Long Delayed Echoes

Wiki: http://en.wikipedia.org/wiki/Long_delayed_echo

Article: R. J. VidmarF. W. Crawford "Long-delayed radio echoes: Mechanisms and observations" (1985)

Article: DB Muldrew "Generation of long‐delay echoes" (1978)

Article: A.K. Goodacre "Some observations of long-delay wireless echoes on the 28-MHZ amateur band" (1978)

Article: Lawton, A. T.; Newton, S. J. "Long delayed echoes - The Trojan ionosphere" (1974)

Article:  Villard, Jr , O G ; Fraser-Smith, A C ; Cassam, R P "LDEs, Hoaxes, and the Cosmic Repeater Hypothesis" (1971)
@@@ This is the very surprising(!) Conclusion of the Authors: "In the authors' view, the extra-terrestrial-origin hypothesis in explanation of the very long delays is at the moment as plausible as any other."

Article: FW. Crawford D. M. Sears R. L. Bruce "Possible observations and mechanism of very long delayed radio echoes" (1970)