Abstract
A NOVEL explanation of some peculiar whistles audible under certain conditions in short-wave radio receivers is put forward by S. R. Khastgir (Indian J. Phys., 17, 239; 1943). Weak short-lived whistles of rapidly descending pitch have been noticed at the Delhi receiving station of All-India Radio when a receiver is tuned to the carrier wave of the nearby short-wave transmitters. Two possible explanations are offered, in both of which the phenomenon is attributed to the entrance of a meteor into the earth's upper atmosphere. In the first, the meteor is supposed to produce a rapidly moving mass of ionized air at its head. This local Heaviside layer scatters the incident radiation from the transmitter, the rapid descent causing a Doppler change in the frequency of the scattered waves. These then interfere with the ground waves reaching the receiver, and an audible beat note is produced. As the descent is retarded by atmospheric resistance the Doppler shift lessens, and the pitch of the whistle drops. On a carrier wave of 7 Mc./s. a whistle starting at 3,000 c./s. would be caused by a meteor with a maximum velocity component of 64 km./s. towards the receiver—not an unreasonable value.
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Relation of Meteors to Short-Wave Radio 'Whistles'. Nature 155, 602 (1945). https://doi.org/10.1038/155602a0
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DOI: https://doi.org/10.1038/155602a0