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AN EXPERIMENTAL INVESTIGATION OF EM WAVE PROPAGATION AT 400 CPS
SPACE-GENERAL CORP EL MONTE CALIF
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An investigation of extremely low frequency ELF electromagnetic wave propagation was undertaken utilizing a stable source of 400 c power. This method has the ability to define the propagation law, determine attenuation rates, study path variations, and provide knowledge regarding coupling to the medium. During Sept. and Oct. 1961, field strength measurements were made up to 760 mi. from the transmitter. The dependence of magnetic field intensity on range is substantially in accord with the mode theory in which only the zero order mode is considered. The nighttime data points agree best with the sharply bounded ionosphere model with an attenuation rate of 2.3 db1000 km. The daytime data indicates the attenuation rate is 6.0 db1000 km. This higher absorption is explained by assuming an exponential ionosphere model. The amplitude probability distributions of 400 c atmospheric noise are similar to those in the VLF band. The median rms value of the vertical electric noise field during the test period was 100 microvoltmeter in a 40-c band. A description of the equipment and a discussion of the horizontal grounded radiator, are included. Author
APPROVED FOR PUBLIC RELEASE