Daily Facts
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Aurora Sputter Fading

July 24th Fact-of-the-Day

A particular type of very-rapid and easily-recognizable VHF signal fading was first heard in the 1930's where there were relatively-long radio-signal propagation paths in Artic aurora regions. The fading effect became known as 'sputter,' because signals faded at rapidly-changing aperiodic rates of several hundred Hertz which made them sound as if they were being amplitude modulated by a sputtering noise. It was discovered later that sputter sometimes affects HF as well as VHF signals. A puzzling aspect of sputter is that even though it is clearly associated with aurora, it doesn't always occur with aurora and when it does occur it doesn't seem to be associated with any specific types of aurora. The University of Manchester in Canada and Cornel University in the United States both studied the phenomena long ago and concluded that the sputtering sounds probably are due to Doppler shifts when signals reflect from the ionized trails of very-high-velocity particles moving through the ionosphere. ©2005 Martek International All rights reserved.


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