High-Frequency Near Vertical Incidence Skywave Propagation: Findings associated with the 5 MHz Experiment

This article collates the findings from the 5 MHz Experiment, a U.K.-based amateur radio project involving a network of beacon transmitters and monitoring stations operating at 5.290 MHz. An analysis of the calibrated received signal-power measurements, together with ionosonde frequency measurements and high-frequency (HF) signal and frequency predictions, led to a number of important results relevant to near vertical incidence skywave (NVIS) communications. The emphasis of this article is on practical aspects of this technique for both professional and amateur users of the HF spectrum.