AM Protection - Dealing with Legacy Towers – Technical Note 119

A significant number of wireless towers have changed hands, frequently without supporting documentation that AM protection measures have been taken to comply with the Federal Communications Commission Rules.  In addition to tower owners, licensees engaged in collocation activities are often discovering that documentation cannot be found for existing towers where they propose to locate equipment. Since all licensees, but not tower owners, are required to comply with FCC AM protection rules, guidance for procedures regarding tower detuning and other AM protection action on “legacy” towers assumes considerable importance in the collocation equation. This paper suggests cautions and a recommended sequence of events for licensees collocating on these legacy towers.

Requirements for AM protection:

Across the nation, LBA has seen recently increased concern about how the intent of the FCC rules should be satisfied by licensees, tower owners and AM stations (47 CFR §22.371 is germane and has been interpreted to apply broadly to all licensees).  Critical to the FCC’s intent is the liability of the wireless licensee, not the tower owner, to ensure that AM protection actions are taken.  However, LBA has seen that the tower owner also maintains a civil liability that is subject to judicial rights of redress, as well as a fundamental responsibility to its collocated carriers.  There may even exist local zoning conditions requiring AM protection, to say nothing of public relations risks.

Indeed, licensees expect that the tower on which they are to co-locate is maintained in accordance with all appropriate regulations prior to its installation.  The only entity that can effectively assure compliance is the tower owner.  Most leases represent this responsibility as well.  To not effect this assurance, one is jeopardizing the licensing responsibilities of every carrier on the tower, since each licensee may be considered to hold “joint and several” liability for the tower reradiation of a nearby AM station’s signal.

In one case, inadequate AM protection was provided, and the radio station attempted to assess each carrier significant damages, as well as to compel the tower owner to undertake expensive remediation actions.  Had timely action been taken, these measures would have been largely unnecessary.  We note also that the FCC has recently levied forfeitures for failure of carriers to notify construction to the radio station.

Actions required for Legacy AM protection:

It is LBA’s opinion that actions should be based on the intent of the AM protection rules set by the FCC.  These require AM notification before any licensee activities can begin on your site that could affect the AM radiation pattern.  AM coordination and documentation to demonstrate no impact are essential.  That means that each individual collocation or modification requires notice!  Furthermore, a very important aspect of the rules requires maintenance of detuning, if installed, throughout the life of the tower.  There is a dynamic, life cycle responsibility to AM protection.

For a constructed tower that is occupied by one or more licensees and has no indication of prior notification, coordination or documentation actions, diligent efforts to put the tower into compliance are necessary and should be initiated immediately upon realization of this liability.  If liabilities are found to exist, this will entail AM protection tower audits, identification of existing documentation, determination of follow-on actions by collocated carriers and notification and coordination with the AM.

Licensees should be aware that rectifying a delinquent AM protection situation by merely installing a detuning skirt  and declaring the tower compliant can backfire!  Not infrequently, over time, an AM station will have altered station operations to accommodate the existing environment, including the licensee’s tower.  When the tower is detuned, that station may have to readjust its pattern.  As a consequence, the licensee may be called upon to fund these pattern adjustments as well.  However, if the station has relicensed to include your tower effects, there may be no cost liability to the licensee.  These things require careful and expert study to resolve, but offer a big payback.

Measurement and documentation plans for a “legacy” tower also must be established on an individual project basis.  The fundamental purpose of the measurements is to prove that your AM protection actions have produced the desired result.  Without adequate pre-construction or pre-modification measurements as a base line, this becomes increasingly difficult to accomplish, since many AM stations are chronically out of compliance with their licenses for reasons having nothing to do with the legacy tower--and for which the licensee does not want to pay to fix!

We recommend that licensees ascertain that new towers have undergone all required AM protection measures and are “clean”.  Then, as tenants are added, standard policy should be to ensure that each conducts appropriate AM protection measures as a condition of its lease.  

In summary, LBA recommends licensees and site managers:

• Have LBA initiate immediately an audit of all your tower sites to see if AM protection is required.  
• For those within the geographical protection boundaries, review your files for documentation showing that AM station notification and follow-up action have been taken with respect to the tower and each licensee’s tenancy.  
• If no such information exists, or is incomplete, establish with LBA a plan for mitigation and/or documentation of no impact.  
• Inform tenants of any delinquent actions and coordinate a resolution strategy.
• When the resolution strategy is adopted, notify the AM station involved and have LBA coordinate implementation of the AM protection activities with the AM station.  
• Fully document the program and report results as required.
• Maintain a dynamic program of AM protection management for the towers, to avoid future problems and to ensure lifecycle functioning of detuning systems.





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LBA Group companies serve technical infrastructure needs related to the broadcast, wireless, electromagnetic compatibility and safety sectors worldwide. We provide consulting, training and other telecommunications industry services. We also produce and market hardware for radio transmission, RF shielding, safety and testing.