  A multipath mechanism similar to that used in Australia sixty years ago by
the Sea-cliff Interferometer is shown to generate correlations between the
periods of oscillations observed by two distant radio telescopes pointed to the
Sun. The oscillations are the result of interferences between the direct wave
detected in the main antenna lobe and its reflection on ground detected in a
side lobe. A model is made of such oscillations in the case of two
observatories located at equal longitudes and opposite tropical latitudes,
respectively in Ha Noi (Viet Nam) and Learmonth (Australia), where similar
radio telescopes are operated at 1.4 GHz. Simple specular reflection from
ground is found to give a good description of the observed oscillations and to
explain correlations that had been previously observed and for which no
satisfactory interpretation, instrumental or other, had been found.
