AN INVESTIGATION OF THE MODAL INTERFERENCE OF VERY-LOW-FREQUENCY RADIO WAVES
Abstract
A very-low-frequency (vlf) radio-wave propagation experiment has been designed to study modal interference effects and the extent of agreement with theoretical results obtained previously. The experimental data are the field strengths of the vlf transmissions from the U. S. Navy transmitting stations NPM and Haiku in Hawaii and NPG near Seattle, Washington. These data were recorded aboard an aircraft while in flight between California, Guam, and Japan, and also at a field site near Washington, D. C. During the experiment, NPM transmitted for various periods on 16.6, 19.8, 22.3, 24.0, and 26.1 kc/s. The Haiku transmissions were on 16.6 and 19.8 kc/s, while NPG was on 18.6 kc/s continuously. The experimental field-strength-versus-distance graphs show considerable modal interference and very good agreement with the theoretical results for the isotropic case. For frequencies above 20 kc/s the experimental data indicate the existence of at least the first three modes for propagation to the west and to the east, out to distances greater than 3 megameters. The data at 19.8 kc/s, however, indicate first-three-mode effects for propagation to the east but only two modes to the west. The fading of the field strengths at Washington, D. C., during sunrise was frequently greater than 20 db. The depth of the fades, in general, increased with frequency, whereas their time of occurrence was relatively independent of frequency over the range of 19.8 to 26.1 kc/s.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 27, 1965
- Accession Number
- AD0623291
Entities
People
- F. J. Rhoads
- W. E. Garner
Organizations
- United States Naval Research Laboratory