Studies of RF Biological Hazards from High Power HF Transmitters

A one-year research program is reported concerning an intensive investigation into biological RF radiation hazards from high power, high frequency (HF) antennas. This program consisted of two major phases: the measurement of field strengths in the near vicinity of high power HF band antennas, and coordinated clinical irradiation studies using male albino Wistar rats as the test specimens. An extensive survey was made of the literature concerning other investigations of biological hazards from radio-frequency irradiation of men and laboratory animals. Past studies have been focussed on radiation hazards at radar frequencies, typically extending from 200 MHz to 10,000 MHz. The annual Tri-Service Conferences on Biological Effects of Microwave Radiation, culminating in the fourth conference in 1960, have brought forth valuable and definitive reports on research in UHF radar bands, which have provided useful guidelines and background information for the current investigation. Recent studies have also been reported concerning magnetic field effects at DC and low frequencies. Little relevant research on biological hazards in the HF band has been reported in the literature, although the USA Standards Institute has recently published a standard extending the microwave power density limit of 10 mw/cm2 to cover the frequency range from 100 GHz down to 10 MHz. This standard covers a portion of the HF band, but not all, and there is no evidence that it can properly be applied to the near zones of the antennas and transmission lines where the field measurements showed the highest intensities.