Interference data were collected in the HF band (2–30 MHz) during a Pacific transit. Measurements were made during four time periods corresponding to midday, midnight, and the sunrise and sunset transition periods. Man-made signals (other users) were the predominant interference source between the maximum observed frequency (MOF) and the lowest observed frequency (LOF). The occupancy statistics and power levels were found to exhibit characteristic curves for each time period, with the maximum percentage occupancy and power level falling between the expected MOF and LOF. Typical other user occupancy between the MOF and LOF was about 50%; however, occupancies as high as 80% were observed near Japan at certain times.
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