Investigations of Scattering and Multipath Properties of Ionospheric Propagation at Radio Frequencies Exceeding the MUF

Some results are given of studies of ionospheric forward scatter propagation at frequencies exceeding normal muf in the high hf and low vhf range with the view of investigating potential point-to-point communications. Approximately 13,000 hours of data were analyzed from measurements conducted since late 1951, on several frequencies and paths, predominantly 1,000 to 1,100 miles in length, in mid-latitudes. Signal level characteristics are presented in summary form and discussed. Most of the work was conducted at 49.6 mc on the 1,066 mile Cedar Rapids, Ia. to Round Hill, Mass. path. Nominal 30 kw transmitters and large rhombic transmitting antennas were employed. The median received signal levels were relatively weak, of the order of 100 db below free space values. Fading during short periods in the absence of meteoric or sporadic E enhancements was found to be Rayleigh distributed. For longer periods, of the order of an hour, the fading was essentially Gaussian, although meteoric and sporadic E enhancements often changed the slope of the fading distribution curves at higher signal levels. The normalized median levels were generally lower and the diurnal variations less marked than those reported by CRPL for the shorter Cedar Rapids to Sterling path (773 miles). Seasonally, the median levels were higher in winter and summer and lower in spring and fall. There was an indication of lower levels with decreasing sunspot activity.