Long delayed echo

Long delayed echo or LDE is an echo of radio waves that return to the sender a few seconds after transmission. A delay of more than 2.7 seconds is considered LDE.

History

Echo was first observed in 1927 by radio engineer Jorgen Hals during his work near Oslo, Norway. Hals observed an unexpected second radio echo with a considerable delay after the completion of the primary echo.

Unable to understand this phenomenon Hals in a letter to Norwegian physicist Carl Størmer asked him for help. Both scientists joined another physicist, Balthasar van der Pol. They have been studying this phenomenon for several years, but have not managed to find an explanation. The reason was that the echo delay time changed dramatically. One of the findings was that if the echo is a reflection of any region of the Earth's atmosphere or from any body in space (such as the Moon), the echo delay would be predictable. Theory

The reason is probably the ionosphere. The most popular circuitry theory is that radio signals repeatedly circulate the Earth inside the waveguide that would have to create "instantaneous" configurations of the same electron density layers at different heights above the surface. This wave can be recorded with a very long delay by the ground detector after leaving the area. This confirms that multiple images of the entire ionosphere layer can be obtained, rather than just a specific frequency.

The hypothesis of multiple radio waves from the Moon's surface is relatively unavoidable, as in this case, the delay of the signal can be determined as a multiple of the distance from the natural satellite (eg, EMEME) - the reflected signal from the Moon would be reflected from the Earth and again from the Moon, and then recorded on the surface of the Earth.)

A few groups believe that LDE signals are Bracewell's "alien" transmissions trying to communicate with us by bouncing our own signals.

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