Spectrum Analysis of VLF Emissions
Department of Electrical Engineering, Stanford University., 1968 - Electric waves - 47 pages
Amplitude analysis of discrete VLF emissions using the Rayspan spectrum analyzer showed characteristics that are not readily detected using the conventional 'frequency' spectrograms. From a small sampling of discrete VLF emissions recorded at various ground stations, the following observations were made: Rise and fall times may be as small as 15 - 20 msec; Emissions that appear 'single' on a frequency spectrogram may consist of closely-linked shorter emissions, each having a duration of the order of 100 msec; Frequency modulation, previously suspected in some frequency spectrograms, is confirmed. In the samples studied the frequency of modulation ranged from 35 Hz to 70 Hz, while the frequency deviation lay mainly in the range 25 Hz to 50 Hz. (Author).
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SPECTRUM ANALYSIS USING THE RAYSPAN INTENSITY SPECTRUM
B The Amplitude Analysis of VLF Emissions
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20 July 20 msec 33 msec AMPLITUDE ANALYSIS amplitude spectrogram Amplitudes and frequencies Antarctica Eights Station emission rising tone falling tone recorded Figures 3.3 frequencies and amplitudes Frequency modulation Frequency spectrogram frequency variation rate graphs ground waves Helliwell hook Hz sweep frequency input signals ionosphere kHz/sec l0-20 kHz range l00 msec l000 mm/sec film l4.7 kHz NAA l400 Wilson Boulevard l50 Hz sweep l50 sweep mm/sec film speed moving film NAA Morse-code Naturally Occurring VLF number of emissions number of VLF off-set oscilloscope overall frequency variation Radioscience Laboratory Rayspan characteristics Rayspan filters Rayspan Spectrum Analyzer Rayspan technique recorded at Eights rise and decay riser followed rising tone measured scanning shown in Fig Sonagraph technique Spectrum Analyzer technique Stanford University step response triggered emissions triggered rising tone U.S. Air Force VLF discrete emission VLF emission signals VLF emission triggered whistler-mode echoes whistler-mode signals Wilson Boulevard Arlington Wright-Patterson AFB