Energy Spectra for Frequency-Shift-Keyed Signals Transmitted by Synchronously Resonated,Very Low Frequency Antennas.

摘要

Electronic broadbanding is a technique whereby very low frequency (VLF) antennas can be resonated (retuned) synchronously with a frequency-shift-keyed (FSK) signal for transmission of binary data at rates well over 1000baud. The thesis investigates the transmitted energy density spectrum for an electronically broadbanded VLF antenna system in which a frequency shift can occur only at the instant of an antenna-current zero-crossing with positive slope. A computer solution shows that the transmitted spectrum is approximately equivalent to the spectrum of an ideal,constant amplitude,FSK signal. A further investigation,again by computer program,shows that if the total frequency shift between the marking and spacing frequencies occurs over a finite period,rather than instantaneously,then the spectrum's sidelobes will be reduced significantly. (Modified author abstract)