Propagation Measurements in the Extremely Low Frequency (ELF) Band

An experimental measurement program has been conducted to determine propagation parameters in the 40-50 and 70-80 Hz ranges. These measurements have utilized a transmitter in Wisconsin radiating a sinusoidal signal at radiated power levels of 0.5 W at 45 Hz and 1 W at 75 Hz. Sites have been located at Nova Scotia, California, Utah, Hawaii, Norway, Greenland, Greece, and Saipan. Using sites on the same great circle path as the transmitter, it has been possible to estimate average attenuation rates and excitation factors with high accuracy subject to the constraints discussed in the paper. Both daytime and nighttime attenuation rates and excitation factors are discussed.