LBA Group’s successful June 16 webinar, under sponsorship of WCAI, was titled “AM Radio: Traps and Promises in Broadband Deployment.” The question-and-answer session that followed suggested a better title might have been… “AM Radio and Broadband Wireless can Co-exist? Really? I Didn’t Know That!”

Under-awareness of AM and wireless compatibility continues to run through the telecommunications industry like a rogue signal. This became clear in the questioning that followed the presentation by LBA chief executive Lawrence Behr.

After Mr. Behr technically explained why AM radio station towers across the country are a potential asset, not an obstacle, for wireless carriers, the questions rolled in. They ranged from how to locate an AM tower in a particular area to whether collocation is possible on the tower of a 50,000-watt station. And then there was the participant who asked, “Can I attach a wireless antenna to an AM tower and not use any kind of isolation equipment?”

AM Collocation Installation
AM Collocation Installation

Yes, Mr. Behr responded, but he would not be able to transmit any more AM signals. Clearly, even though the Engineering 101 principles of collocation are not unknown, they continue to elude many AM and wireless advocates.

“AM and wireless share the same physics, but practical aspects are vastly different,” Mr. Behr pointed out in the course of the webinar. Basically, AM towers are RF “hot” and radiate a signal in all directions, while wireless antennas typically are installed on “cold” towers, the sole purpose of which is to raise the antennas above the ground. Furthermore, AM signals are much more sensitive to structural interference than are wireless broadcasts.

To wed the two technologies on the same tower requires isolation engineering, which LBA Technology mastered some years ago. Its proprietary systems— CoLoSiteSM, CoLoPole® and CoLoCoil® —integrate AM and wireless functions while separating their RF natures. This harmony not only lets each system function, it is a revenue source for sometimes-strapped AM station owners. At the same time, it can be a cheaper, faster alternative for wireless carriers who otherwise must find a potential tower location, brave a zoning fight, and build a tower.

Yes, but what about the 50,000-watt AM stations—are they feasible collocation candidates? another participant asked.

“Well, 50,000 is indeed an elevated watts level to do a collocation system,” Mr. Behr observed. “But for the purposes of our discussion, such a station might have four different towers at the same site—a 30,000-watt tower, a 10,000, a 5,000, and another 5,000. You simply would select one of the lower powered towers for your antenna.”

He went on to explain that while a 50,000-watt station is feasible, even though it would require more engineering, it might not be a practical solution. A better solution could be to map the actual field strength around the tower to see what part of the site is lowest in RF intensity and then build a second tower at that site with a detuning system to eliminate the interaction. In that scenario, the station’s tower area would be a collocation site, rather than its tower becoming a collocation tower.

So some towers are better candidates for collocation than others? Yes, Mr. Behr told the inquiring webinar participant. “I had mentioned that some AM stations have multiple towers and those stations may be excellent candidates. A tower can be chosen that has minimum power and an operating schedule that is compatible with maintenance operations.”

On the other hand, he continued, “You may find various towers you won’t want to fool with, maybe because they are in less desirable locations, in swamps and such. Each site has to be evaluated, but I expect fully half of the AM towers across the United States are collocation candidates.”

A follow-up question: How can an engineer or wireless carrier find out if a tower spotted in a desired location will meet a coverage requirement?

“Clearly when the site guys are out in the field and scouting around, they may find these towers,” Mr. Behr said. “One problem is that many of the towers are not identified. Not only are they back away from accessible areas, many are under 200 feet and there won’t be any antenna registration numbers to track back.

“So the easiest thing to do is put in the principal coordinates in our tool at LBA, (The Tool Access Shown Here), and let it tell you who the tower belongs to, and its owner’s contact information, and so forth. If the station has another tower somewhere in the vicinity, that information will show up, too. Use the tool—it’s free—and see just what’s out there.”

The webinar presentation touched on two other solutions to AM and wireless conflict. One is for AM and wireless towers just to keep their distance from one another and avoid interference in the first place. The other is to “detune” a nearby tower that’s obstructing another’s signals so that the tower disappears in terms of its capacity to interfere.

The webinar—the slide presentation of which can be seen on the WCAI site here—also touched on the economics of collocations, meeting the safety needs of tower technicians, the impact of lightning on towers carrying AM and wireless signals, and the perspective of the Federal Communications Commission on collocation.

The bottom line: AM and wireless can co-exist. You probably heard it here first.

To discuss AM colocation options, contact Mike Britner at LBA Business Development or call him at 252-757-0279.

About The Author

LBA Group, Inc. has 50 years of experience in providing RF asset solutions and risk management for industrial and telecommunications infrastructure assets. The group is comprised of LBA Technology, a leading manufacturer and integrator of radio frequency systems, lightning protection, and EMC equipment for broadcast, industrial and government users worldwide; the professional engineering consultancy Lawrence Behr Associates, and LBA University, providing on-site and online professional training. The companies are based in Greenville, N.C., USA.

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