Field Intensity Measurements at Frequencies from 285 to 5400 Kilocycles per Second

Radio field intensities were measured at distances of only a few wavelengths from a transmitting station on a wide range of frequencies, including the broadcast band, in order to determine the distance at which ground absorption became appreciable. At a distance of 2.4 kilometers, there was no appreciable absorption for frequencies below about 1000 kc; above this frequency, the absorption became appreciable and increased as the frequency was increased. Measurements made at greater distances on broadcast transmissions, airways phones, and airways beacons show that field intensities fall off to one per cent of what the inverse distance law with no absorption would give at distances from 100 to 400 kilometers depending on the frequency and the nature of the ground. The experimental data were compared with Rolf´s attentuation graphs in order to determine the electrical constants of the land east and west of the Allegheny Mountains. East of and including the mountains (Maryland, Pennsylvania, and New Jersey) the conductivity and dielectric constant were found to be 3.35 × 10^-14e.m.u. and 13, respectively; west of the mountains (near Chicago) they were found to be 1.07 × 10^-13e.m.u. and 13, respectively. Using these constants theoretical values of field intensity were graphed for these two types of ground and for broadcast frequencies. The experimental data were also compared with results given by the Austin-Cohen transmission formula.