A single-hop F/sub 2/ propagation model for frequencies above 30 MHz and path distances greater than 4000 km

Standard textbook explanations of ionosphere propagation suggest that 30 MHz and 4000 km are the limiting frequency and distance for single-hop communications. During the peak of sunspot cycle 22, however, there have been hundreds of reports of F/sub 2/ communications exceeding great-circle distance of 4200 km at 50 MHz. It is shown that parabolic F/sub 2/ ionospheric models explain this propagation irregularity, although textbooks and reference books fail to show that such long distances at VHF are possible.<>