An assessment of the propagation characteristics of the HF NVIS channel

Higher data rates are required over HF (high frequency) radio links in order to meet the ever increasing demands for information transfer. This requirement extends to HF near vertical incidence skywave (NVIS) links which are used when terrain obstructions preclude the use of other radio transmission methods. This paper provides a significant update on a previous paper that set out to investigate the channel characteristics of HF NVIS links and the implications for high data rate transfer. The previous study was based on data collected over a four month period between October 1998 and January 1999. Results in this paper extend the analysis to a total period of 14 months by adding data collected up to November 1999. In addition, it has been possible to utilise results from a measurement campaign involving experimental 16 kbps modems Hoult et al. (see 8th. IEE Conference on HF Radio Systems and Techniques) and more detailed channel measurements to predict link availabilities