Radio Field Intensity and Distance Characteristics of a High Vertical Broadcast Antenna

During December, 1934, field intensity records of emissions from radio station WBT, Charlotte, North Carolina, were made at seven different distances from the transmitting station before and after the construction and use of a high mast antenna. In addition, field intensity measurements were made at eight points on a circle at a distance of one mile from the transmitting station. The results showed that the substitution of the mast antenna for the older T and L antennas produced much greater ground-wave field intensities near the transmitter and somewhat greater total field intensities at greater distances. At the same time the amplitude of the fading was reduced at the first three recording stations at distances sixty-nine to 142 kilometers. The fading at these first three stations was of a more rapid type than at the more distant stations. The antenna change did not appreciably affect the frequency of the fading. Wires were added to the mast antenna to increase its top capacity and thus make the current distribution in this antenna more nearly sinusoidal. This change seemed to reduce the fading amplitude at the first three recording stations by the suppression of certain high angle radiation rather than by an increase of the intensity of the ground wave. With all conditions of the transmitting antennas used greater values of the averages of the ten-minute peak field intensities were recorded at the receiving station at Meadows, Maryland, 552 kilometers, than at any other station from sixty-nine to 879 kilometers.