Spatial correlation measurements on one-hop HF radio waves

The spatial correlation of amplitude of one-hop HF radio waves, propagated via the ionosphere with a 2077 km ground range, has been measured using three receivers positioned at the corners of a triangle. The spatial correlation was found to be approximately isotropic for spacings up to 1 km. The antenna spacing at the 0.5 level of amplitude correlation was greater than 3 km if the shape of the spatial correlation contours were assumed to be independent of spacing.