Vice reports that radio operators have received echoes occurring approximately 3 seconds after a broadcast since at least 1927. Broadcasts take about 1/7 of a second to travel around the Earth, so a 3 second delay doesn’t make sense: “Long-Delayed Echoes (LDEs) set off a frenzied investigation into this unsettling phenomenon in the following years, although just what accounts for these echoes still remains a mystery.”
Radio Ghosts Have Haunted the Airwaves for Nearly a Century.