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An Investigation of the Modal Interference of VLF Radio Waves
Author(s) -
Rhoads F. J.,
Garner W. E.
Publication year - 1967
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1002/rds196726539
Subject(s) - interference (communication) , isotropy , modal , acoustics , range (aeronautics) , physics , mode (computer interface) , field strength , fading , geology , computational physics , telecommunications , optics , materials science , magnetic field , engineering , computer science , channel (broadcasting) , quantum mechanics , polymer chemistry , composite material , operating system , decoding methods
An experiment was carried out to study modal interference effects and the extent of agreement with theoretical results obtained previously. Field strength data for transmission from two stations in Hawaii on several frequencies between 16.6 and 26.1 kHz and from NPG on 18.6 kHz were recorded aboard an aircraft while in flight between California, Guam, Japan, and at a ground site near Washington, D.C. The experimental observations show considerable modal interference and very good agreement with the theoretical results for the isotropic case. For frequencies above 20kHz 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 Mm. The data at 19.8 kHz, however, indicate 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 kHz, which was expected from theory.