High frequency spectral occupancy at the solstices

Since 1982, the Digital Communications Group at UMIST has systematically measured and analysed the occupancy of the HF spectrum. The authors describe the measurement system and measurement procedure, and give mathematical models for solstice day and night occupancy across the whole HF spectrum. The main problems of the HF channel may be broadly stated as: (a) problems arising from time-varying multipath propagation; (b) interference from other HF users; and (c) atmospheric and galactic noise. Propagation and noise have been extensively studied and documented. However, interference from other HF users, although frequently very severe, has been seen as less obvious to characterise