Local inhomogeneities in the ionosphere cause coupling from the transmitted transverse wave to the plasma wave, and from the plasma wave to a transverse wave which can propagate back to the earth. (Skip to 2:29 for a clip of the finished film)This blog ties up some loose ends to do with my graduation film, Long Delayed Echo, which was the subject of m. Delay is an audio signal processing technique that records an input signal to a storage medium and then plays it back after a period of time. A weak beam-plasma instability, due to the presence of electrons precipitating into the ionosphere, is postulated as a means of offsetting collisional and collisionless attenuation of the plasma wave. Controlled experiments where delays ranged from 3 to 30 seconds confirmed the phenomenon and convinced. His first report exists at the National Library in Oslo and was later reported in Nature Størmer, 1928. A mechanism for producing LDE was studied which involves signal propagation in an electron plasma wave mode at very low group velocity. The first radio echoes with long delays were reported in 1927 by Jørgen Hals in Oslo, Norway on 9.54 MHz signals from the Netherlands.
Although none of the possible LDE received reproduces exactly the transmitted signal, many exhibit features that seem unlikely to have been generated except by an LDE mechanism. The tapes were later audited for possible long delayed echoes LDE. The experiment involved transmitting a radio signal, and tape-recording the output of a receiver gang-tuned with the transmitter for the following 30 s interval. Abstract: The thesis describes an experimental program carried out over a five-year period.
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