Some Tropospheric Scatter Propagation Measurements near the Radio Horizon

Measurements of small variations in 100 mc field intensity within and just beyond the radio horizon are reported. The measured fields are assumed to be the resultant of two field components, one having a constant amplitude and the other being a rapidly-fading scattered component. The fading range of the resultant field intensity over a 10-minute period is used to determine K. Here, K is the ratio in decibels of the root-mean-square amplitude of the scattered component to the amplitude of the constant vector. Curves showing the measured median values of basic transmission loss, fading rate, and K plotted vs hour of the day are included for three of the Cheyenne Mountain transmission paths. Diurnal variation of these quantities is also discussed. The average basic transmission loss of the scattered component, Lba8, can be found if K and the resultant basic transmission loss, Lbm are known. Median values of Lba8 and Lbm are plotted vs the angular path distance, ¿. Measurement of the correlation of the resultant field strengths received on two horizontally-spaced antennas within the radio horizon is reported. When the spacing was varied from ¿ to 20 wavelengths and the correlation compared to other characteristics of the field, the correlation was found to be as much a function of Lba8 and fading rate as it was of antenna spacing.