What is Transequatorial Radio Propagation?

 Transequatorial VHF propagation was first noted by radio amateurs in August 1947 when Mexican stations could work Argentine stations regularly across the equator in the late afternoon and early evening on 50 MHz. This occurred for few more years during the maximum of Solar Cycle 18. Transequatorial Propagation came down during the period of sunspot minimum and reappeared in 1955 and continued through the maximum years of Solar Cycle 19. We can expect similar conditions as we are heading for the maximum of Solar Cycle 25 in 2025.

Two types of transequatorial propagation has been described. One occurring during late afternoon and early evening with maximum distance of about 6000 km in low VHF band of 6 m. Second one was between 7 pm to 11 pm local time with contacts on 2 m and sometimes on 70 cm band. Mechanism by which transequatorial propagation occurs is the presence of equatorial anomaly, which is a high concentration of electrons on either side of the equator in the region of 10 to 20 degrees latitude.  The signals are reflected by one anomaly to the other and then back to the ground on the opposite side of the equator. So contacts are possible between stations equidistant from the equator.