Ionospheric ducting is a term used to describe how fragments of radio broadcasts or walkie-talkie communications can travel thousands of miles by occurring in electronic layers of the ionosphere that create small “ducts” that allow them to travel great distances. The observational evidence for long-range propagation of high-frequency radio signals began to accumulate in 1926 when transatlantic communication links had been established. In 1927, signals were detected that had propagated over large distances or circled the Earth with little attenuation.*
According to Jurgen Graff, a former engineer at Telefunken, “a taxi driver communication in New York could suddenly be monitored for a couple of minutes in Europe. After a few minutes the ducts collapse and the phenomenon disappears.” (Roach, p. 188).
It is likely that some of the recordings put forth as evidence of spirits communicating from the afterlife are due to ionospheric ducting.