For many decades of the 20th century the HF electromagnetic spectrum of 3-30 MHz was the principal waveband for long distance radio communications and represented an important tool for applied science and for radio users, now still widely used around the world for important purposes including radio frequencies dedicated to emergency services, strategic implementations, and radio services.
Considering that the reflecting layers of the ionosphere are subject to solar-terrestrial interactions and disturbed conditions, the variability of its condition plays an important role for the performance of radio communications and for the choosing of the best radio frequency to use.
The basic principles of ionospheric radio propagation for HF communication and the ionospheric long term prediction methods as well as the ionospheric now casting and forecasting methods widely available on line are here shortly described.
The monthly prediction of the hourly HF set of frequencies over the N radio links given by the network, based on the available ionospheric models and methods and the daily forecasting and now casting of the hourly HF set of frequencies based on the Mediterranean ionospheric measurements for the frequency plan for the example month April 2013 are here presented.
Finally concluding remarks and considerations the frequency management are reported in the conclusions.