most commonly used by amateurs are Yagi and dipole antennas. Several other antenna types were also encountered, including vertical radiators, whip antennas, a VHF discone, and a "Quagi" antenna. The highest operating power level observed during the study was 1400 watts, at Station "F." Attempts were made at other stations to use power levels that were as high as practical in order to create "worst case" situations.
Examples of maximum electric and magnetic field strength levels measured at the amateur sites are given in Tables 2-4.
Commonly encountered field strength readings in accessible areas near antennas and equipment generally were in the range of 1-20 V/m for the electric field and less than 50 mA/m for the magnetic field. Maximum readings obtained in accessible areas within a few meters of some antennas and equipment were as high as 237 V/m and 1350 mA/m, but readings this high were not common. In general, the highest readings in accessible areas were associated with vehicle-mounted antennas, which are generally located at or near ground-level, and wire antennas, such as dipoles, that may be mounted just above a roof or yard.
The values obtained in this study represent what we believe to be reasonable examples of "worst-case" exposure levels for the antenna sites surveyed. In particular, since transmissions were "key down," i.e., continuous-wave unmodulated signals, they would not be common during routine communications. Normally there would be a duty factor associated with an amateur transmission that should be significantly less than 100%. Safety guidelines incorporate time-averaging provisions for evaluating human exposure that would take into account duty factors.2
Tables 2-4 also show a comparison of measured maximum field-strength values with RF exposure guidelines issued by the American National Standards Institute (ANSI) in 1982 (ANSI C95.1-1982, see Reference 1) and also with recent guidelines issued by the Institute of Electrical and Electronics Engineers (IEEE C95.1-1991, see Reference 2) that replace the previous ANSI C95.1-1982 guidelines (ANSI adopted the IEEE guidelines in 1992 and designated them ANSI/IEEE C95.1-1992). The FCC currently applies the 1982 ANSI guidelines for purposes of evaluating RF exposure. However, in 1993 the Commission proposed to begin using the new ANSI/IEEE guidelines in the future.3 Both exposure guidelines are frequency dependent and recommend safe levels that are based on averaging exposure over a given period of
See ANSI and IEEE guidelines (Appendix B).
3 Federal Communications Commission,Notice of Proposed Rule Making, ET Docket 93-62, 8 FCC Record 2849 (1993) 58 Federal Register 19393 (1993). Also, 8 FCC Record 5528 (1993), 9 FCC Record 317,985, 989 (1994 , 58 Federal Register 43091, 60827 (1993) and 59 Federal Register 3050, 9171 (1994) [extension of comment deadlines].