RADIO AND TELEVISION BROADCAST ANTENNA

Radio and television broadcast stations transmit their signals via radiofrequency radiation (RF). This radiation is regulated under N.J.A.C. 7:28-42. Signals from broadcast antennas can be a significant source of RF radiation in the environment. The amount of this radiation to which a worker or member of the general public can be safely exposed is determined by the frequency of the radiation. Broadcast antennas transmit at various RF frequencies, depending on the channel, ranging from about 550 kilohertz for AM radio up to 800 Megahertz for some UHF television stations. Frequencies for FM radio and VHF television lie between these two extremes.

Broadcast stations are usually located near densely populated areas so that the signals can be received by large audiences. The radiation patterns from broadcast antennas are not as highly collimated as are those from other sources of RF radiation, such as microwave aperture (dish) antennas and satellite earth station antennas. Therefore, exposure of persons to main-beam, radiation intensities near the broadcast antenna is possible, especially if individuals are at eye level with the antenna bays, as may be the case for residents of high-rise buildings. The intensity and location of the radiation fields from broadcast antennas depends on several factors, including the type of station, the characteristics of the antenna being used, the power transmitted to the antenna and distance from the antenna. Usually, calculations can be performed to predict what field intensities would exist at various distances from an antenna.

Public access to broadcast antennas is normally restricted, either through fencing, placement on a communications tower or installation in rugged terrain. However, there are some instances where overexposures of the general public may occur. In some cases, simple measures can be taken to prevent these overexposures, such as the installation of fencing or the posting of warning signs.

In cities, broadcast antennas may be located on the roofs of buildings and thus building maintenance personnel may unknowingly be exposed to RF radiation. Maintenance workers are occasionally required to climb antennas for the purpose of painting, making repairs or replacing beacons. In these cases, it is possible for a worker to be exposed to hazardous levels of RF radiation if work is performed on an energized tower or in areas immediately adjacent to an actively transmitting antenna.

Other sources of exposure to workers may come from the actual RF transmitter or in the case of AM radio, the tuning coil at the base of the transmitting antenna. Precautions should be taken to ensure that maintenance workers are not exposed to hazardous field intensities. Such precautions may include temporarily lowering power levels while work is being performed, broadcasting from an auxiliary antenna while work is being performed on the main antenna, having work performed only when the station is not broadcasting and/or establishing work procedures that would specify the minimum distance that a worker should maintain from an energized antenna.

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