Short-haul communications using NVIS HF radio

In geographical regions poorly served by land-lines or line-of-sight repeat ers, high-frequency (HF) radio can still provide a low-cost alternative to satellite links. In particular, the near vertical incidence sky-wave (NVIS) propagation mode gives omnidirectional coverage from a central site; 300 k m ranges are possible and the technique has an inherent ability to fill in 'blind spots' lying in hilly ground. Normal voice and data services may be readily established. This paper introduces NVIS radio, discusses some of it s roles to date and examines the hardware required for basic link implement ation; emphasis is placed on antenna design and selection. Channel availabi lity and fading characteristics (depth and frequency) gathered from a 6793 kHz oblique sounder over the 1997/8 winter-summer transition are included t o illustrate the potential of the technique for non-real-time remote monito ring applications.