Extreme useful range of VHF transmission by scattering from the lower ionosphere

Results are given from an experimental study of VKF propagation in the extreme distance range for scattering from the lower ionosphere. Signal intensity at 36.0 Mc/s was measured continuously for a year over the 1411 mile path from St. Johns, Newfoundland, to Terceira Island, The Azores, using high transmitting and receiving sites. The median transmission loss is approximately 13 decibels greater than for the same system operated over the 773 mile path Cedar Rapids, Iowa, to Sterling, Virginia; this ratio is interpreted in terms of the geometrical restriction of the effective scattering volume. Less pronounced diurnal and seasonal variation is related to occluding by earth curvature of scattering from heights below about 80 Km. Continuous "height gain" observations give evidence of variation of scattering height diurnally and seasonally. Results are given on the nature of the signal fading, space-correlation, realizable gain from arrays having extensive vertical aperture, and polarization effects.