There may be no greater need for cellphone signal boosters than inside the thick concrete walls of a large multi-dwelling unit (MDU) building. That is the application facing Waveform in Southern California as it designs and installs boosters for a nine-story condo complex in Kirkland, Wash.
The structure has 30 to 35 units per floor, plus two underground levels. In all the building is 350,000 square feet. The cellphone booster design and installation are complicated by the fact that the building is a retrofit project. The condo complex was gutted and designed to target young professionals, most of whom rebuff the need for landlines and use strictly cellular phones.
The six-figure project came from a referral from a previous client into design engineer Shawn Colwell, who says the original scope was just the two underground floors and the first two above-ground floors.
“A couple of months went by and they wanted a quote for the whole building,” recalls Colwell.
So where do you start in designing a system like this?
“I started at the rooftop where we did a site survey,” says Colwell. “We got the rooftop readings for literally every carrier, every band. We found the weak ones and ran just an antenna network, calculating gain and loss in the cable. Then the amplifiers are able to work very well with each other on the same system, so we have multiple SureCall Force5 units located throughout the building.”
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From a signal design standpoint, the building is separated in half — west side and east side — with each having its own utility closet. There are eight antennas per floor. Each Force5 will cover approximately 15,000 square feet, conservatively.
“The units can do more than square footage than that but for the sake of cabling, and ease of installation, this [design] was less expensive. Each amp will have four antennas but there are eight per floor,” notes Colwell.
The antennas themselves are located at the most feasible locations, which in this case were the hallways. Using the spherical pattern that emanates from the antennas for the layout, Colwell made sure the units were not placed too far apart. The antennas are connected using LMR-400 and LMR-600 coaxial cable, which is two to three times thicker than RG-6.
“With about 85 percent probability, we can estimate the coverage for each carrier. It’s not always going to be equal, but we can pretty much estimate how much coverage those antennas are going to provide,” says Tom Hernandez, director of operations and sales.
The interior concrete walls were the biggest challenge. The building design meant there were a lot of firewall locations. It required a two-man crew going back and forth with measurements to pinpoint solutions for the problem areas. Colwell responded by putting in more antennas and spacing them out more cleanly.
Meanwhile, other new buildings are being constructed nearby that could affect the cell signal in the future because they will overwhelm the capacity of the cell towers, but the cell repeaters will mitigate that problem if it occurs.
“If the signal environment does change on the outside, it’s rare. We will send an installer back out to do a little re-balance. In this situation, it would obviously be a lot of labor, but if AT&T loses 10dB on the roof, you have to adjust all 21 amplifiers. It’s pretty mathematical at that point,” adds Colwell.
At the Kirkland project, which is only about 65 percent complete, The Repeater Store is running nearly two weeks over budget in terms of man hours due to the concrete walls and tight regulations in Washington. Also, since it is a union state, it meant the California-based company had to purchase insurance and register as a business, among other things.
“We’ve learned in our experience that it’s not so much connecting the parts, but the real art and success and value we bring to the table is our ability to maximize the signal coverage using the equipment,” says Hernandez.
That means calibrating the uplink and downlink signal levels on the amplifiers for each carrier band and each type of carrier signal
