Antenna misalignment is becoming a bigger problem Right now, an arms race is underway in the LTE sector, as commercial carriers race to stay ahead of the competition and to keep up with the data demands of their customers. That means a lot of new towers are being built, and many others are being converted from older technologies to 4G LTE. That, in turn, is causing headaches for both the carriers and their contractors, because the coverage and performance from the site often is less than expected. The biggest culprit is antenna misalignment, according to John Vetter, vice president of Sunsight Instruments, which manufactures the AntennAlign alignment tool. Vetter estimates that about half of all tower sites have some sort of antenna-alignment problem, with roughly 40% having an antenna’s azimuth off kilter by 10 degrees or more. The cumulative effect of such misalignment is enormous, he said, particularly in the LTE space, which utilizes more sites than 2G and 3G cellular, and many more than land-mobile radio (LMR) networks. When antennas are misaligned, interference is created, coverage is affected and spectrum is used inefficiently. Vetter said that the interference issue is particularly problematic for data transmissions. “Voice wasn’t that big of a deal—you could have overlap and a poor signal, but you could still get a call through,” Vetter said. “[But] with data, if you have coverage overlap and interference, you’ve just driven up your noise floor; therefore, you … get less throughput for the users on that sector.” The time to find out about such problems is when the tower crew is still onsite, given that it can cost a contractor several thousand dollars to send another crew to correct the problem. “They’ll modernize a site for LTE, and then do a drive test because they did an antenna swap-out, and they realize that the coverage is off,” Vetter said. “Why? Because nobody used any sort of alignment tool. These guys pay up to half a million dollars for a cell site and, at the very end, they don’t make sure that the cell site matches the RF design.” Exacerbating the problem is that there is a shortage of experienced tower workers right now, because of the aforementioned arms race, but Vetter said that even experienced crews struggle with antenna alignment. “There are a lot of green crews out there,” Vetter said. “But there are a lot of people out there who are starting to realize that this is a problem, even if they have a quality crew—there still could be issues with human error. … A lot of the bigger [contractors] are using us, because they don’t want to do rework, they want to do new work.” The AntennAlign tool works in a manner similar to that of a carpenter’s level. First, target values for the antenna are loaded into the tool; this can be done in advance or onsite. Then, the tool is attached to the antenna using a “very secure” mounting device to establish four contact points, in order to capture measurements for azimuth, tilt, roll and height, Vetter said. The tool compares those measurements to the target values. If something is off, the technician simply manipulates the antenna and measures again. This continues until the antenna is properly aligned according to the four parameters. Once that happens, the antenna is locked down and the tool generates a report that confirms all is well. The tool offers 20 hours of battery life, is IP 65-rated for water and dust resistance, and has survived falls from 200-foot-tall towers. “It’s very durable,” Vetter said. It’s not cheap, costing $10,000, but given that it can cost as much as $5,000 to deploy a three-person crew to correct an antenna’s alignment, avoiding just two such truck rolls will pay for the device, according to Vetter. Vetter added that antenna misalignment is not just a problem for the cellular carriers and contractors—it also can be vexing for public-safety answering points. “There’s all of this data for [Enhanced]-911 Phase 2 and Phase 1,” Vetter said. “What happens is, they think the antenna is pointed to zero degrees true north, when it’s actually pointed to 120 degrees, so the call gets routed to [the wrong PSAP] because the antenna was pointed in the wrong direction. That’s a response-time issue."
Posted on: Sun, 21 Jul 2013 15:41:02 +0000
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