Radio Interference Measuring Has Changed

     WASHINGTON (CN) - The Federal Communications Commission has issued regulations to protect AM radio station signals from distortion caused by communications towers and other structures.
     The process of "proofing," or "proving" a tower will not cause interference with other signals, will now be made easier by replacing the physical process of measuring an array of points in relation to a tower with "moment method" computer modeling, the action says.
     This relatively new method employs software that does the measuring, calculations and other processes for engineers, saving time and money associated with conducting much of the proofing process in the field.
     Proofing antenna systems is particularly important to AM radio tower operators.
     Unlike other towers, AM radio towers function as the antenna, which makes AM signal patterns vulnerable to interference caused by other towers, such as broadcast or wireless operators.
     "A nearby tower may become an unintended part of the AM antenna system, reradiating the AM signal and distorting the authorized AM radio pattern," the FCC said in its action.
     The new regulations are meant to help avoid that problem.
     If the modeling shows the new or modified tower would distort the AM pattern by more than 2 decibels, the operator is responsible for installing a detuning system. A detuning system adjusts hardware to cancel out AM radiation.
     All communication services are subject to the new regulations, which requires them to provide notice to any nearby AM station of their intent to build or modify a tower at least 30 days before construction. The notification provision also applies to buildings or any other structure where a new antenna may be built, or an existing one modified.
     The FCC says the new regulations are based on proposals by an ad hoc technical group of radio broadcasters, equipment manufacturers and broadcast consulting engineers that make up the AM Directional Antenna Performance Verification Coalition.
     The regulations are effective Dec. 5.