DX RX The Doctor of DX prescribes the answers to your problems, low and high, near and far. A how to of what for, by Mike(aka Billy)Graham, NE1V

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Evaluating RF Exposure
Part 1

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In August of 1997, the FCC's Office of Engineering & Technology issued OET Bulletin 65, Edition 97-01 titled "Evaluating Compliance with FCC Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields". In November of 1997 Supplement B was issued, titled "Additional Information for Amateur Radio Stations". These documents, in essence, define the methodology for determining if transmitting facilities, operations or devices comply with limits for human exposure to Radiofrequency (RF) fields adopted by the FCC. In addition, these guidelines apply to applications for FCC Station Licenses filed on or after January 1, 1998. The Commission has also specified a date of 1 September, 2000, by which time all existing facilities and devices must be in compliance with the new guidelines. Both OET Bulletin 65 and Supplement B thereto may be downloaded from:

In order to assist the members of the Nashua Area Radio Club in determining if an evaluation of facilities is required, this and the subsequent two DX Rx columns will discuss this subject. This month we'll discuss background and general information. In Part 2, we'll discuss specific requirements and evaluation criteria. In Part 3, we'll perform an actual evaluation, using a fictitious amateur radio station. It is also strongly recommended that each of you download the contents of OET Bulletin 65 and Supplement B, and retain copies in your files for future reference.

The FCC also revised its policy regarding transmitters, facilities and operations for which routine evaluation for compliance is required before granting an application. A routine evaluation is a determination as to whether the station conforms to the RF exposure requirements. For amateur stations, this requires that the station be subject to routine evaluation when it will be operated above certain power levels. In the past, although amateurs were expected to comply with the FCC's guidelines, routine evaluation was not required.

In August, 1997, the FCC issued revised technical bulletin OET Bulletin 65, that provides assistance and guidance to applicants and licensees in determining whether proposed or existing transmitting facilities, operations, or devices comply with FCC-adopted limits for human exposure to RF fields. Although Bulletin 65 provides basic information concerning evaluation for compliance, Supplement B was written to provide specific guidance to evaluation of Amateur Radio Stations. Although OET-65 and Supplement B offer guidelines for evaluating compliance, they do not establish mandatory procedures, and other methods and procedures may be acceptable if based on sound engineering practice.

The new FCC limits for exposure incorporate two tiers of exposure limits based on whether exposure occurs in an occupational or "controlled" situation, or in the general population or an "uncontrolled" exposure situation. General population or uncontrolled exposure applies to human exposure to RF fields when the general public is exposed and cannot exercise control over their exposure. Your neighbor's home is such an area. Occupational or controlled exposure applies where exposure is of a transient nature as a result of incidental passage through a location as long as the exposed person has been made fully aware of the potential for exposure and can exercise control over his or her exposure by leaving the area or by some other appropriate means. Your personal property can be considered as a controlled exposure area if appropriate restrictions on access to high RF field areas are maintained and educational instruction in RF safety is provided to individuals who are members of an amateur's household. Persons who are not members of the amateur's household but who are present temporarily on an amateur's property may also be considered to fall under the occupational/controlled designation provided that appropriate information is provided them about RF exposure if transmitters are in operation and such persons are exposed in excess of the general population/uncontrolled limits.

Section 97.13 of the Commission's Rules requires the licensee to take certain actions before causing or allowing an amateur station to transmit from any place where the operation of the station would cause human exposure to levels of RF fields that are in excess of the FCC Guidelines. The licensee must perform the routine evaluation if the transmitter power of the station exceeds the levels specified in the table below.

All Power levels are PEP input to the antenna. For repeaters, evaluation is required only if building-mounted antennas radiate >500W ERP, or if non-building mounted antennas are < 10 meters to lowest point of antenna and power >500W ERP.

No station is exempt from compliance with the FCC's rules and with the MPE limits. However, many amateur stations are categorically exempt from the requirement to perform a routine station evaluation for compliance. Mobile stations are categorically exempt from the above limits; but, it is advisable that mobile stations be considered for potential exposure before automatically applying the categorical exemption. As an example, a 500-watt, 10- meter mobile installation might merit a closer look. In general, the FCC recommends that in these higher powered installations, the antenna be located such that the vehicle occupants will be shielded from the antenna during normal use.

And while many classes of amateur stations are categorically exempt from the need to do a station evaluation, there are circumstances under which the FCC could require a station evaluation or take other action. An example of this might be a transmitting antenna located in an attic or a balcony-mounted antenna a foot or so away from a neighbor.

When routine evaluation of an amateur station indicates that exposure to RF fields could be in excess of specified limits, the licensee must take action to correct the problem and ensure compliance. Such actions could be in the form of modifying patterns of operation, relocating antennas, revising a station's technical parameters such as frequency, power or emission type or combinations of these and other remedies. Amateur stations are also expected to follow a policy of systematic avoidance of excessive RF exposure. The FCC said that it will continue to rely upon amateurs, in constructing and operating their stations, to take steps to ensure that their stations comply with the MPE limits for both occupational/controlled and general public/uncontrolled situations, as appropriate. In that regard, for a typical amateur station located at a residence, the amateur station licensee and members of his or her immediate household are considered to be in a "controlled environment" and as such are subject to the occupational / controlled MPE limits. All persons, with particular emphasis on neighbors, who are not members of an amateur station licensee's household are considered to be members of the general public, because they cannot reasonably be expected to exercise control over their exposure. In those cases, general population/uncontrolled exposure MPE limits apply. Similar considerations apply to amateur stations located at places other than a residence.

One last point should be made here. In most cases, the FCC will rely on amateurs to determine for themselves how the evaluation requirements apply to their stations, but under the rules, the FCC does have the flexibility to ask that an evaluation be performed on any transmitter regulated by the FCC. Even though your particular amateur station may be exempt from evaluation, it is perhaps a very good idea to conduct one anyway and retain the paperwork on file for viewing by any interested party. In this fashion you are demonstrating a spirit of cooperation and goodwill.

73 es best DX……de NE1V

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