The high reliability of very low frequency (VLF) (3-30 kHz) propagation brings it in favour over high frequency (HF) (3-30 MHz) and low frequency (LF) (30-300 kHz) when satellite intermediates are precluded. Until recently, amateur communication has been constrained to the upper end of the medium frequency (MF) band and higher. Exploration of LF has been ongoing since the 1990s. VLF systems have been developed by innovative experimenters and global amateur VLF communication is now a reality. The success of this venture is due in large part to the understanding and application of antenna and information theory. These will be explored and an ongoing enigma will be posed in which the signal carrier vanishes during phase shift keying. The resultant spectra bear a striking resemblance to those of Doppler shifted backscatter radiation from ocean waves.
