measure your signal strength. So in the early versions of the code, there was a reference to the performance requirements to have less than 95 DBM of loss on the uplink and downlink signal. But later versions of the IFC and the NFPA have switched over to what they're calling DAQ and DAQ is delivered audio quality. And that's very similar in the fire alarm world to intelligibility. So it's not just how strong is the signal, but it's how well you can understand the signal on the other end. So this is a measurable metric of the signal quality. And basically that's on a, that's on a scale of one to five and all all systems have to provide a system that where speech is easily understandable.

So DAQ of four is going to give you speech that's easily understandable with little noise and distortion four and a half is going to be rarely noise or distortion, and five is going to be perfect as you start to get below four speeches, understandable without permission, but you may have some distortion or noise in the background, and obviously you should drop below two. You really start to struggle to understand that signal. So it's, you don't want to have these levels. So there is there's some carry over and not all jurisdictions use the DAQ measurement and not all jurisdictions use the the DBM measurement. So again, it's important to know on the front end of the project if you're trying to meet the, the 95 DBM requirement or the requirement for the DAQ, so components of the in-building system you know, they're actually fairly simple.

They're, they're difficult to design, but they're, they're, they're fairly simple from a bill of material standpoint. So you normally have what's called the BDA some, some folks and some codes still reference this system as the signal booster, but your BDA is a bi-directional amplifier. So it amplifies the signal in the building and amplifies the signal out of the building. And normally that, that this is an example of what the bi-directional amplifier looks like. Normally that's going to be up on the upper floor of the building. If you've got a multi-store story-building, it's going to have an input and an output. And obviously on the input side, it's going to be connected to what they call a donor antenna and the donor antenna, or a Yagi antenna is normally on the roof or the wall of the building outside. And it's pointed towards the repeater tower for the jurisdiction.

And it's taking the signal off the air from outside as the input to the BDA, then the BDA amplifies that signal and pushes it out through the coaxial output through what they normally call the DAS or the distributed antenna system. And your distributed antenna system is going to be a number of antennas throughout the inside of the building. And each of these antennas are connected back to the BDA through a coaxial cable, and they're connected through splitters what's commonly called splitters or power dividers or couplers and just like any electrical system or a sprinkler system, or an air sampling smoke detection system. As you have additional length of coaxial cable, you lose signal loss for every foot of cable, you lose signal loss through your directional couplers and splitters, and you lose signal loss through your actual connectors on the co-ax and to the antenna.

So it's a calculated and highly engineered system to make sure that you've got the right output strength at the antenna inside the building. So it's, it's, it's critical that the, the, the couplers be installed in the correct location and the co-ax is installed properly in the wire's not kinked. So on and so on. So there, there are several different types of BDA systems on the market, and some jurisdictions have a preference for one over the other. So there's, without going into a lot of detail, there's what they call a class, a BDA and a class B BDA and some, some cities will specify only a class, a and some specify only a class B. So again, it's important to know when you're writing a specification or if you're a contractor and you're doing a checkout on a, on a project for your subcontractor, that if the engineer's asking for a class a, that what you actually got as a class, a, and not a class B or vice versa.

So all of these systems have to be installed by a licensed FCC individual with what they call a R O L or a general radio operator's license. And the system itself actually has to be registered with the FCC when it's installed one again, one key point. Obviously this is going to be an example of, of one of the types of interior antennas. You've got an example of a power divider here, or a directional coupler in addition to, to the bi-directional amplifier, which has to be mounted within a two hour rated space, you also have to have a remote annunciator or remote monitoring panel for the bi-directional amplifier, that's actually installed in the fire command center, or within a certain number of feet of the actual fire alarm control panel. So that when the fire department responds to the fire alarm control panel, they can see the, the status of the, of the BDA.

Topics: Featured Article, Featured Blog, MCFP

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