time. A summary of major features of the ANSI/IEEE guidelines are given in Appendix B of this report.4
Although current FCC policy categorically excludes amateur operators from routine evaluation for compliance with RF guidelines, this policy is one of several items being reconsidered in the recent proposal to adopt new guidelines. In the tables, ANSI/IEEE limits specified for "uncontrolled environments" are used for comparison with measurements in publicly accessible areas, and limits specified for "controlled environments" are used for comparison with measured values obtained at the amateur station or "ham shack."
Table 2 lists examples of maximum electric field strengths measured in publicly accessible areas near the various antenna sites. The data are arranged in terms of increasing transmitter frequency. "Publicly" accessible areas are defined here as areas, other than the "ham shack," where it is reasonable to assume that persons who might not have control or knowledge of their exposure could have access. This is roughly equivalent to the definition of an "uncontrolled" environment given in the ANSI/IEEE guidelines. Stricter exposure limits are specified for such situations than for "controlled" environments. According to the guidelines, an amateur operator would be in a "controlled" environment and subject to less restrictive limits (see Appendix B).
The exposure guidelines are frequency-dependent and recommend the strictest exposure limits for VHF frequencies, since these are the frequencies where the highest specific absorption rates (SARs) occur for human beings.5 Therefore, although some measured field strengths at HF frequencies may be relatively high, the percentage of the exposure limits may be less than for lower field strengths measured at VHF frequencies.
According to the new ANSI/IEEE exposure guidelines, it appears that vehicle- mounted amateur antennas can create the greatest possibility for significant exposure in publicly accessible areas. In fact, in several cases involving vehicle-mounted antennas, the maximum levels measured approached or exceeded the electric field strength limits recommended for "uncontrolled" environments. This also occurred in at least one other case, a center-fed dipole at Station E. However, it is important to
4 The ANSI/IEEE guidelines are the most commonly utilized exposure guides. However, exposure criteria have also been published by the National Council on Radiation Protection and Measurements (NCRP, Reference 3) and the International Radiation Protection Association (IRPA, Reference 4). In general, the NCRP and IRPA guidelines are similar to the ANSI/IEEE C95.1-1992 recommendations with regard to power density and field strength values, particularly with regard to commonly-used amateur frequencies.
5 Specific Absorption Rate (SAR) is a measure of the rate of energy absorption per unit mass, usually expressed in watts per kilogram (W/kg). Exposure guidelines are based on SAR. For example, the ANSI/IEEE guidelines allow a whole-body SAR of 0.4 W/kg.