AM Towers and Wireless Carriers can Profitably Partner By Lawrence Behr, Founder and CEO • LBA Group, Inc.
For years, wireless carriers looking for places to hang their antennas and coaxial cables looked everywhere except at AM radio broadcast towers. While the carriers undoubtedly were tempted to incorporate the existing towers into their expansion plans and save tens of thousands of dollars in erection costs, they usually concluded the AM structures were too much trouble. They were intimidated by the seemingly incompatible requirements of AM and wireless technologies. They were further discouraged by stringent Federal Communications Commission regulations that protect AM towers and broadcast patterns.
Their caution was totally understandable…then. Technological innovation has opened the way for cellular, PCS and SMR carriers to collocate on many of the estimated 10,000 AM structures in the United States.
Many AM station owners are increasingly willing to rent space on their structures, perhaps many more owners than generally is known. Because the heights of their towers fall below federal regulatory minimums, some station towers are not required to register their structures with the Federal Aviation Administration, which keeps an eye on towers as flight hazards. Not being listed, the towers for all practical purposes don’t exist to wireless system designers, which of course precludes the designers from making overtures to collocate. Hint: If tower owners want their vertical real estate in the collocation market, they are strongly encouraged to voluntarily register them with the FCC and FAA.
What sort of problems are used to discourage collocating on an AM tower? Most wireless carriers feared they would encounter difficulty in attaching their multiple antenna cables, but engineers have figured out how to carry the cables across the “hot” tower base without interfering with AM broadcasts. Station owners, meanwhile, needed assurance that the collocation method proposed by a wireless operator was reliable, acceptable to the FCC and no threat to the station’s signal coverage pattern. Such outcomes were not always guaranteed. Now that the station owners have been assured that attached antennas will not disrupt their AM signal patterns, they are quite willing to add a new stream of rental revenue to their bottom lines.
Other hurdles to collocation are mostly in the details of merging two technologies. AM and wireless cultures are different enough that experts in one area of engineering often are barely conversant with their peers in the other. AM broadcasting has evolved into a specialized field of lower frequency technology that can seem quite foreign to wireless system designers and constructors. Consequently, meshing the engineering and market needs of the two technologies, and coordinating the whole process with the FCC to ensure eventual license compliance, can be a headache. For this reason, and for other reasons I’ll mention later, station owners and carriers who bring in an experienced systems integrator early in the process save time and money.
The central engineering difficulty in collocations is the functional merging of the AM bandwidth “antenna” – the tower itself, which is the radiating element – with the self-contained wireless antenna and coaxial cable systems. This self-containment feature is what allows a wireless antenna to be affixed wherever suitable elevation can be achieved, even high on AM towers.
The solution to overcoming the dueling antenna properties is to isolate them. Two LBA Group, Inc. companies with more than 35 years of experience in AM broadcast and wireless industries collaborated to solve the problem. The companies developed a proprietary technological approach called CoLoSite. The essential hardware for the fix was developed and patented by LBA Technology, Inc. Lawrence Behr Associates, Inc. implemented necessary engineering and integration systems. Once installed, the system functionally isolates the radiating elements so completely that wireless antenna and coaxial cable installations have virtually no effect on the host AM tower and the AM signal has no effect on the wireless antenna.
Consequently, the number of wireless users on an AM tower is limited only by the tower’s structural capacity. Furthermore, if a tower owner subsequently decides to lease additional space to other wireless carriers, additional isolation devices are readily added without re-engineering the system because expansion accommodations are permanently incorporated into the AM system.
Non-directional and directional AM towers have somewhat different isolation needs, so LBA Technology developed different systems to accommodate the two types of towers.
The FCC stipulates radiation patterns for each directional AM station to ensure that one station doesn’t interfere with another station’s broadcasts. To form a pattern, directional stations employ multiple towers and the resulting pattern cannot be disrupted. While there is more than one way to collocate wireless antenna on a tower without disrupting the pattern, LBA’s cost-effective approach inserts an isolation system between the base station equipment and a tower.
The system, called CoLoCoil, prevents wireless transmission lines from interfering with the directional AM tower’s radiating signals. Because CoLoCoils are modular units, adding additional wireless antennas to a tower later is a simple mechanical process that hardly disturbs a station’s operation or a wireless carrier’s transmission.
