Frequency Adaptive Communication Systems and Networks in the MF/HF Bands


image of Frequency Adaptive Communication Systems and Networks in the MF/HF Bands

This Handbook is published to assist planners and decision-makers in the deployment of adaptive MF/HF systems in the fixed service, for both commercial and government users in developed and particularly developing countries. It provides material on current present technological capabilities in the field of adaptive MF/HF communications.




Terrestrial communication at HF to long ranges has been in use for nearly 80 years. The mode offers relatively low-cost installation and flexibility, as well as the capability of communication ranges far beyond the horizon without the costs and complexity of intermediate relay stations. However, the ionosphere is highly variable in all time scales: within an hour, through the day, from season to season and with the 11-year solar cycle. Moreover, ionospheric storms, due to solar disturbances, can cause significant rapid change to the range of frequencies available. Thus, traditionally, HF radio stations have been controlled by skilled operators who would change the operating frequencies from time to time, at least several times each day, in response to changes in signal strength and quality. However, they may not have had available appropriate frequency assignments to ensure optimum communication in all circumstances, and the crowded state of the spectrum often resulted in interference.


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