Very long distance propagation

The Combined Effects of Refraction and Coherent Scattering by Columnar Ionization Density Irregularities in Ionospheric Radio Propagation

“…Isted [1958] found RTW echoes at 37 MHz although the MUF for ground-hop propagation was not supposed to exceed 20 MHz, and radio propagation at frequencies greater than the MUF along an antipodal path was observed by Gerson [1963] and Banks [1965].…”

Design of a Satellite‐to‐Satellite Communications Experiment To Explore HF/VHF Guided Propagation in the Lower Ionosphere

“…A review of the partial experimental evidence on the existence of whispering-gallery propagation in the lower ionosphere is made by Gerson (1961]. Hess [1948Hess [ ], lsted (1960, Stein (1958], Yeh and Villard [1960], Fenwick and Villard [1962], and Gerson [1963] have reported propagation results in ground-toground tests where RTW (round-the-world) signals did propagate in regions of the ionosphere (through the dark hemisphere) at frequencies well above the MUF that one would have expected for multihop paths. "Sliding-wave" [Von Schmidt, 1936] and "chordal-hop" (ionosphere-to-ionosphere) paths have been suggested as possible mechanisms to explain the low-loss, low-dispersion propagation results obtained in these tests.…”