On non-directional towers, an LBA system called CoLoPole typically is used. CoLoPole directly grounds an AM tower; wireless antennas and transmission lines are bonded directly to the structure. A unique wire cage impedance transformer is employed to match resistances and maximize the power transfer. The insulated cage is situated away from the tower for operational access. Besides empowering collocation, the system actually makes the AM station more efficient and further protects a tower against lightning. In other words, the fix gives station owners additional incentive to allow collocation on their towers.
In short, the actual conversion of an AM broadcast tower to multiple-use not only is technically feasible, it is a proven win-win situation for station owners and wireless carriers. On the other hand, successful transformations can’t be churned out like cut cookies. This is because numerous variables make each successful conversion a singular experience. Having a systems integrator on hand at the start of the process helps both parties negotiate complexities peculiar to a situation.
Consider the varying factors to be weighed in considering the addition of wireless antenna to an AM structure:
Is the station facility suitable for collocation? While each station theoretically is a candidate for conversion, some stations are not technically or economically practical to convert.
Which of a station’s multiple towers (where more than one tower exists) would be the most effective host for wireless antenna? The choice is not always clear and choosing wrong is an expensive mistake.
Will an AM station’s transmission schedule accommodate a carrier’s installation and maintenance needs? AM stations sometimes use different towers for day or night transmission, with power amped up or cut back at different periods. This schedule could affect a carrier’s efforts to install antennas and maintain them.
Is a tower readily accessible to construction / installation crews?
Is a tower’s load-bearing capacity sufficient for the addition of new antennas and other hardware?
How will hardware installation and tower reinforcement work be carried out to prevent damage to the AM station’s radial ground network of copper wire? Compliance with the FCC comes sharply into play here.
Are an AM tower’s high RF voltages fully understood in planning a conversion project? While AM stations need not always be shut down to install or maintain wireless antenna equipment, safety precautions approved by the FCC and OSHA are strictly followed. Collocation experts with AM know-how and RF credentials can spare companies lots of grief.
Where should the wireless equipment building be located and how much shielding and filtering is required? Electromagnetic field modeling lets experienced designers pinpoint the best locations for equipment packages.
What is a satisfactory lease or acquisition agreement? Negotiations can be as complex as the engineering behind it.
AM station owners and wireless carriers have plenty of reasons to come together now that technology allows it. In a tower, a station owner owns an asset he can leverage by inviting carriers to hang their hardware from it. As for a carrier, finding a suitable AM tower to share spares him expenditure of tens of thousands of dollars for construction of a separate tower; and that’s only if he can win approval of a tower from increasingly resistant zoning boards.
Tower collocation is working across the country for such wireless carriers as Sprint, ClearWire and AT&T. In all likelihood, the frequency of these tower mergers will increase once the word spreads that technological barriers to collocation have fallen.
Lawrence Behr is the founder of Lawrence Behr Associates, Inc., and subsequently, the LBA Group. Mr. Behr’s 35 years of experience span the areas of broadcast, military and commercial telecommunications technology. He has frequently served as an expert witness before the Federal Communications Commission, the courts and zoning authorities in communications regulatory matters. He presently is a director of the National Association of Radio and Telecommunications Engineers. He is a frequent lecturer and author and holds patents on several inventions in antenna technology. Lawrence can be reached at lbwireless@lbagroup.com.
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AM Towers and Wireless Carriers can Profitably Partner
What sort of problems are used to discourage collocating on an AM tower? Most wireless carriers feared they would encounter difficulty in attaching their multiple antenna cables, but engineers have figured out how to carry the cables across the “hot” tower base without interfering with AM broadcasts. Station owners, meanwhile, needed assurance that the collocation method proposed by a wireless operator was reliable, acceptable to the FCC and no threat to the station’s signal coverage pattern. Such outcomes were not always guaranteed. Now that the station owners have been assured that attached antennas will not disrupt their AM signal patterns, they are quite willing to add a new stream of rental revenue to their bottom lines.
The solution to overcoming the dueling antenna properties is to isolate them. Two LBA Group, Inc. companies with more than 35 years of experience in AM broadcast and wireless industries collaborated to solve the problem. The companies developed a proprietary technological approach called CoLoSite. The essential hardware for the fix was developed and patented by LBA Technology, Inc. Lawrence Behr Associates, Inc. implemented necessary engineering and integration systems. Once installed, the system functionally isolates the radiating elements so completely that wireless antenna and coaxial cable installations have virtually no effect on the host AM tower and the AM signal has no effect on the wireless antenna.