High-frequency propagationpredictions

This chapter will give the reader a brief idea of the ways in which ionospheric data are applied to high-frequency communication problems. Several computer programs, available for both mainframe and personal computers, make it possible to determine optimum frequencies, signal strengths, broadcast coverages, and so forth. For the determination of required transmitter power, for a specified grade of service, maps of worldwide distribution of radio noise and its variability are available in CCIR (1988). Ionospheric predictions are useful in planning systems, selecting frequencies, and assessing interference (intentional and otherwise) between systems. They are valuable in the overall frequency management of the high-frequency band. Ionospheric data are of value to (i) short-term operators who have to react to circuit interruption because of MUF failure, high absorption, excessive fading, and (ii) long-term system planners and frequency managers who are involved with the installation of terminal equipment, antenna design, compatibility and cost. This chapter is concerned, primarily, with the second category. We also consider real-time channel assessment in which probing signals (e.g. oblique soundings) are used to evaluate the channel capacity. Such evaluations are of particular use to traffic controllers and circuit operators. We consider predictable characteristics, their temporal and spatial variabilities, some specific prediction systems, and applications to communications.