Recent work on the measurement and analysis of spectral occupancy at HF

Since 1982, a long term programme has been undertaken at UMIST to measure and analyse spectral occupancy across the entire HF band 1.6-30 MHz. The aim of the work is to provide experimental data and mathematical models, showing how occupancy varies with frequency, time, bandwidth, threshold level, type of user allocation, antenna, and geographical location. From 1982 to 1989, the measurement site was RSRE, Pershore, Worcestershire, a rural site in central England which was available at the times of the solstices. In 1989, a dedicated measurement system was installed at the Radiocommunications Agency monitoring site, at Baldock, Hertfordshire. A data link between UMIST and Baldock enables system control and transfer of results. In 1990, an identical measurement system was set up by the Swedish National Defence Research Establishment at LinkSping, Sweden, and an agreement made for the simultaneous operation of the two sites, and for data exchange. In 1993 a third system was installed by UMIST and DRA at the antenna site of Rohde and Schwarz near Munich, Germany, again linked to UMIST for control and data transfer. These three sites are approximately at the corners of an equilateral triangle of side length 11000 km, and provide effective measurement of spectral occupancy over northern Europe. The introduction of automatic systems has meant that occupancy measurements are not restricted to the solstices, and this paper is based on results taken at more frequent time intervals