For the past 3 years, we have participated in various extremely low frequency (ELF) propagation tests. During these tests, receiving sites were located in Connecticut, North Carolina, Maine, Utah, Nova Scotia, California, Greenland, the Virgin Islands, Alaska, Norway, Hawaii, Greece, and Saipan. Measurements have also been taken sporadically in Connecticut since June 1970. At each location, the horizontal magnetic field strengths were measured at a band of frequencies centered at 45 Hz and 75 Hz in order to determine the average attenuation rates and relative excitation factors for daytime and nighttime propagation conditions. The U.S. Navy ELF Wisconsin Test Facility was the transmission source. The principal results obtained from these measurements were 1) the daytime attenuation rate is usually higher than the nighttime attenuation rate at both 45 and 75 Hz; 2) the relative excitation factors are quite different for daytime and nighttime propagation conditions; 3) nighttime propagation is more variable than daytime propagation; 4) there is a seasonal variation in the ELF propagation parameters; and 5) auroral-zone effects appear to be present at both frequencies.

During August and September 1971, the New London Laboratory, Naval Underwater Systems Center, performed pattern and steering measurements on the Wisconsin Test Facility (WTF) antennas. The pattern measurements were made at 13 locations in Minnesota and Wisconsin (covering approximately 120° of arc), while the far-field steering tests were taken in Maine and North Carolina. To be certain that the receiving sites were acceptable, several components of the received magnetic field were measured at each site and plotted on a normalized cosine curve. The 45- and 75-Hz pattern measurements were made at a range of approximately 300 km, while the steering measurements were performed at 1.7 Mm. The principal results from the pattern and steering measurements were 1) the east-west (EW) antenna pattern is skewed clockwise; 2) the north-south (NS) antenna pattern is skewed counterclockwise; and 3) the effective conductivity under the EW antenna is greater than the effective conductivity under the NS antenna.

In March and April 1973, the 76-Hz magnetic field strength, produced by the Wisconsin Test Facility elevated and (newly installed) buried north-south antennas, was measured in Wisconsin and Texas. The principal result obtained is that there is no measurable difference in performance between the two antennas.

A limited amount of extremely low frequency (ELF) horizontal magnetic field strength measurements have been taken in Connecticut during the past 3 years. The transmission source for these 1.6 Mm range measurements was the U. S. Navy ELF Wisconsin Test Facility. The principal result obtained from these measurements is that there are considerable variations in the ELF nighttime propagation parameters.